cell

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transgenic cells/transgenic organisms

The future of genetic research

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found by ordinary means. Dystrophin plays a key role in muscle cells and

2 Sugars

Amylose and cellulose, composed of long chains of glucose molecules, are examples of polysaccharides. The only structural difference between them is the linkage between the glucose molecules, yet the compounds have very different properties. Cellulose is a tough material found in plant cell walls, whereas amylose (a form of starch) is water soluble and used by plants as a carbon storage compound.

Control of the Cell Cycle

Control of the Cell Cycle

Control of the Cell Cycle

The process of cell division in mammalian cells can readily be

observed in the light microscope. In some types of bacteria, cell

division involves a simple elongation of the bacterial cell and the

pinching off of two equally sized daughter cells. But the process of

cell division as seen in mammalian cells is much more complicated. This

two ends of the dividing cell; the constriction through the equator of

the cell that results in the pinching off of two daughter cells, each

membrane in the daughter cells. A detailed discussion of the multiple

This process of cell division in mammalian cells is one of

each of the daughter cells receives the proper, equal allotment of

chromosomes and is able, following cell division, to re-form into a

perfect, independently functioning cell, separate and distinct from its

sister. But there are other parts of the cell's life cycle that are

growth and division that characterizes the life of a mammalian cell.

Eukaryotic cell cycle

While we discuss the mammalian cell life cycle here almost

with almost all other types of eukaryotic cells. The steps of cellular

growth and division that we observe today in our own cells were already

developed in the original eukaryotic cells more than 1.5 billion years

types of eukaryotic cells as they proceed through their cycles of growth

and division. For example, the life cycle of the yeast cell is almost

identical to that of a human cell.

The entire life cycle of a cell is termed simply the cell cycle.

Following cell division (i.e. mitosis), the daughter cells confront two

This leads to repeated rounds of cell division and results in turn in an

exponentially increasing cell population.

As an alternative, the daughter cells may decide to cease active

growth for a while. In that case, they will exit the active cell cycle

phase of the cell life cycle. Most of the cells in our body are in GO,

retreated into a non-growing state. Should conditions require, a cell

may leave GO and reenter the active cell cycle.

In fact, only a small percentage of cells in our body are in an

the bone marrow, skin, and the gut, continual cell division occurs to

replenish the constantly dying cells in those organs. In other tissues,

such as the brain, cell division is a rare event.

cells emerging from mitosis to remain in the active growth cycle. Each

of these cells, recently formed through cell division, must now begin

immediately to prepare itself for the next round of cell division. The

time between mitoses in most mammalian cells is on the order of 12 to 24

contrast may divide every 20-30 minutes, and yeast cell and other

cells, all of which are actively growing, will double in number every

12-24 hours. During early embryogenesis, most of the cells in an embryo

will be involved in active growth, and the number of cells will increase

embryogenesis, an ever-decreasing proportion of cells are involved in

active growth. In adults, only a small proportion of cells are in the

active growth cycle, proliferating in order to replace cells that have

died as a consequence of normal cell turnover or tissue damage. Some of

the remaining cells are in G0. Yet others are in a quiescent state that

precludes them from ever re-entering the active growth cycle. Such cells

build-up of new molecules by a cell and the associated increase in its

obvious that in most exponentially growing populations of cells, cells

ensure that the mass of the 2 daughter cells (including all their

constituent parts) will equal that of the mother cell prior to division.

Replication of the Cell's Genome

preparation for cell division is the cell's chromatin--it's chromosomal

the daughter cells will receive a flawed, mutant genome that will

grow uncontrollably like a cancer cell.

evenly throughout the cell cycle between successive mitoses. Instead,

S (synthetic) phase. S phase in mammalian cells usually takes 6-8

two sets of condensed chromosomes to opposite poles of the cell,

pinching off and separation of the two daughter cells.

phase during which time the recently divided cell prepares itself for S

phase. This long preparation period allows the cell to synthesize a

number of macromolecular constituents and build up mass. Cells that rush

or G1 phase of the cell cycle. Similarly, following successful

there is a long period of time - often 4-5 hours - when the cell

phase is the second gap phase in the cell cycle, termed its G2 phase. In

sum, the active cell cycle is divided into 4 phases: M, G1, S and G2;

phases of the cell cycle:

Control of the cell cycle

Few if any cells in the body commit themselves to passage

through the cell cycle on the basis of their own, autonomous, internally

generated decisions. A normal cell does not have a ''mind of its own''.

by extracellular signals. These signals encourage or discourage the

cell to grow and divide. Such dependence by a cell on extracellular,

integrity and function of a complex tissue. Each normal cell must

order to ensure that the community of cells as a whole behaves like a

Precisely how can we understand the control of a cell's

proliferation (growth and division) by its extracellular environment?

environment of a living tissue where a cell co-exists with a multitude of

cell types in the midst of a complex tissue architecture. Instead, we

are forced to study isolated cells growing in a culture dish, where we

can control cell number and define the extracellular environment of each

cell. More information on cell cultures is

Introduction to the 7.01 Hypertextbook

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Use of DNA in Identification

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success looking for protein differences, cell surface differences,

in principle it is possible to start from the DNA of a single cell and

Originally, simple HLA typing was used, typing of cell surface

outside the nucleus of the cell. It's a small bit of DNA, and what's

An Interview with DNA Forensics Authority Dr. Bruce Weir

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studies available. The FBI, Lifecodes, Cellmark, and other laboratories

Lab #2: Chromosome Mapping

meiosis Two successive nuclear divisions (with corresponding cell

cell.

recombinant An individual or cell with a genotype produced by

recombinant cells or individuals.

partially diplid cell that generates new gene or chromosomal

combinations not found in that cell or in its progenitors. (2) At

cells from a single meiosis.

Immunology Encyclopedia

B lymphocyte Type of leucocyte cells that are important in

B Cell Same as B lymphocyte

results in the activation of selected T-cell or

B-cell clones, resulting in an immune response.

clone Genetically identical cells or organisms produced from a

cytotoxic T cells Cells of the cellular

cells. (Contrast with helper T cells,

suppressor T cells.

helper T cells T cells that participate in

the activation of B cells and of other T cells; targets of the HIV-I

cytotoxic T cells,

suppressor T cells.)

inflammatory T cells (Th1)

lymphocyte A major class of white blood cells. Includes

T cells, B cells,

and other cell types important in the immune response.

phagocyte A white blood cell that ingests microorganisms by

suppressor T cells

T cells that inhibit the responses of B cells and

other T cells to antigens. (Contrast with cytotoxic T cells, helper T cells)

T cell A type of lymphocyte, involved in the

cellular immune response. The final stages of its development occur in

the thymus gland. (Contrast with B cell; see also cytotoxic T cell,

helper T cell, suppressor T cell)

Cell Basics

Cell Basics

Cell Basics

Cell hierarchy

Cell Elemental Composition

The cell is the fundamental unit of life. The cell theory,

Cells are the fundamental units of life, because a cell is the

All living things are made of cells.

viruses are only alive while infecting a cell.

cells

concentrate almost exclusively on the molecular through the cellular

Cell Elemental Composition

Cells are 90% water. Of the remaining molecules present, the dry

10% miscellaneous

Membrane Transport Mechanisms

It is of seminal importance to the cell that it be able to transport

better yet, a barrel when viewed from the outside of the cell, with each of the

This hole could be used to transport substances into the cell or out from the

cell. In fact, this hole can be a relatively hydrophilic environment if

cells utilize a wide range of transport mechanisms. The mechanisms fall into

the maximum possible concentration of the molecule inside the cell (or

outside the cell if it is a waste product). The effectiveness of diffusion

some substances (such as H2O), the cell must utilize other mechanisms for

molecules (which otherwise could not diffuse across the cell membrane) to

freely diffuse in a nd out of the cell. These channels comes into greatest

an antiport, it transports K+ into the cell and Na+ out of the cell at the

across the cell membrane, and then utilizing that gradient to transport a

across the cell membrane by using energy to pump protons out of the cell.

moving down its concentration gradient to transport lactose into the cell.

This coupled transport in the same direction across the cell membrane is

first step, generating a strong Na+ gradient across the cell membrane. Then

into the cell.

This system is used in a novel way in human gut epithelial cells. These cells

that the epithelial cells are joined together by tight junctions to prevent

first being filtered by the epithelial cells.

Examples of Viral Replication Pathways

In lysis, the host cell's membrane is damaged and the cytoplasm is able

to leak out. The cell dies rapidly, releasing virus particles.

host cell is not killed outright, but is occupied by the virus and used

cell, a new cycle of infection will begin.

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7.01Recombinant DNA Practice Problem

a) So that the DNA can be replicated, so that the daughter cells will

b) So that you can select for cells that carry the plasmid. This is for

iii) Ampicillin to select for cells with the plasmid. X-gal to

turn the lacZ+ cells blue. Lactose to induce the lac operon on the

cells can still grow).

Membrane Proteins

Cells are constantly pumping ions in and out through their plasma

is used by cells to drive the protein pumps in the brain that do nothing

else but transport ions across plasma membranes of nerve cells. How can

Cells contain proteins that are embedded in the lipid bilayer of their

extracellular medium, a hydrophobic domain in the middle of the amino

attached to their hydrophilic domains that protrude into the extracellular

membrane. A typical mammalian cell may have several hundred distinct

glycoproteins will have its extracellular domain glycosylated with a

extracellular space.

The 7.01 LINKS and WWW Tutorial

excellent place to start exploring the Web on your own.

3 Proteins

specific enzymes that compose a cell's metabolism. An E. coli

Check out the Amino Acid Repository, maintained by the Image Library of Biological Macromolecules, for an excellent summary of amino acid properties and great graphic images of the twenty amino acids.

Basic Virus Structure

Basic Virus Structure

instead of DNA). Viruses survive and reproduce by infecting a cell and

commandeering the cellular synthetic machinery to make more viruses. Then

the viruses lyse the cell and start the cycle over again.

Structure and Function of Organelles

Structure and Function of Organelles

Organelles are small structures within cells that perform dedicated functions. As the name implies, you can think of organelles as small organs. There are a dozen different types of organelles commonly found in

eukaryotic cells. In this course we will focus our attentions on only

to their role at a molecular level in the cell, and leave descriptive

cell biology for another course. For example, our interest in the mitochondrion lies in its ability to generate energy in a form that is

useful to the cell, and to that end we are interested in how the

their distribution in different cell types.

Follow this link to view an animal cell while

Follow this link to view a plant cell while

translated into protein. Protein synthesis is extremely important to cells,

and so large numbers of ribosomes are found throughout cells (often

that was endocytosed by a larger cell billions of years ago, but not

explanation to the development of eukaryotic cells, has additional

various locations in the cell and even to its exterior.

This organelle digests waste materials and food within the cell,

compartmentalization of the eukaryotic cell: the cell could not

descriptions of organelles, entitled The WWW Cell Biology Course .

extremely important components of the cellular system. They are the cell

membrane, the cytoplasm, and the cytoskeleton. The cell membrane is so

of the cell, and are spread randomly throughout the cytoplasm. We

Cell Biology Chapter

Cell Biology Chapter

Cell Biology Chapter Directory

Cell Basics

Cell hierarchy

Relative Sizes of Biological Objects

Cell Elemental Composition

cells

Cell Biology Practice Problems

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types of junctions between animal cells

7.012 Cloning Project: Agricultural Biotechnology

required for cells to be able to use OA as a carbon source. Its map is

resistance) to select for plant cells carrying the plasmid. Finally, it

Hypertextbook Chapters

Cell Biology

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ATP as the "energy currency" of the cell

oxidizing and reducing agents in cells, and how they are "recycled"

connection of the respiratory pathways with other metabolic pathways in the cell

Lwoff's Pathways - Viral Replication

Lwoff's Pathways - Viral Replication

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interferes with the cell's normal metabolism, causing the symptoms

Although the host cells remain infected, the host is a symptom-free

called the lytic pathway. They enter and inject a host cell with DNA,

inject their DNA into the host cell - but instead of taking over the

host cell and using it to make viruses, the injected DNA can become

inactive for some time, until the appropriate cellular event triggers

until the 1950s, when it was explored at the cellular level by Andre'

cells - no phage were released when the cells of a lysogenic culture

of single bacterial cells of Bacillus megaterium, a really large

around in droplets that contained only single cells, they were found

in the small colonies derived from single cells. Where did they come

culture in a droplet was being watched, a single cell in it would

Lwoff concluded that the host cells were not really entirely immune to

eventually killing the host, and releasing new phage when the cell

most of the bacterial host cells, the phage was in an inactive form.

cells in a lysogenic culture to enter the lytic pathway simultaneously

In lysis, the host cell's membrane is damaged and the cytoplasm is able

to leak out. The cell dies rapidly, releasing virus particles.

host cell is not killed outright, but is occupied by the virus and used

cell, a new cycle of infection will begin.

DNA Fingerprinting in Human Health and Society

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altered by surgery, a DNA fingerprint is the same for every cell,

DNA must be recovered from the cells or tissues of the body. Only a

familial Alzheimer's, sickle cell anemia, thalassemia, and many others.

Meiosis and Genetic Recombination

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Genetic recombination happens during meiosis, a special type of cell

division that occurs during formation of sperm and egg cells and gives

chromosomes other body cells have. Otherwise, the fertilized cell

Inside the cells that produce sperm and eggs, chromosomes become

sex cells. Each chromosome moves independently of all the others - a

of chromosome 1 that an egg cell receives in no way influences which

sperm cell is made. Thus, when a sperm fertilizes an egg, the

Mitosis

Mitosis

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Mitosis is the process by which cells divide. The parent cell has already duplicated its chromosomes , providing both daughter cells with a complete copy of

Solving Feedback Regulation Problems

b) Given that 3-phosphoglycerate is used by several other cellular pathways, while the other molecules

b) Given that 3-phosphoglycerate is used by several other cellular pathways, while the other molecules

Cloning Genes

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digestive tract. The bacterial cells divide very rapidly making billions

cell has inherited the human insulin gene sentence.

recombinant plasmid DNA is inserted into E. coli, the cell will be able

the next generation of E. coli cells in the process known as gene cloning.

MIT Biology Hypertextbook: Chemistry Review

A lower pH always means a higher concentration of H+. The biochemically useful ends of the scale are 1 M HCl, which is pH 0, and 1 M NaOH, which is pH 14. In general, cellular pH is approximately 7.2-7.4. It is very closely controlled in the cytoplasm of a healthy cell.

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cell cycle and basic cell cycle regulation

Prokaryotic Gene Regulation

src="graphics/minus.xbm"> cells to be unable to grow on lactose. The

could be added to a Lac- cell to make it a Lac+ cell (Bacterial

the lac genes of E. coli, they are only expressed when cells

keeps the cell from wasting energy when lactose is absent. (This is

a cell must produce both beta-galactosidase (the protein product of

product of the lac Y gene are required for the cells to grow on

protein product of the lac Z gene are required for the cells to grow

(i) Proteins can diffuse throughout the cell and act all over the

cell, far from the piece of DNA that

places in the cell, or acting on different pieces of DNA. In the lac operon,

DNA sites cannot diffuse throughout the cell and only act on the adjacent

proteins which can diffuse throughout the cell. Therefore the wild-type

You can't make full diploids, but you can make cells that are diploid for

in a cell which carries a small number of genes and is

replicated by the cell. The resulting partial diploid cells are called

product that can diffuse throughout the cell, so the

functional copies of the lac operon in the cells.

of lactose, these cells will be Lac.

cells are Lac.

Therefore b-gal levels will always be high and the cells will be

However, neither copy produces active permease, so the cells will be

E. coli

3 E. coli

larger than the smallest living cells, the mycoplasmas (Purves, Chapter

Immediately outside the plasma membrane is a cell wall about 10

nm thick, and projecting from the cell are flagella and pili. The

causing the cell to change its direction. An E. coli cell consists of

approximately l/500 as much DNA as is contained in a single cell of a

prokaryotic cell of E. coli makes thousands of specific proteins.

cells require about a day to go through a division cycle. Because of

quickly. One cell can become 8 in an hour, 512 in 3 hours, over a

Lipids

The lipids we'll be studying are phospholipids, the primary components of cellular membranes. Phospholipids are amphipathic; that is, they are both hydrophilic and hydrophobic. The "head" of a lipid moleule is negatively charged phosphate group and the two

micelles

Monoclonal Antibody Technology

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antibodies in the following way: We can obtain cells that produce antibodies

naturally; we also have available a class of cells that can grow continually in

cell culture. If we form a hybrid that combines the characteristic of

In monoclonal antibody technology, tumor cells that can replicate endlessly

are fused with mammalian cells that produce an antibody. The result of this

cell fusion is a "hybridoma," which will continually produce antibodies.

of cell, the hybridoma cell; antibodies produced by conventional methods, on

the other hand, are derived from preparations containing many kinds of cells,

permanently in cell culture. When myeloma cells were fused with

antibody-producing mammalian spleen cells, it was found that the resulting

hybrid cells, or hybridomas, produced large amounts of monoclonal antibody.

This product of cell fusion combined the desired qualities of the two different

types of cells: the ability to grow continually, and the ability to produce

Because selected hybrid cells produce only one specific antibody, they are

body's own cells as well, sometimes producing undesirable side effects such

Genetics: Introduction and Analyzing Crosses

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cells. These combine randomly in four different ways to form F2

MIT Biology Hypertextbook: Enzyme Mechanisms

reactions in cells. Not all proteins are enzymes, but most enzymes are

Membrane Proteins Introduction

Membranes are of crucial importance to life, because a cell must separate

It must keep out foreign molecules that damage or destroy the cells

However, while the cell must always abide by

Cells within the complex tissue of a multi-cellular organism also need

protozoan cell. Each of the cells in our tissues communicates with

dozens if not hundreds of other types of cells about a variety of

cells at distant sites in the body, and what other cells it should

Ironically, the intrinsic structure of cells creates a formidable

obstacle to these important processes of intercellular communication.

The cell shields itself behind its membrane, which is relatively

impermeable to most types of molecules. This barrier enables the cell

to create its own intracellular environment that is distinct and very

cell to inform itself on what is happening in the world outside.

Therefore, cells have two major types of membrane proteins :

The cell has therefore evolved an array of proteins to cope with these

Receptors

The receipt of informational signals by a cell is a complex task.

For this purpose, cells display an extraordinarily elaborate array of

information from the extracellular space and relay this information into

the cell through the plasma membrane . In effect, cell surface receptors act

as the antennae of the cell.

Mammalian cells like our own have wide and diverse types of

One class of well-studied receptors is involved in helping the cell determine

with the cell cycle , a cell determines whether or not it should grow from

factors, sometimes termed mitogens because they induce the cell to grow

stimulate a cell to enter into a round of growth and division.

GFs act by binding to cell surface GF receptors. Each type of GF

binds to the extracellular domain of its own specific receptor and conversely

will not bind to receptors for other growth factors. This extracellular

will only bind to the EGF receptor on the surface of cells but not to the PDGF

cell surface.

ligand . Other ligands besides growth factors may convey signals from cell

to cell through intercellular space. There are at least several hundred

distinct extracellular ligand such as a growth factor to its cognate receptor.

by a cell or cells specialized for its release.

extracellular domain of its cognate receptor is only the beginning of the

plasma membrane into the cell? Such transmission of information by a

GF factor receptor proteins. Outside the cell, they have a ligand-binding N-

extracellular domain of the receptor encounters and binds a GF ligand. In

distinguish them from many other protein kinases throughout the cell that

The GF ligand binds to the extracellular domain of its receptor.

They then proceed to send signals further into the cell in a manner that

ultimately results in the cell growing and dividing.

(physically transported) into the cell in order for this transmembrane

while the ligand is still in the extracellular space.

outside the cell causes tyrosine kinase activation inside the cell. A number

surface of a given cell. Second these receptor molecules, while tethered in

extracellular domain in turn drags the cytoplasmic domains of the two

cytoplasmic substrate proteins that then pass signals further into the cell.

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cells of the immune system: B cells and T cells

humoral vs. cellular immune response

Culturing cells in vitro

Culturing cells in vitro

Culturing cells in vitro

Culturing cells in vitro

The propagation of mammalian cells outside of the living body in

process is also termed tissue culture. Most cells grow poorly outside

the conditions that cells see when they thrive in the confines of a

vitro culturing techniques involves connective tissue cells, termed

fibroblasts. These cells are responsible for generating most of the

connective tissue in the body, including tendons, fat cells, cartilage

vitro. Other cell types, such as epithelial cells that cover the

grow in culture. An exception is provided by the epithelial cells of the

addition, the cell requires glucose for energy, oxygen (coming from the

This collection of components provided to the cell, termed in

tissue culture medium will not encourage a cell to grow; more than these

the culture medium in order for cells to grow in vitro is blood serum, usually

that induce a cell to grow. These stimulants are termed growth factors or

100 amino acids. They are adsorbed to the surface of cells, attaching to

specific cell surface proteins that are termed growth factor receptors.

of many different cell types. Recall that the function of such a

across the plasma membrane into the cell interior, informing the cell

that an encounter has taken place with an extracellular growth factor.

the surface of a cell, a growth factor will only bind to its own cognate

cells will undertake a program of growth and expansion, doubling

components of the serum are exhausted or depleted. Cells that are placed

concentration, will rapidly exit the cell cycle and enter into the G0,

quiescent state. A population of serum-starved cells will sit quietly

to these cells, they will resume growth by re-entering the cell cycle.

Analogously, when growing cells deplete the growth-stimulatory factors

from the serum, they will exit the cell cycle even though nutrients

controllers - of the fate of the cell. How can we rationalize the

clotting, the acellular part of the blood is termed plasma, after the

serum. During the clotting process, platelets (the small, anuclear cell

encourage cell growth at the site of wounding as part of the wound

growing in vitro. In summary, in the absence of growth factors, cells

will exit the cell cycle into G0. In their presence, cells will pass

cell during the first half (or two-thirds) of the G1 phase of its growth

cycle. Thereafter, the cell, having received stimulation by these

later, cancer cells relate to their extra-cellular environment in a very

absence of extracellular stimulatory cues provided by growth factors.

factors. In effect, the growth of cancer cells is driven by their own

independence enables these cells to grow in a fashion that disregards

Intracellular controls on cell cycle progression: We confront an

describe the cell's growth program. Once the cell is induced to enter

requirements for extracellular growth factors are only the first of many

requirements that must be fulfilled. Before the cell enters S, it

that-are required to execute entrance into S. Moreover, the cell checks

that its DNA sequences are in order. In the event that the cellular DNA

has been damaged by some mutagen, the cell will pause in late G1 to

proceeds into S to copy its DNA. In doing so, the cell minimizes the

genome. By the same token, cells will not go into G2 and M until all of

their DNA has been replicated. Thus, there is an intracellular monitor

In addition, cells have a very effective, but poorly understood defense

next cell cycle.

Chemical Energetics

How is energy made available in cells? In what

When a cell needs to make a reaction go in an energetically unfavorable

still exergonic. Here, to carry out the reaction the cell uses a

Cells use similar mechanisms to make all sorts of energetically

Since the chemical machinery of the cell is driven by substances with

substances be made? Cells use only two kinds of energy:

Cells do not use thermal or electrical energy because they don't have

potentials in the membrane of nerve cells and fibers.)

How can we measure the energetic budget of a cell? The change Delta G in

positive and energy is required. In living cells this energy comes from

Solving Chemical Equilibrium Problems

energy for all cells. It begins with the following transformation which

Theoretically, the cell could phosphorylate glucose directly with

c) In a typical cell, glucose and phosphate are maintained at

concentration of Glucose-6-Phosphate if the cells used the reaction as

cell could not make practical use of such an unfavorable reaction.

e) The cell actually accomplishes the phosphorylation of glucose by

g) The concentration of Glucose-6-Phosphate typically found in cells is

glucose-glucokinase complexes in a cell when the concentration of

1.1 Membrane Structure and Composition

Biological membranes are bilipid layers . In a real cell the membrane

around the cell. However, they are often represented two-dimensionally

The phospholipids can move to the opposite side of a bacterial cell membrane

The

WWW Cell Biology Course. NOTE: Once you go to the WWW Cell Biology Course

membrane more fluid. Therefore, one way for a cell to control the fluidity

of its membrane is by regulating its level of cholesterol in the cell

Another way for the cell to control the fluidity of its membrane is to

G Protein Receptors

variety of biological signalling functions. Receptors on the cells

the cells of our olfactory bulbs in our nose convey information about

yeast cells communicate their sexual identity to each other by release

of polypeptide mating factors. The cell surface receptors that recognize

blood stream and adsorbs to specific receptors on the surfaces of cells

muscle cells to break down glycogen and release resulting glucose into

the surface of a variety of cell types throughout the body. This beta

embedded in the plasma membranes of these cells. As is the case with the

internalized into the cell. Instead, while bound for a short period of

signals into the cell cytoplasm. Serpentine receptors like the beta

G protein will send signals further into the cell. However, the G

Once made, the cAMP molecules act as intracellular glycogen, the high cAMP concentrations enable A kinase to

modify hundreds of target molecules in the cell.

Characteristics of Prokaryotes and Eukaryotes

There are two general classes of cells: prokaryotic and eukaryotic. The evolution of prokaryotic cells preceded that of

eukaryotic cells by 2 billion years.

beer ferment, is an example of unicellular eukaryotes.

Humans, of course, are an example of multicellular eukaryotes.

The major similarities between the two types of cells (prokaryote and

freely around the cell; the DNA of eukaryotes is held within its

higher levels of intracellular division of labor than is possible in

prokaryotic cells. Additional obvious differences between prokaryotes

Eukaryotic cells are, on average, ten times the size of

prokaryotic cells.

Cell Wall

Prokaryotes have a cell wall composed of peptidoglycan, a single

large polymer of amino acids and sugar . Many types of eukaryotic cells

also have cell walls, but none made of peptidoglycan.

Membrane Transport Problem Answers

If X is transported into the cell by passive diffusion or

in the cell will never become higher than [X] outside.

active transport can make the concentration of X inside the cell higher

than it is outside and requires energy. If the cell is deprived of

mitochondrial proton gradient so the cell can no longer make ATP)

epithelial cell from the lumen of the gut? What is the key

intestinal epithelial cells. The energy to transport glucose up its

(Na+) out of the cell and two potassium ions (K+) in. Effectively, the

through an intrinsic protein and into the cell.

cells, even though this involves moving Ca++ up its concentration

the cell could bind to the carrier protein. ATP could bind to the ATPase

conformational changes that release Ca++ to the outside of the cell. ADP

In your studies of some cells, you discover a new protein, esgfun.

Esgfun has an extracellular domain A and an intracellular domain C. You

you observe the Jane cells, portion A of esgfun always faces the

extracellular fluid and portion C always faces the cytoplasm.

across the cell membrane. This is because of the thermodynamics

Neurons and other excitable cells have membranes that are

that the inside of the cell is negative with respect to the outside.

cell for each 2 K+ in. (using ATP as an energy source to pump both these

concentration gradient such that there is high [Na+] outside the cell,

and high [K+] inside the cell.

further net ion flow. For example, K+ will leak out of a cell since

positive ions leaves the inside of the cell negative with respect to the

outside. Eventually, there is enough negative charge inside the cell

cell, and low [Cl-] inside.

leaving the inside of the cell negative. (Note that during an action

other in the extracellular fluid.

Based on your knowledge of transport across cell membranes, propose

epithelial cells. Include a diagram of your mechanism. (There are

The Cytoskeleton

The Cytoskeleton

left out of drawings of the cell, but it is an important, complex, and

dynamic cell component. The cytoskeleton maintains the cell's shape,

anchors organelles in place, and moves parts of the cell in processes

(see diagram on pg. 82 of Purves) and are often used by cells to hold

microtubule, and are often used by cells to change their shapes as

are cellular motors, such as myosin (an motor that moves along actin

Cytoskeletal components are also critical for the process of cell

Southerns, Northerns, Westerns, & Cloning: Molecular Searching Techniques

These are techniques for analyzing cellular macromolecules: DNA,

These techniques are necessary because a cell contains tens of

of different proteins. When the cell is broken open to extract DNA, RNA,

or protein, the result is a complex mixture of all the cell's DNA, RNA,

the molecule of interest from the complex mixture of cellular components

total cellular RNA, or total cellular protein would look like in a gel

blots. Usually, the solid support is a sheet of nitrocellulose paper

(sometimes called a filter because the sheets of nitrocellulose were

used. DNA, RNA, and protein stick well to nitrocellulose in a

The DNA, RNA, or protein can be transferred to nitrocellulose in

the target molecules. Because the nitrocellulose is absorbent, some of

At this point, you have a sheet of nitrocellulose with spots of probe

1) Isolate genomic (chromosomal) DNA from human cells.

4) Press a piece of nitrocellulose onto each master plate and lift off.

promoter and an ATG codon. Cells containing these plasmids will produce

Polymerase Chain Reaction - Xeroxing DNA

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this process, only it does it in a test tube. When any cell divides,

it started. So the cell has another enzyme called a primase that

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roles of membranes in eukaryotic cells

Solving Problems

nitrocellulose. You have a cDNA for the R gene which you use as a

per cell. They are the same intensity as the bands from the RR and rr

identical copies per cell.

cell. They are lighter and thinner than the other bands because there is

Feedback Inhibition

major molecules in cells: nucleotides, amino acids, sugars, and lipids.

an excess of E in the cell, E (or a byproduct of E) will inhibit enzyme

2, preventing it from converting any more B to C. In this way, the cell

3.5 Solving Enzyme Kinetics Problems

of cells is small so that the sucrose concentration does not change

the breakdown of a component of the cell wall of certain bacteria, causing

{But why then do bacteria use an unstable molecule as a cell wall?

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mechanisms of B-cell activation