AP Bio Unit 4: Cell Communication and Cell Cycle

Types of signaling

Juxtacrine, autocrine, paracrine, endocrine

Juxtacrine

direct contact

Autocrine

targets self

Paracrine

local/ nearby

Endocrine

long distance

Juxtacrine signaling (immune system)

Ligand on one cell binds with a receptor on another

Juxtacrine signaling (gap junctions, plasmodesmata)

Cells share particles through small pores that link their cytoplasms together

Local (paracrine) signaling

Cells secrete ligands to nearby cells where they initiate a response. ex: neurotransmitters (synapses)

Long distance (endocrine) signaling

1. Produce ligands called hormones

2. Hormones travel through bloodstream to target cells

3. Slower but a long-lasting effect

Steps of cell signaling

1. reception

2. transduction

3. response

Reception

Binding between signal molecule (ligand) + specific receptor. Receptor protein changes shape and initiates a transduction signal.

Membrane surface receptors

for ligands that can’t pass through (hydrophilic or very large)

Intracellular receptors

for small or hydrophobic ligands that can pass through the membrane

Transduction

Conversion of signal reception into cellular response. Second messengers are triggered to amplify the signal (ex: cAMP). Creates a cascade that mobilizes many more molecules.

Kinases

enzymes that phosphorylate other molecules and activate them

Phosphorylation cascade

occurs during transduction and amplifies the signal

Phosphorylation

addition of a phosphate group to one or more sites of a protein. acts as a switch.

Cyclic AMP (cAMP)

small molecule made from ATP. used as a second messenger.

G-coupled protein receptors

Response

Signal transduction pathways lead to regulation of cellular activities. Occurs in the nucleus and cytoplasm. Many pathways regulate the synthesis of enzymes or other proteins by turning genes on/off in the nucleus.

G proteins (guanine nucleotide-binding proteins)

act as molecular switches in cells. transmit signals. bind the GTP and GDP.

Ligand-gated channels

These proteins act as both receptors and channels. When the appropriate ligand is bound, solutes are allowed through the protein channel.

Enzyme and enzyme-linked receptors

These receptors are either enzymes or enzyme linked proteins (interact directly with enzymes). Trigger the intracellular production of second messenger cyclic GMP. ex: tyrosine kinase (TK) receptors.

Nitric oxide (NO)

gas that acts as a ligand

Peptide (protein) ligands

largest and most diverse class of water-soluble ligands. ex: growth factors, insulin, certain neurotransmitters.

Apoptosis

programmed cell death

Cell division purpose

repair, replace cells, growth, immune response (B and T cells), asexual reproduction

Mitosis

process of replicating the nucleus before a parent cell divides into two identical daughter cells. Short phase of cell cycle. Results in two nuclei, not two cells.

Chromosomes

molecules of DNA. Compact and organized in eukaryotes. DNA is tightly wrapped around proteins. Each has millions of base pairs and thousands of genes.

Chromosome structure

Chromatin

the name of the material made from DNA and protein

Gene

segment of DNA that codes for a specific trait

Single chromatid chromosome (unduplicated)

Double chromatid chromosomes

Chromatid

a chromosome copy

Number of centromeres equals

number of chromosomes

Interphase (chromosome numbers)

Before interphase occurs there are 46 chromosomes and after interphase duplication there are still 46 chromosomes but they each have two chromatids (or two copies of information). There are 92 chromatids after duplication.

Two identical chromatids

one is an exact copy of the other and each contains one DNA molecule

Centromere

constricted point of the chromosome

DNA molecule

long string like DNA molecule formed into a compact structure by proteins called histones

Cell cycle phases

1. Interphase - cell grows, DNA replicated

2. Nuclear division - mitosis

3. Cell division - cytokinesis

Interphase

majority (90%) of cell’s life

Interphase phases

1. Gap 1 (G1)

2. S phase

3. Gap 2 (G2)

Gap 1

most growth occurs, organelles replicate, cell makes proteins and enzymes for replication

S phase

DNA replicates (single chromosomes become double)

Gap 2 (G2)

more cell growth, DNA checked for errors and repaired, final prep for mitosis

G0

the phase in the cell cycle in which the cell is neither dividing nor preparing for division

Mitosis and cytokinesis

Prophase

Chromosomes condense and become visible, chromosomes appear as two sister chromatids held together at the centromere, nuclear envelope breaks down

Kinetochores

protein structures that allow microtubules to attach to the centromere

Metaphase

All chromosomes are aligned at equator of the cell (______ plate), chromosomes are attached to opposite poles and are under tension

Anaphase

Sister chromatids are separated, chromatids are pulled by microtubules to opposite poles

Telophase

Nuclear envelope reforms, nucleolus reforms, spindle breaks down, chromosomes uncoil, cytokinesis begins, 2 identical nuclei formed by the end

Cytokinesis

division of cytoplasm. forms two identical cells. cell plate (dividing cell wall) forms in plant cells.

Cell cycle checkpoints

G1, G2, M (Mitotic)

Cyclins

proteins that control cell cycle checkpoints. increases in the concentration of _____ proteins are triggered by both external and internal signals. turn on Cdks.

Cyclin-dependent kinases (Cdks)

phosphorylate other proteins that advance the cell cycle past a checkpoint

Cell cycle negative control

Some regulatory pathways halt the cell cycle. ex: p53 tumor suppressor protein

p53 tumor suppressor protein

If damaged DNA is detected before G1, it halts the cell cycle and recruits enzymes to repair the DNA (activates Cdk inhibitor, cyclin complex inactivated). Can trigger apoptosis to prevent replication.

Cell cycle loss of control

mutations of regulatory genes can lead to uncontrolled cell growth and possibly cancer

Tumor

a mass of irregular cells

Benign tumor

cells grow only locally and cannot spread by invasion or metastasis

Malignant (cancer) cells

invade neighboring tissues, enter blood vessels, and metastasize to different sites

Metastasis

when cancer spreads via the blood or lymphatic system

Contractile ring (animals)

cell division occurs when a band of cytoskeletal fibers contract inward and pinch the cell in two. The indentation produced as it contracts inward is called the cleavage furrow.

Examples of cells in G0

neurons that conduct signals, liver cells that store carbohydrates

24 hours

cell cycle length (typical, human cells)

Mitotic spindle

forms in prophase. made of microtubules, strong fibers that are part of the cell’s “skeleton”. it organizes the chromosomes and moves them around during mitosis. grows between the centrosomes.

Prophase condensation

makes it easier to pull apart chromosomes

Spindle checkpoint

before anaphase, cell checks that all chromosomes are at the metaphase plate with kinetochores correctly attached to the microtubules

Motor proteins

molecular machines that can “walk” along microtubule tracks and carry chromosomes or other microtubules

broken down, reappear, decondense

In cytokinesis, the mitotic spindle is _____, nuclear membranes and nuclei _______, and chromosomes ______

Genome

a cell’s set of DNA

Histones

a group of basic (positively charged) proteins that form “bobbins” around which negatively charged DNA can wrap

Negative

charge of DNA

Positive

charge of histones

Decondensed

chromatin is ______ for most of the life of the cell and exists and long, thin strips. Can be easily accessed by proteins and other cellular machinery when in this state.

Circular

bacterial chromosomes are typically…

Cohesins

sisters chromatids are attached by proteins called…

G1 Checkpoint

checks for:

• cell size - large enough?

• nutrients - enough energy?

• growth factors/molecular signals - receiving positive ques?

• DNA damage - is any DNA damaged?

G2 Checkpoint

Checks for:

• DNA damage - is any DNA damaged?

• DNA replication - DNA completely copied during S phase?

M checkpoint

spindle checkpoint is also known as…

Types of cyclins

G1, G1/S, S, and M cyclins. Promotes the events of each phase.

Maturation-promoting factor (MPF)

adds phosphate tags to several different proteins in the nuclear envelope, resulting in its breakdown. activates targets that promote chromosome condensation and other M phase events.

Anaphase-promoting complex/ cyclosome (APC/C)

causes M cyclin destruction which takes the cell out of mitosis