Cell Communication and Cell Cycle

Endocrine

Long distance signaling in the circulatory system

Autocrine

Self signaling

Juxtracrine

Signals affect only adjacent cells

Paracrine

Short distance signaling between cells

When a response occurs in a cell, what is needed to stop it?

Ligand needs to detach or amount of ligand needs to decreases

What are gap junctions?

Small tunnels that connect cells, facilitating the movement of small molecules and ions between animal cells.

What are plasmodesmata?

Small tunnels that connect cells, facilitating the movement of small molecules and ions between plant cells.

What are local regulators?

Messenger molecules that travel only short distances

What is synaptic signaling?

A signal moves along a nerve cell which triggers the secretion of neurotransmitter molecules

In what type of signaling are hormones used?

Long distance (endocrine)

What is another name for endocrine signaling?

Hormonal signaling

What occurs in hormonal signaling?

Specialized cells release hormone molecules that travel via the circulatory system

Who discovered how the hormone epinephrine acts on cells?

Earl W. Sutherland

What are the three processes in cell signaling Sutherland suggests?

• Reception, detection of the signal

• Transduction, conversion of the signal to a cellular response, via a signal transduction pathway

• Response, a cellular activity in response to the signal

What is a ligand?

A signaling molecule

What type of bond do the ligand and receptor create?

A highly specific bond

Ligand binding generally causes what to happen to the receptor?

Shape change occurs

What are most receptors activated by?

The shape change in its structure initiated by a ligand

What type of proteins are most signal receptors?

Plasma membrane proteins

What are the two main type of membrane receptors?

G protein-coupled receptors (GPCRs) and ligand-gated ion channels

What protein works with GPCRs?

G protein

What molecule does G protein bind to?

GTP

How do ligand gated ion channels act?

As a "gate" for ions when the receptor changes shape

What may get triggered by the diffusion of ions through open channels?

An electric signal

Where are intracellular receptor proteins found?

The cytoplasm or nucleus of target cells

What type of molecules can readily cross the membrane and activate receptors?

Small or hydrophobic chemical messengers

Name examples of hydrophobic messengers

Steroid and thyroid hormones of animals and nitric oxide (N O) in both plants and animals

What is phosphorylation?

Transfer of a phosphate group to ATP using protein kinase

What is a phosphorylation cascade?

A type of signal transduction pathway where phosphorylation occurs, then protein phosphatases remove the phosphates, in a continuous pattern adding a phosphate and then taking it off.

What changes the form of a protein from inactive to active?

The addition of phosphate groups

What do protein phosphates do?

Remove the phosphates from proteins

What is dephosphorylation?

Removal of phosphates from proteins, initiated by protein phosphatases

What do protein phosphatases provide a mechanism for?

Turning off a signal transduction pathway

What is a pathways "first messenger"?

The ligand

What are second messengers?

Small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion

What are two common second messengers?

Cyclic AMP (cAMP) and calcium ions (CA2+)

What converts ATP to cAMP?

Adenylyl cyclase

What is the immediate effect of cAMP?

The activation of protein kinase A, which then phosphorylates a variety of other protiens

Where may the response occur?

In the cytoplasm or nucleus

Describe positive feedback pathways

• Cell communication: Endocrine

• Example of use: Breastfeeding

• Explanation: Effector makes initiation event stronger

Describe negative feedback pathways

• Cell communication: Paracrine

• Example of use: Insulin production to lower blood sugar

• Explanation: Stimulus is reduced by the effector

Describe humoral immune response

• Cell communication: Autocrine

• Example of use: When foreign material (antigens) are detected in the body

• Explanation: Signal (antigen) is digested into cytokinesis and T-cell creates antibodies

Describe cell mediated immune response

• Cell communication: Cell to cell endocrine

• Example of use: When body is infected with a virus or bacterium

• Explanation: Infected cells get killed by multiplying killer T-cells

Describe neurotransmitters

• Cell communication: Paracrine

• Example of use: To help you move your limbs, feel sensations, and keep your heart beating

• Explanation: Calcium reaches vesicles to release neurotransmitters then neurotransmitters are sent to the nucleus of nerve cells through the axon

Describe plant responses (hormones, tropisms)

• Cell communication: Paracrine

• Example of use: To sense the change of season

• Explanation: Regular process (ligand to receptor to response) and regulates growth

Describe morphogens, embryonic development

• Cell communication: Long-distance signaling (paracrine)

• Example of use: To regulate cell fate specification and tissue patterning during embryonic development

• Explanation: Morphogen binds to transmembrane receptor, then signal transduction allows message to enter the nucleus

What is a genome?

All the DNA in one cell of an organism

What are DNA molecules packaged into?

Chromosomes

What is chromatin?

A complex of DNA and protein

What are somatic cells and how many chromosomes do they have?

Non-sex cells, 46

What are gametes and how many chromosomes do they have?

Sex cells, 23

What do chromosomes look like when a cell is not dividing?

Long, thin chromatin fiber

What happens in preparation for cell division?

DNA is replicated and the chromosomes condense

What is a sister chromatid?

One half of a duplicated chromosome

What is a centromere?

The point on a chromosome where the chromatids are most closely attached

What are the stages of cell division and what occurs in them?

• Mitosis: the division of the genetic material in the nucleus

• Cytokinesis: the division of the cytoplasm

How are gametes produced?

Meiosis

What is the result of meiosis?

4 haploid daughter cells

What are the five phases of the cell cycle in order?

Interphase, prophase, metaphase, anaphase, telophase

In what process does cytokinesis occur in animal cells?

Cleavage which forms a cleavage furrow, a shallow groove in the cell surface

What forms during cytokinesis in plant cells?

Cell plate

What is binary fission?

A form of asexual reproduction in which the parent divides into two approximately equal parts

What occurs during binary fission in bacteria?

The single chromosome replicates beginning at the origin of replication. The two daughter chromosomes actively move apart as the cell elongates, and the plasma membrane pinches inward, dividing the cell into two

What did mitosis evolve from?

Binary fission

Certain protists exhibit what type of cell division?

Some sort of intermediate between mitosis and binary fission

What is the cell cycle driven by?

Specific signaling molecules present in the cytoplasm

What directs the sequential events of the cell cycle?

The cell cycle control system

What is the cell cycle control system regulated by?

Internal and external controls

What occurs in a cell if the cell cycle control system does not give cell division the go ahead after G1?

Cell goes into non-dividing state called G0

What is a reason anaphase would not begin?

If any kinetochores remain unattached to spindle microtubules

What does attachment of all kinetochores activate?

A regulatory complex

What are growth factors?

Proteins released by certain cells that stimulate other cells to divide

What is density-dependent inhibition?

When crowded cells stop dividing

What is anchorage dependence?

The need for cells to be in contact with a solid surface to divide

Cells in culture that can divide indefinitely are said to have undergone what process?

Transformation

What do malignant tumors undergo?

Metastasis, exporting cancer cells to other parts of the body where they may form additional tumors

What are the 3 stages of interphase?

G1, S, G2

What are mitosis and cytokinesis considered?

Mitosis phase

What occurs in G1?

Cell performs normal functions, gets bigger, protein synthesis and respiration occur, cell grows by producing more proteins and organelles

What occurs in S phase?

DNA replication

What occurs in G2 phase?

Chromosomes start to condense, organelles duplicate, centrioles form, cell prepares to divide with the division of centrosomes

What occurs in prophase?

Centrioles move to opposite poles forming spindle fibers, nuclear envelope begins to break

What occurs in prometaphase?

Sister chromatically have joined to spindle fibers

What occurs in metaphase?

Chromosomes line up in the middle of the cell

What occurs in anaphase?

Spindle fibers pull sister chromatids apart

What occurs in telophase?

Cell begins to reform (nucleolus and nuclear envelope), spindle fibers break down

What occurs in cytokinesis?

Cleavage forms cleavage furrow in animal cells, cell plate forms in plant cells

What is nondisjunction?

Chromosomes don't separate properly during cell division

What is apoptosis?

Programmed cell death