unit 4: cell communication and cell cycles Flashcards
What is a signal transduction pathway?
The chains of molecules that relay signals inside a cell
How does yeast mating serve as an example of a signal transduction pathway?
Yeast cells identify their sexual mates by chemical signaling. When exposed to each other’s mating factors, a pair of cells of opposite type change shape, grow toward each other, and fuse. The new cell contains all the genes of both original cells, a combination of genetic resources that provides advantages to the cell’s descendants.
Local signaling types
paracrine: signaling molecules are secreted by the signaling cell. some molecules only travel a short distance
synaptic: an electrical signal along a nerve cell that triggers the secretion of neurotransmitter molecules. nerve cell releases molecules into synapse and stimulates the target cell (mouse party)
long distance signaling
endocrine: specialized endocrine hormones into body fluids (often blood). specialized cells release circulatory travelling hormones. plant hormones/growth regulators sometimes travel in a vessel but often diffuse as gases (think ripening fruit gas)
Signal Transduction: Reception
a signal is detected when the chemical signl (or ligand) binds to a receptor protein on the surface of the cell or inside the cell
signal transduction: transduction
the transmission of molecular signals from a cell’s exterior to its interior
signal transduction: response
the cell’s response to their environment, communication with other cells, next steps, etc
ligans
a molecule that binds specifically to another molecule. generally causes a receptor protein to undergo a change in shape
G Protein-linked receptor
G proteins function as a molecular switch. When GDP is bound, the protein is inactive. With GTP bond, the protein is active and often works with another protein (usually an enzyme)
G Protein-Linked receptor process
ligand binds to receptor. receptor changes shape and activates G protein as GTP displaces the GDP molecule. the activated g protein dissociates from the receptor, diffuses across the membrane and binds to an enzyme. this changes the ENZYMES shape now and leads to a cellular response. G proteins also function as a GTPase enzyme. it turns GTP back to GDP and inactivates the G protein and enzyme once the protein has done its work.
A G protein is also a GTPase enzyme. Why is this important?
The GP hydrolyzes its bound GTP to GDP and Phosphorous base (step 4). This makes the GP inactive again and everything is available for reuse. The GTPase function allows the pathway to shutdown rapidly when the signaling molecule isnt present.
The second type of receptor described is receptor tyrosine kinase. Explain what a kinase enzyme does.
Kinase enzymes catalyze the transfer of a phosphate group from a donor ATP molecule to a substrate.
Explain what a kinase enzyme does.
Kinase enzymes catalyze the transfer of a phosphate group from a donor ATP molecule to a substrate.
- How does tyrosine kinase function in the membrane receptor?
They are membrane receptors that attach phosphates to tyrosine. They catalyze the transfer of a phosphate group from ATP to the amino acid tyrosine of a substrate protein.
Intracellular receptors are found in the cytoplasm or nucleus of the cell, where they bond to chemical messengers that are hydrophobic or very small, like nitric oxide.
Although cell-surface receptors represent 30% of all human proteins, they make up only 1% of proteins whose structures have been determined by x-ray crystallography.
Difference between first and second messengers
First messenger is the ligand while the second is any small non-protein component of a signal transduction pathway (such as Calcium ion or cAMP that relays a signal to a cell’s interior in response to a signaling molecule bound by a signal receptor.)
When cell signaling causes a response in the nucleus, what happens?
mRNA is transcribed and a protein is synthesized
When cell signaling causes a response in the cytoplasm, what happens?
signaling pathways may regulate the activity of proteins, affecting those that function outside of the nucleus. A signal may close or open an ion channel or change a cell’s metabolism
ligand-gated ion channels and voltage-gated ion channels
They are especially important in the nervous system. The neurotransmitter molecules released at a synapse between two nerve cells bind as ligands to ion channels on the receiving cell which causes the channels to open. Ions flow in or out and trigger an electrical signal that propagates down the length of the receiving cell.
process of apoptosis
dna is chopped up, the cell shrinks and becomes lobed, the cell parts are packed in vesicles and digested by scavenging cells.
three key roles of cell division
asexual reproduction
growth and development
tissue renewal
cell cycle
the life of a cell from the time it is first formed during the division of a parent cell until its own division into two daughter cells
genome
a cell’s DNA or genetic information. prokaryotic genomes are often a single DNA molecule vs eukaryotic genomes are several sets
Define the following terms: chromosome, chromatid, centromere, chromatin
Chromatin: contains code that controls cell; made of proteins
Chromatid: one of the two identical halves of a chromosome that has been replicated in preparation for cell division
Chromosome: condensed form of chromatin (DNA Molecules)
Centromere: region of attachment between sister chromatids
Mitosis
the division of the genetic material in the nucelus. follows interphase and comes before cytokinesis
mitosis vs meiosis
By what process are the damaged cells in a wound replaced?
Meiosis By what process are eggs formed?
By what process does a zygote develop into a multicellular organism?
In which process are identical daughter cells produced?
Which process reduces chromosome number of daughter cells?
mitosis
meiosis
mitosis
mitosis
meiosis
G1
the growth phase of the cell cycle consisting of the portion of interphase before DNA synthesis (replication) begins. cell grows and continues normal functions
S
the synthesis phase of the cell cycle, DNA replication
G2
the second growth phase, the cell continues growing and prepares for division
prophase
early mitotic spindle forming
chromatin condense into chromosomes
prometaphase
spindles attached to centrioles
kinetochores
more centrosomes
nuclear envelope leaves
centrosomes approach poles
metaphase
chromosomes lined up at metaphase plate
centrosomes reach the poles
anaphase
chromosomes now split and pulled to opposite poles
telophase
cleavage furrow!!!
nuclear envelope reforms
each cell has centrosome with centrioles
mitotic spindle:
forms during prophase; made out of microtubules; controls chromosome movement
aster
radical array of short microtubule organizing center; extends from each chromosome
what happens at checkpoints
G1- most important checkpoint. If go, cell continues the cycle. If stop, cell enters G0. It is regulated by the cyclin-CDk complex
G2- if go, it allows the cell to proceed into anaphase; When sufficient MPF accumulates, he G2 checkpoint is passed, and mitosis is promoted
M- if stop, that means that one of the chromosomes isn’t attached to a spindle. The kinetochore must all be attached to the spindle fibers during metaphase. This will activate sepaarse which allows the chromatids to separate and anaphase will proceed.
protein kinase
An enzyme that regulates the biological activity of proteins by phosphorylation of specific amino acids with ATP as the source of phosphate, making a protein activated.
Distinguish between a benign tumor and a malignant tumor.
Benign- mass of abnormal cells with specific genetic and cellular changes such that the cells are not capable of surviving at a new site and generally remain at the site of the tumor’s origin.
Malignant- a cancerous tumor containing cells that have significant genetic and cellular changes and are capable of invading and surviving in new sites. Malignant tumors can impair the functions of one or more organs.
Maturation promoting factor
is a cyclin CDK complex that triggers a cell’s passage past G2
internal signals
microtubules send a molecular signal, delaying anaphase ;
kinetochores not attached to spindle
external signals
certain cells that stimulate other cells to divide
platelet-derived growth factor stimulates the division of human fibroblast cells in culture
density-dependent inhibition where crowded cells stop dividing
proto oncogenes
normally activates cell division
growth factor genes
become oncogenes when mutated
(cancerous)
switched on = cancer!
tumor-suppressor genes
normally inhibits cell division
switched off = cancer!
