Unit 4 Cell and Molecular Biology

hormone

a signal that is sent to most cells throughout a multicellular organism

Delta is an inhibitory signal involved what kind of signaling

contact dependent

paracrine

acts on nearby cells

paracrine signalling example

the regulation of inflammatory responses at the site of an infection

example of extracellular signal molecules

nucleotides and amino acids

Signal molecule characteristics

• can bind directly to intracellular proteins that bind DNA and regulate gene transcription

• can be transmembrane proteins

all members of the steriod hormone receptor family

interact with signal molecules that diffuse through the plasma membrane

acetylcholine and heart muscle, salivary gland, and skeletal muscle cells

• heart muscle cells decrease their rate and force of contraction when they receive acetylcholine whereas skeletal muscle cells contract

• active AC receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways

• all respond to AC within milliseconds to minutes of receiving the signal

the local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by

diffusing into cells and stimulating the cyclase directly

Hydrophilic extracellular signal molecules

must bind to a cell surface receptor so as to signal a target cell to change its behavior

molecular switches characteristics

• Protein kinases transfer the terminal phosphate from ATP onto a protein.

• Serine/threonine kinases are the most common types of protein kinase.

• A GTP-binding protein exchanges its bound GDP for GTP to become activated.

Foreign substances like nicotine, morphine, and menthol exert their initial effects by

Interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus.

Which of the following happens when a G-protein-coupled receptor (GPCR) activates a G protein.

The α subunit exchanges its bound GDP for GTP.

GPCR characteristics

• are the largest family of cell-surface receptors in humans.

• are used in endocrine, paracrine, and neuronal signaling.

• are found in yeast, mice, and humans
  

The length of time a G protein will signal is determined by

the GTPase activity of Gα

Cholera and whooping cough both are caused by bacteria that:

alter the function of G proteins.

small intracellular signaling molecule examples

• cyclic AMP

• inositol triphosphate

• Diacyglycerol

Another name for small intracellular messenger molecules is:

second messengers.

When activated by a GPCR, adenylyl cyclase:

converts ATP to cAMP.

The enzyme cyclic AMP phosphodiesterase helps terminate a response mediated by an increase in cyclic AMP by:

converting cyclic AMP to AMP.

How does IP3 function in the inositol phospholipid pathway?

It binds to and opens Ca2+ channels that are embedded in the ER membrane, releasing Ca2+ into the cytosol.

When activated by the binding of Ca2+, calmodulin relays the Ca2+ signal onward by undergoing a conformational change and then:

binding to Ca2+-calmodulin-dependent protein kinases (CaM-kinases), which then phosphorylate other intracellular proteins.

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase (RTK) called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization?

a mutation that prevents RGFR from binding to RGF

what pathway is activated most by RTKs

• The phosopholipase C/inositol phospholipid signaling pathway

• The Ras signaling pathway

• MAP-kinase signaling module
  

Ras is activated by a Ras-activating protein that:

causes Ras to exchange GDP for GTP.

what does PI 3-kinase phosphorylate

a lipid in the plasma membrane

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to

create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane

In the Notch signaling pathway, the tail of the cell surface receptor travels to the nucleus where it regulates the transcription of specific genes.

True

Parallel intracellular signaling pathways can interact, in part, because the protein kinases in one pathway can phosphorylate and thereby regulate proteins in other pathways.

True

What occurs in interphase

• cell grows in size

• DNA is replicated

• genes are transcribed

In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated?

at the end of G2

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only?

The cells produced would get smaller and smaller.

Cell cycle characteristics

• An unfavorable environment can cause cells to arrest in G1.

• A cell has more DNA during G2 than it did in G1.

• The rapid divisions that occur in an early embryo have short G1 and G2 phases.

Which of the following is good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution?

• A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle.

• The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans.

• The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast.
  

Progression through the cell cycle requires a cyclin to bind to a Cdk because

the binding of a cyclin to Cdk is required for Cdk enzymatic activity.

Levels of Cdk activity change during the cell cycle, in part because

cyclin levels change during the cycle.

he concentration of mitotic cyclin (M cyclin)

falls toward the end of M phase as a result of ubiquitylation and degradation.

Mitogens

extracellular signals that stimulate cell division.

The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by

inhibiting cyclin transcription.

The G1 DNA damage checkpoint

involves the inhibition of cyclin–Cdk complexes by p21

Cells in the G0 state

do not divide.

Irradiated mammalian cells, that is cells subjected to large amounts of radiation, usually stop dividing and arrest at a G1 checkpoint. The following events, A-D, are involved for a cell to arrest at the G1 checkpoint.

A. production of p21
B. DNA damage
C. inhibition of cyclin–Cdk complexes

D. accumulation and activation of p53

What is the correct order of occurrence for these events?

DNA damage, p53, p21 production, inhibition of cyclin-Cdk complexes

DNA synthesis occurs where

origins of replication

what does the phosphorylation and degredation of Cdc6 help ensure

DNA is replicated only once in each cell cycle

DNA synthesis can only begin after

prereplicative complexes assemble on the ORCs

How does S–Cdk help guarantee that replication occurs only once during each cell cycle?

It phosphorylates the Cdc6 protein, marking it for destruction.

If DNA is damaged or incompletely replicated in S phase, what molecule’s inhibition prevents the cell from entering M phase?

Cdc25

how does mitotic Cdk become active

it must be phosphorylated by an activating kinase

what makes the Cdk inactive even if it has been phosphorylated by the activating kinase

Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1)

Active M-Cdk phosphorylates the activating phosphatase (Cdc25) to create a

positive feedback loop

Condensins

assemble into complexes on the DNA when phosphorylated by M-Cdk.

At the end of DNA replication, the sister chromatids are held together by the

cohesins

what do the mitotic spindles help to do

segregation of the chromosomes to the two daughter cells

The principal microtubule-organizing center in animal cells is the

centrosome

A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to

disassemble its nuclear lamina at prometaphase.

what is cytokinesis in plant cells mediated by

microtubule cytoskeleton

Small membrane vesicles derived from the Golgi apparatus deliver what

new cell-wall material for the new wall of the dividing cell.

the phragmoplast forms from the remains of what

interpolar microtubules of the mitotic spindle.

Programmed cell death occurs

by activation of an intracellular death program.

Apoptosis differs from necrosis in that necrosis

causes cells to swell and burst, whereas apoptotic cells shrink and condense.

characteristic of apoptosis

promoted by the release of cytochrome c into the cytosol from mitochondria

Which of the following statements describes how mitogens operate?

They overcome the intracellular braking mechanisms that tend to block progression through the cell cycle.

Which of the following statements describe how growth factors stimulate animal cell enlargement?

They stimulate intracellular protein synthesis.