Lecture 18: Cell Expression

Question 1

cell memory via positive feedback loops

Answer 1

transcription factors acts on target genes & can go back to its own promoter to turn itself back on

Question 2

cell memory via histone modifications

Answer 2

histone modification patterns can be passed on to daughter cells by the action of histone modifying enzymes

Question 3

cell memory via DNA methylation

Answer 3

DNA methylation patterns can be passed on to daughter cells by the action of maintenance methyltransferase (enzyme)

Question 4

epigenetic inheritance

Answer 4

patterns of gene expression are
transmitted from parent to daughter cells without altering the
actual nucleotide sequence of the DNA

Both histone modification and DNA methylation affect
chromatin structure and patterns of gene expression without
changing the nucleotide sequence

Question 5

dosage compensation

Answer 5

A mechanism to equalize the amount of X chromosome gene expression for males
and females (i.e. XX and XY individuals have equal levels of expression of X-linked
genes)

Dosage compensation in mammals is via random inactivation of one of the X
chromosomes in females. (Females are mosaics)

X inactivation is irreversible and via an epigenetic mechanism.

Question 6

out of ~21,000 protein-coding genes…

Answer 6

> 7,000 are devoted to cell signaling

Question 7

general idea of cell signaling

Answer 7

an extracellular signaling moelcule (ligand) is able to enter a cell with an intracelullar receptor (can relay, amplify, integrate, distribute) which causes the ligand to undergo a conformational change which forms an effector molecule (which may later gene expression, metabolism, cytoskeleton), which can cause a variety of responses in the cell: division, growth, survival, migration, secretion, contraction, differentiation

Question 8

signal transduction

Answer 8

the process of translating an extracellular signal into intracellulaar effectors that alters cell behavior = signal transduction

Question 9

endocrine signaling

Answer 9

long-range

example: insulin - regulates glucose uptake in cells all over the body

Question 10

paracrine signaling

Answer 10

short-range

autocrine: signal moves itself through signaling cell w/ receptor

example: shh in the limb bud - digit formation

Question 11

morphogen

Answer 11

class of signaling paracrine molecules that diffuse and form a gradient

Question 12

synaptic signaling

Answer 12

both long + short range

The axon of a neuron can be far
away from the neuronal cell body.

The axon terminates at specialized
junctions called synapses.

Once activated, the neuron sends
electrical impulses along the axon,
leading to the release of
neurotransmitters (signals) at the
nerve terminal.

Question 13

contact-dependent signaling

Answer 13

short range

receptor and signal must be in contact w/ their respective cells

example: Delta/Notch

Question 14

Delta/Notch: example of contact dependent signaling

Answer 14

Cell-cell signaling mediated by membrane bound ligand (Delta) and membrane bound receptor (Notch)

Delta/Notch can mediate either inductive signaling or lateral inhibition

Question 15

the same signal can induce diff. responses in —- target cells

Answer 15

different target cells

information conveyed by the signal dependso n how the target cells receives and interorets the signal (developmental history + current state)

Question 16

signals can act rapidly or slowly

Answer 16

speed is determined by effect they produce in the cell

fast -> effect alters protein function (i.e. conf. change//phosphorylation) doesn’t turn on genes

slow -> modifications have to go through gene expression

Question 17

receptors can be intracellular or cell-surface

Answer 17

intracellular receptors receive small hydrophobic signal molecules

Question 18

steroid hormones regulate transcription

Answer 18

steroid hormone (cortisol) enters the plasma membrqane, conformational change activates receptor protein; NLS is exposed + translocated to nucleus, turn on specific target genes

-each hormone binds a different receptor

-each receptor acts at different sites in DNA

-a given hormone usually regulates (Activate or repress) different sets of genes in different cell types

Question 19

cell surface receptors relay extracellular signals via intracellular signaling

Answer 19

1. signal enters plasma membrane w/ receptor protein
2. relay adaptors (?)
3. protein/signal undergo conf. change/autohposphorylates
4. enzymes (kinases, phosphatases, GTP-binding proteins) transduce and amplify
5. small intracellular messenger molecules (Secondary messengers) bind to target genes at cellular level
6. feedback + integrate (?)
7. distribute to effectors
8. generate response

Question 20

key intracellular signaling proteins act as molecular switches

Answer 20

1. signaling by protein phosphorylatin
2. signaling by GTP-binding proteins

Question 21

feedback regulation types

Answer 21

signaling pathway 1: positive feedback -> all-or-none response

signaling pathway 2: negative feedback -> responses that oscillate on and off; shuts down signaling pathway (i.e. contraction of the heart)

Question 22

integration of signals

Answer 22

certain cellular responses require multiple signals