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Cell Biology > Lecture 9 Slides > Flashcards

Lecture 9 Slides Flashcards

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0
Q

Regulatory genes

A

Turn genes on and off

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1
Q

What are housekeeping genes

A

Constitutive genes - expressed all the time

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2
Q

Four levels of regulation of gene expression

A
  1. Transcription
  2. Post transcription
  3. Translation
  4. Post translation
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3
Q

Three ways to regulate gene expression post transcription

A

RNA processing, eg splicing
Rna degradation
Rna transport, eg nuclear export

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4
Q

Half life of prokaryotic rna

A

Three minutes

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5
Q

Half life of eukaryotic rna

A

Minutes to hours

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6
Q

What does regulation depend on during translation

A

Whether or not ribosome can translate mRNA

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7
Q

Three ways to regulate gene expression post translation

A

Affect protein stability - some proteins denature easily
Some proteins are targeted for degradation
Modifications eg phosphorylation

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8
Q

Example of negative control in transcription

A

Repressing splicing so intron is not removed

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9
Q

Positive control example during transcription

A

Using an activator to make splicing happen

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10
Q

At what point in ponytail does mRNA start to degrade

A

When there are 25 or fewer adenines

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11
Q

Is mRNA decamped before degradation

A

Yes

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12
Q

In what direction does degradation happen

A

5’ to 3’

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13
Q

What initiation factors initiate translation

A

EIF4G and eIF4E

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14
Q

What enzyme degrades poly A tail

A

Deadenylase

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15
Q

What is a translation repressor protein

A

A protein that blocks the start codon AUG

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16
Q

How can a newly synthesized protein fold?

A
  1. Correctly folded without help
  2. Correctly folded with help of a molecular chaperone
  3. Incompletely folded and digested by the proteasome
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17
Q

What digests a protein that is incompletely folded

A

A proteosome

18
Q

What kind of cells have proteosomes in the cytosol

A

Eukaryotes, archea, and some bacteria

19
Q

What is Ubiquitin ligase

A

An enzyme that binds Ubiquitin

20
Q

Where is Ubiquitin added to unwanted protein

A

To side chain, ends with N terminal. Add c terminal end of Ubiquitin.

21
Q

Polyubiquitin

A

More than one Ubiquitin has been added to unwanted protein

22
Q

What happens to unwanted protein once Ubiquitin has bound to it

A

It goes to a proteosome, where it is unfolded. Ubiquitin doesn’t go in. Amino acids are recycled.

23
Q

How many amino acids in Ubiquitin

A

72

24
Q

How many lysine residues in Ubiquitin

A

Seven

25
Q

What are the two subunits of Ubiquitin ligase? What is their function.

A

E2- Ubiquitin transferase

e3- recognizes target protein

26
Q

What is E1 unit

A

It is the carrier of Ubiquitin

27
Q

What does E1 do with the Ubiquitin it carries

A

It charges E2

28
Q

What do proteosome target proteins have

A

PEST motif, which is phosphorylated

29
Q

Destruction box

A

Amino acid sequence required for degradation

30
Q

n-end rule

A

N-terminal amino acid of a protein determines its half life (likelihood of being degraded)

31
Q

How is Ubiquitin ligase activated

A

Phosphorylation by protein kinase

Allosteric transition by ligand binding or protein subunit addition

32
Q

How is a degradation signal activated

A

Phosphorylation by protein kinase
Unmasking by protein dissociation
Creation of destabilizing N-terminus

33
Q

Density and molecular weight of proteosome

A

26s

2.5 MDa

34
Q

Proteosome subunits

A 
19s cap
20s cylinder (active site)
35
Q

What is active site of proteosome

A

20s cylinder

36
Q

What does unfolding and pulling of protein throufh cylinder require

A

ATP

37
Q

How does target protein attach to proteosome

A

At unfoldase ring

38
Q

Contents of cap of proteosome

A

Ubiquitin receptor
Unfoldase ring
Ubiquitin hydrolase (to release Ubiquitin)

39
Q

Shape of unfoldase ring

A

Hexameric

40
Q

Is inactivation by polyubiquination reversible

A

No

41
Q

Cell life cycle phasesq

A

Interphase - G1, S phase, G2

M phase- mitosis and cytokinesis

42
Q

What is cyclin

A

An enzyme whose concentration varies with stages of cell life cycle

43
Q

When is cyclin concentration high? Low?

A

High in mitosis

Low during interphase

Cell Biology (35 decks)

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