Chapter 18 - Regulation of Gene Expression

Question 1

regulation of chromatin structure

Answer 1

• structural organization helps regulate expression
• highly packed heterochromatin (condensed DNA) are usually not expressed
• chemical modifications to histones/DNA influence structure/gene expression

Question 2

histone modifications

Answer 2

acetyl groups are attached to positively charged lysines in histone tails (loosen chromatin structure, initiate transcription)

• addition of methyl groups (methylation) can condense chromatin
• addition of phosphate groups (phosphorylation) can loosen chromatin

Question 3

DNA methylation

Answer 3

addition of methyl groups to DNA base, can cause long-term inactivation of genes in cellular differentiation
-genomic imprinting, methylation regulates expression

Question 4

epigenetic inheritence

Answer 4

chromatin modifications do not alter the DNA sequence they may pass to future generations of cells

Question 5

regulation of transcription initiation

Answer 5

chromatin-modifying enzymes provide initial control of gene expression
-make DNA more/less able to bind transcription machinery

Question 6

organization of eukaryotic gene

Answer 6

multiple control elements, segments of noncoding DNA (transcription factor binding sites)
-critical to precise regulation of gene expression

Question 7

enhancers

Answer 7

distal control elements, far away from gene or located on intron

Question 8

activators

Answer 8

protein that binds to an enhancer and stimulates transcription

• one domain binds to DNA, other activates transcription
• facilitate protein-protein interactions resulting in transcription

Question 9

repressors

Answer 9

inhibit expression

-activators and repressors act indirectly, influencing chromatin structure

Question 10

action of enhancers and transcription activators (3 steps)

Answer 10

1. activator proteins bind to enhancer in DNA (3 binding sites)
2. DNA-bending protein brings activators close to promoter
3. activators bind to proteins forming active transcription initiation complex on the promoter

Question 11

coordinately controlled genes

Answer 11

co-expressed eukaryotic genes gave own promoter and control elements

• can be scattered over different chromosomes
• activators recognize specific control elements and promote simultaneous transcription

Question 12

post-transcriptional regulation

Answer 12

mechanisms can operate at various stages, fine tune gene expression rapidly in response to environmental changes

Question 13

RNA processing

Answer 13

alternative RNA splicing, different mRNA molecules are produced from same primary transcript

Question 14

initiation of translation

Answer 14

can be blocked by regulatory proteins that bind sequences/structures of mRNA
-translation of all mRNAs may be regulated simultaneously

Question 15

mRNA degradation

Answer 15

life span of mRNA molecules in cytoplasm is key to determining protein synthesis

• eukaryotic mRNA is more long-lived than prokaryotic
• nucleotide sequences that influence lifespan reside in 3’ UTR

Question 16

protein processing

Answer 16

cleavage and addition of chemical groups are controlled

• selective degradation regulates protein functions length of time
• cells mark proteins for degradation by attaching regulatory protein UBIQUITIN to them recognized by PROTESOMES (large pr- complexes that degrade ub-tagged pr-)

Question 17

noncoding RNA

Answer 17

noncoding DNA consists of genes for RNA (rRNA/tRNA)

-regulate gene expression at two points: mRNA translation and chromatin configuration

Question 18

microRNAs

Answer 18

small single stranded RNA molecules that bind to mRNA and degrade/block translation (half of human genes are regulated by miRNAs)

Question 19

RNA interface

Answer 19

inhibition of gene expression by RNA molecules, mediated by small RNAs (siRNAs are formed from different RNA precursors)
-disables genes for investigating function of the gene (in a lab)