Control of Gene Expression

Question 1

how can two cell types with the same DNA be so different

Answer 1

each cell has different levels of gene expression (amt of mRNA made), which will encode for different proteins

Question 2

what do lymphocytes make; red blood cells?

Answer 2

antibodies; hemoglobin

Question 3

what are the ways that gene expression can be controlled

Answer 3

• when and how often gene is transcribed
• how mRNA gene is spliced or processed
• which mRNAs leave nucleus
• which mRNAs are degraded
• which mRNAs are selected for translation by ribosomes
• activation or inactivation of proteins once they’re made

Question 4

briefly describe transcription control

Answer 4

• promoter region has sequences recognized by RNA polymerase and binds to initiate transcription
• regulatory DNA sequences bind to regulatory proteins
• reg. proteins switch transcription of genes on or off

Question 5

what types of interactions can occur between regulatory protein and DNA

Answer 5

through hydrogen bonds, ionic bonds, or hydrophobic interaction

Question 6

how is the expression of genes in bacteria largely controlled

Answer 6

by food availability in the environment

Question 7

describe gene expression in bacteria

Answer 7

• scarce food proteins leads to production of enzymes involved in tryptophan production
• the enzyme gene transcription is controlled by promoter and regulatory sequence called operator
• operator binds to repressor protein to turn genes off OR
• when operator has no repressor bound, gene expression turns on and a single mRNA molecule codes for all 5 enzymes involved in tryptophan synthesis

Question 8

define operon

Answer 8

set of genes that are transcribed into a single mRNA molecule

Question 9

when does a repressor stop the transcription of these tryptophan-producing enzyme genes

Answer 9

when a high level of tryptophan is present

Question 10

how does transcription of lactose degredation occur

Answer 10

• low glucose triggers increase in cAMP
• cAMP binds to CAP activator
• activator interacts and assists polymerase
• increase in transcription of lactose degrading enzyme genes

Question 11

describe eukaryotic transcription

Answer 11

• transcription factors assemble on all promoters bound by RNA polymerase II
• binding of TFIID trans. factor to DNA composed of nucleotides T and A (TATA box)
• binding distorts DNA assisting TFIIB and TFIIA to bind
• TFIIF, TFIIE, TFIIH proteins bind with RNA polymerase II
• TFIIH adds phosphate groups to RNA polymerase II which releases it from other factors to initiate transcription

Question 12

what is chromatin remodeling

Answer 12

• histone acetylase enzymes are added to site of transcription by activator proteins
• adds acetyl group to histones that relaxes DNA interaction
• activator proteins recruits chromatin remodeling complexes which relaxes chromatin
• allows for greater accessibility of transcription factors and RNA polymerase to sight of expression

Question 13

how can regulatory proteins affect eukaryotic transcription

Answer 13

by activating or repressing

Question 14

how can cells change expression of certain genes; give an example

Answer 14

thru external stimuli

• starvation leads to low glucose
• glucocorticoids produced
• tryosine aminotransferase is made (amt made is controlled by expression of its associating gene)
• tryosine to glucose conversion

Question 15

external signals can induce expression of ________ gene(s)

Answer 15

many

Question 16

what is the glucocorticoid receptor

Answer 16

regulatory protein that binds DNA when bound to glucocorticoid hormone

Question 17

what are the differences between eukaryotic and bacterial gene expression

Answer 17

• types of RNA polymerase
• need/lack of trancription factor proteins
• activating/repressing regulatory proteins location
• compact chromatin structure consideration (eukaryotic only)