Exam 4 - Chapter 18

Question 1

gene expression

Answer 1

• nearly all somatic cells contain an individuals entire genome
• differences in gene expression result in different types of cells with different structions and fucntion

Question 2

gene regulation in prokaryotes

Answer 2

-control mostly at the transcription level

operon = promoter + operator = genes

Question 3

repressor

Answer 3

produced in the cell, binds to operator and prevents transcription by blocking RNA polymerase

Question 4

activator

Answer 4

produced in the cell, binds to promoter and increases transcription

Question 5

inducer

Answer 5

may be produced by the cell or available in the environment, can activate or repress transcription

Question 6

Negative gene regulation

Answer 6

operons switched off by active form of repressor

Question 7

Repressible operon

Answer 7

usually on, binding of repressor to operator shuts off transcription

Question 8

trp operon

Answer 8

controls the synthesis of the amino acid tryptophan

Question 9

trp reporessor

Answer 9

only active in the presense of its corepressor tryptophan

Question 10

inductible operon

Answer 10

usually off, an inducer inactivates the repressor and turns on transcription, example is the lac operon

Question 11

positive gene regulation

Answer 11

regulatory protein binds to control region and turns on transcription

Question 12

eukaryotic gene regulation - access to genes

Answer 12

• dna loosely wraps around histone proteins to form chromatin
• histone package and order dna into units within chromatin called nucleosomes
• regions of chromatin can be condensed into heterchromatin
• epigenetic modifications are when gene expression is altered by the dna itself is not

Question 13

Histone modifications

Answer 13

• acetyl groups loosen chromatin
• phosphate groups (-) loosen chromatin
• methyl groups condense chromatin

Question 14

DNA methylation

Answer 14

• addition of methyl groups (condenses DNA) reduces transcription
• can cause long-term gene inactivation/silencing

Question 15

eukaryotic gene regulation - transcriptional controls

Answer 15

• transcription factors bind to the promoter to bring in RNA ploymerase
• control elements regulate transcription
• transcription factors and activators bind increasing transcription through enhancers
• repressors can bind to promoter or enhancer for a gene to block transcription

Question 16

eukaryotic gene regulation - post transcriptional mRNA modifications

Answer 16

• alternate RNA splicing where different mRNA transcripts are produced from the starting DNA
• mRNA degradation is that each mRNA has a defined lifespan and decays at a specific rate
• RNA interface (RNAi) are when molecules inhibit gene expression
• Small interfering RNA (siRNA) and microRNA (miRNA) centgral to RNAi

Question 17

eukaryotic gene regulation - translational controls

Answer 17

-initiation factors are required for formation of the translation initiation complex
-Regulatory proteins can bind to mRNA and block the translational machinery from assembling
-Translation of all mRNAs in a cell may be regulated by
increasing/decreasing the amount of initiation factors that would increase/decrease all translation

Question 18

eukaryotic gene regulation - Post-Translation Protein Modification & Degradation

Answer 18

-Proteins can be chemically modified by the addition of methyl,
phosphate, acetyl, and ubiquitin groups
-The addition or removal of these groups can regulate protein activity,location in the cell, or lifespan
-Modifications occur in response to stimuli like stress, lack of nutrients, heat, or UV light