Gene Expression

Question 1

What helps regulate gene expression?

Answer 1

Structural organization of chromatin

Question 2

What are usually not expressed?

Answer 2

Genes with highly packed heterochromatin

Question 3

What is heterochromatin?

Answer 3

• Chromosome material of different density from normal
• Heavier

Question 4

What influences chromatin structure and gene expression?

Answer 4

Chemical modifications to histones and DNA of chromatin

Question 5

What are histone tails?

Answer 5

• Protruding ends of histone proteins that extend from the nucleosome

Question 6

What is acetylation?

Answer 6

The addition of acetyl groups to histone tails

Question 7

Acetylation benefits

Answer 7

Promotes loose chromatin structure that permits transcription

Question 8

What is DNA methylation?

Answer 8

The addition of methyl groups to DNA

Question 9

DNA methylation effects

Answer 9

• Can reduce transcription in some species
• Can cause long-term inactivation of genes
• Regulates expression of either maternal or paternal alleles of certain genes at the start of development

Question 10

Methylation in histone effects

Answer 10

Affects how tightly DNA is packed

Question 11

How does phosphorylation affect chromatin?

Answer 11

Addition of phosphate groups next to a methylated amino acid can loosen chromatin

Question 12

What is epigenetic inheritance

Answer 12

Chromatin modifications do not alter the DNA sequence, they may be passed to future generations of cells

Question 13

What is regulation of transcription initiation?

Answer 13

• Chromatin modifying enzymes provide initial control of gene expression
• Make region of DNA more or less able to bind to transcription machinery

Question 14

What are control elements?

Answer 14

DNA sequences that regulate gene expression by binding transcription factors

Question 15

Where are control elements located?

Answer 15

Near (proximal) or far (distal) from the promoter

Question 16

What is an activator?

Answer 16

A protein that binds to an enhancer and stimulates transcription

Question 17

Distal elements

Answer 17

• located far from the gene they regulate
• can be grouped as “enhancers”
• Can be located in the intron

Question 18

What are the two domains of activators?

Answer 18

1. DNA-Binding Domain
2. Activation Domain

Question 19

DNA-Binding Domain

Answer 19

Binds to specific DNA sequences like enhancers

Question 20

Activation Domain

Answer 20

Activates transcription

Question 21

What is the poly-A signal?

Answer 21

A sequence in the last exon transcribed into RNA that signals where the transcript is cleaved

Question 22

What happens after the poly-A signal is transcribed?

Answer 22

Transcription continues for hundreds of nucleotides beyond the poly-A signal before terminating

Question 23

Transcription Factors - Functions

Answer 23

• Initiates transcription
• Some factors function as repressors, inhibiting expression of gene
• Act indirectly by influencing chromatin structure

Question 24

What is combinatorial control of gene activation?

Answer 24

Transcription is activated only when a specific combination of control elements and appropriate activator proteins are present

Question 25

How are co-expressed eukaryotic genes organized?

Answer 25

Not in operons; each has its own promoter and control elements

Question 26

Where are co-expressed eukaryotic genes located?

Answer 26

They are scattered across different chromosomes but share the same combination of control elements

Question 27

How are co-expressed genes transcribed simultaneously?

Answer 27

Activators recognize shared control elements and promote simultaneous transcription of these genes

Question 28

How can the initiation of translation be blocked?

Answer 28

Regulatory proteins can bind to mRNA sequences or structures, preventing translation

Question 29

Why is mRNA lifespan important?

Answer 29

- It determines how much protein is synthesized - The longer it lasts, the more protein is made

Question 30

How does eukaryotic mRNA lifespan compare to prokaryotic mRNA?

Answer 30

Eukaryotic mRNA is longer-lived than prokaryotic mRNA

Question 31

Where is the lifespan of eukaryotic mRNA determined?

Answer 31

It resides in the 3' UTR of the mRNA

Question 32

What happens to proteins after translation?

Answer 32

Proteins undergo processing such as cleavage or the addition of chemical groups

Question 33

How is the length of time a protein functions regulated?

Answer 33

By selective degradation

Question 34

What does ubiquitin do in protein degradation?

Answer 34

Ubiquitin is a small protein that tags proteins for degradation by proteasomes

Question 35

What do proteasomes do?

Answer 35

They are large protein complexes that recognize ubiquitin-tagged proteins and degrade them

Question 36

Noncoding RNAs (ncRNAs)

Answer 36

- They do not code for proteins but regulate gene expression at mRNA translation and chromatin configuration - Significant amounts of the genome can be transcribed into ncRNAs

Question 37

What are microRNAs (miRNAs)?

Answer 37

- Small single-stranded RNA molecules that bind to mRNA to degrade it or block its translation - Expression of at least half of all human genes can be regulated by miRNAs

Question 38

How do miRNAs interact with mRNA?

Answer 38

1. miRNA binds to mRNA with at least 7 complementary bases 2. If bases are complementary along the whole thing, mRNA is degraded 3. If the match is less complete, translation is blocked

Question 39

What is RNA interference (RNAi)?

Answer 39

- The inhibition of gene expression by RNA molecules - Also used in labs to disable genes and study their functions

Question 40

What controls RNAi?

Answer 40

Small interfering RNAs (siRNAs)

Question 41

What is cell differentiation?

Answer 41

When cells become specialized

Question 42

What is morphogenesis?

Answer 42

Physical process giving an organism its shape

Question 43

Process to transform from zygote to adult

Answer 43

1. Cell division 2. Cell differentiation 3. Morphogenesis