Chapter 18.2 - Eukaryotic Gene Expression

Question 1

Regulation of gene expression (4)

Answer 1

1. Similar to prokaryotes, eukaryotic cells must regulate the expression of their genes
2. Turn genes on or off in response to environmental or developmental signals
3. Essential for cell specialization in multicellular organisms
4. Can be “up-regulated” or “down-regulated”

Question 2

Chromatin structure can affect transcription (2)

Answer 2

1. Histone proteins bind to DNA via positively charged amino acids (chromatin)
2. DNA wound around histones (nucleosomes)

Question 3

Heterochromatin

Answer 3

Regions of chromatin that are packed tightly. Genes are not expressed

Question 4

Euchromatin

Answer 4

Regions of chromatin that are less compacted. Genes are expressed here.

Question 5

Two ways that chromatin structure can affect transcription (Epigenetic Modifications)

Answer 5

1. Chemical modification of histone proteins

2. DNA methylation

Question 6

Chemical modification of histones (2)

Answer 6

1. Acetylation

2. Methylation

Question 7

Acetylation (3)

Answer 7

1. Acetyl Groups are attached to positively charged lysines in histone tails
2. Loosens chromatin structure
3. Promotes transcription

Question 8

Methylation (5)

Answer 8

1. Methyl groups added to histones
2. Causes chromatin to pack tightly (dynamic)
3. Decreases transcription of genes
4. Methyl Groups added to certain bases in DNA
5. Catalyzed by enzyme DNA methyltransferase

Question 9

DNA methylation Reduces Transcription (2)

Answer 9

1. Inhibits binding to transcription factors

2. Recruits specific methyl-bonding proteins that induce formation of heterochromatin

Question 10

DNA Methylation can Silence genes (2)

Answer 10

1. Can cause long term inactivation of specific genes (gene silencing)
2. In female mammals, one of the two copies of the X chromosome is heavily methylated

Question 11

Can modifications be inherited?

Answer 11

Yes, methylation patterns can be transmitted to daughter cells during DNA replication

Question 12

Epigengic Inheritance (3)

Answer 12

1. Chromatin modifications do not alter DNA sequence
2. But can be passed to future generations of cells
3. Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence

Question 13

Control Elements (3)

Answer 13

1. Segments of noncoding DNA that serve as binding sites for transcription factors that help regulate transcription
2. Control elements and transcription factors that bind are critical to the precise regulation of gene expression in different cell types
3. There are two types

Question 14

Two types of control elements

Answer 14

1. Proximal Control Elements

2. Distal Control Elements

Question 15

Proximal Control Elements

Answer 15

Close to the promoter

Question 16

Distal Control Elements

Answer 16

Enhancers - May be far away from a gene or in an intron

Question 17

Eukaryotic Transcription Factors

Answer 17

Proteins that bind to a control element.

1) activators: stimulate transcription
2) repressors: reduce transcription

Question 18

Mechanisms of Post-Transcriptional Regulation (3)

Answer 18

1. Transcription alone does not control gene expression
2. Regulatory mechanisms can operate at various stages after transcription
3. Allow a cell to fine-tune gene expression rapidly in response to environmental changes