Topic 7.2: Transcription and Gene Expression

Question 1

Gene

Answer 1

Sequence of DNA which is transcribed into RNA

Question 2

Sections of a Gene

Answer 2

1) Promoter (transcription initiation site)
2) Coding sequence (the region transcribed)
3) Terminator (transcription termination site)

Question 3

DNA Double strand and transcription

Answer 3

1) The antisense strand is transcribed into RNA (complementary)
2) The sense strand is not transcribed into RNA
(identical)

Question 4

Transcription

Answer 4

Process by which a DNA sequence is copied into a complementary RNA sequence by RNA polymerase

Question 5

Steps in transcription

Answer 5

1) Initiation
2) Elongation
3) Termination

Question 6

Initiation

Answer 6

1) RNA polymerase binds to a promoter and unwinds DNA
2) It breaks the H bonds between complementary bases
3) Nucleoside triphosphates bind to complementary bases

Question 7

Elongation

Answer 7

1) RNA polymerase covalently joins the nucleotides together. The two extra phosphates are released (provides energy)
2) Transcription occurs in a 5’ → 3’ direction (antisense strand)

Question 8

Termination

Answer 8

At the terminator site, RNA polymerase is detached and the RNA sequence is released (and the DNA rewinds).

Question 9

Modifications of mRNA after transcription in eukaryotic cells (3)

Answer 9

1) Capping
2) Polyadenylation
3) Splicing

Question 10

Capping

Answer 10

1) Addition of a methyl group to the 5’-end of the transcribed RNA
2) The methylated cap provides protection against degradation by exonucleases
3) Allows the transcript to be recognized by the cell’s translational machinery

Question 11

Polyadenylation

Answer 11

1) Addition of a long chain of adenine nucleotides (a poly-A tail) to the 3’-end of the transcript
2) The poly-A tail improves the stability of the RNA transcript and facilitates its export from the nucleus

Question 12

Splicing

Answer 12

Non-coding regions within genes are removed

Question 13

Introns

Answer 13

Non-coding regions in genes

Question 14

Exons

Answer 14

Coding regions of genes

Question 15

Alternative Splicing

Answer 15

Exons can be selectively removed to form different proteins from the same gene

Question 16

Regulators of transcription activity

Answer 16

1) Transcription factors

2) Regulatory proteins

Question 17

Transcription factors

Answer 17

Form a complex with RNA polymerase at the promoter

Without these factors RNA Pol cannot initiate transcription

Question 18

Regulatory proteins

Answer 18

Bind to DNA sequences outside of the promoter and interact with the transcription factors

Question 19

Activator proteins

Answer 19

Bind to enhancer sites and increase the rate of transcription

Question 20

Repressor proteins

Answer 20

Bind to silencer sequences and decrease the rate of transcription

Question 21

The environment of a cell has an impact on gene expression

Answer 21

Chemical signals within the cell can trigger changes in levels of regulatory proteins or transcription factors in response to stimuli

Question 22

Examples of organisms changing their gene expression patterns in response to environmental changes

Answer 22

1) Hydrangeas change colour depending on the pH of the soil
2) The Himalayan rabbit produces a different fur pigment depending on the temperature
3) Humans produce different amounts of melanin depending on light exposure

Question 23

Nucleosomes and Transcription Regulation in Eukaryotes

Answer 23

Histones proteins have protruding tails that determine how tightly the DNA is packaged within nucleosomes

Question 24

Acetylation and DNA package

Answer 24

Makes DNA less tightly packed

Question 25

Methylation and DNA package

Answer 25

Makes DNA more tightly packed

Question 26

Types of Chromatin

Answer 26

1) Heterochromatin (Supercoiled | No transcription)

2) Euchromatin (Loosely packed | Transcription)

Question 27

DNA Methylation

Answer 27

1) Increased methylation of DNA decreases gene expression
2) Genes that are not transcribed tend to exhibit more DNA methylation than genes that are actively transcribed
3) Environmental factors (e.g. diet, pathogen exposure, etc.) influences DNA methylation.