Introduction To Genetics

Question 1

What is molecular genetics?

Answer 1

• Expression and regulation of genes at a molecular level.
• investigative approach that involves the application of laboratory methods and research strategies.
• Sub discipline of genetics. Genes are units of heredity. Molecular genetics is concerned with the physical and chemical properties.
• Understands the nature of inherited characteristics at a molecular level in terms of DNA + RNA structure end sequence and factors that influence gene expression.
• The branch of genetics that deals with hereditary transmission and variation on the molecular level.

Question 2

Advances in molecular genetics:

Answer 2

• Forensics
• Genetic testing for disease
• Identification of horse meat in British food.
• Ancestral DNA lineage

Question 3

Flow of Genetic Information

Prokaryotes

Answer 3

DNA - mRNA - Protein

Through transcription and translation.

Question 4

Flow of Genetic Information

Eukaryotes

Answer 4

DNA
Pre-mRNA
mRNA
Protein

Question 5

What is transcription?

Answer 5

Copies one of the DNA strands by making a complimentary RNA strand.

5’ to 3’ sequence - based on location of carbon atoms.

Does not require a primer.

Question 6

What enzyme is involved with transcription?

Answer 6

RNA Polymerases

Question 7

What does mRNA code for?

Answer 7

Codes for protein and other RNA’s.

Question 8

What is rRNA?

Answer 8

Part of ribosome

Question 9

What is tRNA?

Answer 9

Carries amino acids to the ribosome.

Question 10

What is the level of gene product controlled by?

Answer 10

Transcription regulation

Question 11

Where does transcription take place?

Eukaryotes

Answer 11

In the nucleus

Question 12

What happens with transcription in eukaryotes?

Answer 12

After transcription the RNA product travels to its next destination.

mRNA goes to the cytosol where ribosomes translate it.

Question 13

Where does transcription take place?

Prokaryotes

Answer 13

No nuclear membrane.

mRNA can be translated as soon as made.

Question 14

What are RNA polymerases?

Answer 14

Enzymes that catalyse the formation of phosphodeister bonds between ribonucleotides.

Form polymers of RNA by copying a DNA template.

Question 15

Prokaryotic RNA polymerase

What is it made up of?

Answer 15

5 different core subunits and a sigma factor.

β+ and β = 2 large sub units

α = 2 small subunits

ω = 1 small subunit (smallest)

1 sigma factor (various)

Each subunit is a polypeptide chain of amino acids

Question 16

How is transcription regulated?

Answer 16

Not all genes are expressed all the time.

They can be switch on / off depending on the conditions.

E.g. in response to nutrients, temp or during development. Or to confer specific properties on a cell within a tissue or organ.

Question 17

What do sigma factors do?

Answer 17

Allow the prokaryotic polymerase to recognise and bind different promoter sequences.

O70 - most prokaryotic promotors
054 - nitrogen-regulates promoters
032 - heat shock regulation promoters

Question 18

How do species differ with sigma factors?

Answer 18

Have different number of sigma factors.

Typically more sigma factors improves response to changing conditions.

Question 19

What is the promoter recognition by the bacterial RNA polymerase holoenzyme?

Answer 19

Core RNA polymerase associates with a sigma factor that binds to a specific promoter sequence (green) in the DNA.

Contacting sequences centered at -10 and -35 region.

The α terminal domains contact the up element (orange), which is located upstream of the -35 region on some promoters.

Question 20

The tighter the bind to the sequence in transcription equals

Answer 20

The higher level of transcription

Question 21

Key features of prokaryotic transcription

Answer 21

• only 1 RNA polymerase
• sigma factor
• transcription and translation are coupled
• genes contain NO introns
• transcripts can be polycistronic

Question 22

Key features of eukaryotic transcription?

Answer 22

• 3 RNA polymerases Pol I, Pol II, Pol III
• No sigma factor
• Transcription and translation are NOT coupled
• Genes frequently contain introns
• Transcripts are monocistronic

Question 23

Steps of transcription

Answer 23

1) initiation
2) elongation
3) termination

Question 24

Transcription

1) initiation

Answer 24

The most important and complex

Question 25

Transcription steps

2) Elongation

Answer 25

RNA polymerase continues to add nucleotides to the growing chain.

Question 26

Transcription steps

3) Termination

Answer 26

RNA polymerase reaches the end of the gene and reads a signal to stop transcribing.

Question 27

Where does transcription start?

Answer 27

RNA polymerase initiates transcription at specific sites near the start of the gene.

These sequences are called promoters.

Question 28

What are the two transcription sequence promoters?

Answer 28

Prokaryotic promoters

Eukaryotic promoters

Question 29

There are two important prokaryotic promoter elements for RNAP binding

Answer 29

• 35 region e.g. TTGACAT
• 10 region e.g. TATAAT

Known as consensus sequences

Question 30

What is a consensus sequence?

Answer 30

A sequence of nucleotides found in different genes which are similar or identical.

Companion of several similar sequences leads to an “average” sequence.

E.g.

TATGAT - sequence 1
TATAAT - sequence 2
TAATAT - sequence 3
TATATT - sequence 4

TATAAT - consensus sequence

Question 31

Stages of initiation

Answer 31

1) RNA polymerase holoenzyme bunds to the promoter region, forming the closed complex.
2) The enzyme then separates the template and non-template strand, forming the open complex.
3) Synthesis of an RNA strand is initiated, using base-pairing interactions with the template strands.
4) RNA polymerase frequently synthesises only a few base pairs at first and then releases the product, which is known as abortive initiation.
5) When an RNA product of around 9-11 nucleotides is successfully synthesised, RNA polymerase undergoes a conformational change and loosens it’s grip on the stigma subunit to become an elongating comped that continues to synthesise RNA as it translocates along the DNA template.

Question 32

Prokaryotic Transcription Initiation

Summarised

Answer 32

• RNA polymerase walks on the DNA
• RNA polymerase (sigma factor) binds to promoter.
• DNA strands separate and one strand is copied.
• Sigma factor dissociates after 10 nucleotides have been added.
• Core RNA polymerase continues to end.

Question 33

Termination bacteria

Two mechanisms

Answer 33

Rho-dependent and rho-independent

Rho = protein

Bacteria is typically rho-independent