Gene mutation and expression

Question 1

What is a mutation?

Answer 1

Change in DNA base sequence

Question 2

How can mutations occur?

Answer 2

Spontaneously if DNA misread during replication

UV or ionising radiation, chemicals and viruses can increase rate of mutations

Question 3

What are the 3 types of gene mutations?

Answer 3

Substitution = 1 base replaced by another
Deletion = 1 base removed from sequence
Insertion = 1 base added into sequence

Question 4

What do mutations change?

Answer 4

Amino acid sequence coded for by gene leading to different polypeptide and potentially a different tertiary structure

Question 5

What is a substitution mutation?

Answer 5

Although triplet code has changed amino acid sequence of a protein doesn’t

due to the degenerate nature of the genetic code

Question 6

What are deletion mutations?

Answer 6

Causes frameshift where entire sequence after deletion shifts to left by 1 base so all triplets after deletion are changed

more likely to change amino acid sequence because they cause a frameshift

Question 7

What are insertion mutations?

Answer 7

Causes frameshift where entire sequence after insertion shifts to right by 1 base so all triplets after deletion are changed

more likely to change amino acid sequence because they cause a frameshift

Question 8

What are transcription factors?

Answer 8

Proteins that bind to specific DNA sequences to initiate transcription of genes into mRNA

Question 9

What are transcription factors role in gene expression in eukaryotes?

Answer 9

mRNA produced during transcription carries genetic code from DNA to ribosomes, allowing production of proteins

Question 10

What happens when a gene is switched off in eukaryotes?

Answer 10

Transcription factors can’t bind to DNA preventing transcription process and so synthesis of polypeptides

Question 11

What is epigenetic regulation in eukaryotes?

Answer 11

Involves changes in gene expression without altering the underlying DNA sequence

Question 12

What is an example of epigenetic modification in eukaryotes?

Answer 12

Histone modifications can influence chromatin structure and gene activity by making DNA more or less accessible for transcription

Question 13

What are examples of modifications promoting transcription in eukaryotes?

Answer 13

Acetylation = involves adding acetyl groups to histones, decreasing their positive charge resulting in looser DNA coil increasing transcription

Phosphorylation = adding phosphate groups to histones reducing their positive charge resulting in looser DNA coil and increased transcription

Question 14

What’s an example of a modification inhibiting transcription in eukaryotes?

Answer 14

Methylation = involves adding methyl groups to histones increasing hydrophobic interactions tightening coiling of DNA reducing transcription

Question 15

How does chromatin remodelling affect gene expression in eukaryotes?

Answer 15

Negatively charged DNA wraps around positively charged histone proteins to form chromatin

Question 16

What are the 2 forms chromatin can exist in eukaryotes?

Answer 16

Heterochromatin = densely packed form of chromatin making it difficult for RNA polymerase to access genes preventing transcription

Euchromatin = loosely packed form of chromatin allowing easy access for RNA polymerase enabling active transcription of genes

Question 17

What is chromatin remodelling essential for in eukaryotes?

Answer 17

Controlling when and where genes are expressed ensuring proteins produced only when needed allowing cells to control which genes are active, influence cell function, and respond to environmental signals

Question 18

What is an operon?

Answer 18

Gene cluster controlled by single promoter allowing coordinated expression

Question 19

What are the key components of an operon?

Answer 19

Regulatory genes = encode proteins regulating expression of structural genes
Promoter region = site where RNA polymerase binds to initiate transcription
Structural genes = code for proteins typically enzymes
Operator region = sequence where regulatory proteins (e.g repressor) can bind

Question 20

What is a lac operon?

Answer 20

Group of genes in bacterium Escherichia coli that control lactose metabolism allowing them to use lactose as an energy source when glucose is scarce

Question 21

What is the function of the lac regulatory gene?

Answer 21

Codes for repressor protein that can inhibit and control lac operon’s activity

Question 22

What are the 3 genes essential for lactose metabolism?

Answer 22

• lacZ
• lacY
• lacA

Question 23

What enzyme does lacZ produce and what’s its function?

Answer 23

β-galactosidase

breaks down lactose into glucose and galactose

Question 24

What enzyme does lacY produce and what’s its function?

Answer 24

Lactose permease

transports lactose into the cell

Question 25

What enzyme does lacA produce and what's its function?

Answer 25

Transacetylase modifies lactose or its by-products

Question 26

How does the lac operon conserve energy?

Answer 26

Producing lactose-metabolising enzymes only when lactose is present

Question 27

What happens at the lac operon when lactose isn't present?

Answer 27

1) repressor protein binds to operator region 2) RNA polymerase blocked from promoter region 3) RNA polymerase can't transcribe structural genes 4) enzymes for lactose metabolism aren't produced

Question 28

What happens at the lac operon when lactose is present?

Answer 28

1) lactose binds to repressor protein 2) repressor protein changes shape and is released from operator region 3) RNA polymerase can bind to promoter region initiating transcription 4) RNA polymerase transcribes structural genes leading to production of enzymes necessary for lactose metabolism

Question 29

Hoe does presence of glucose impact lac operon activity?

Answer 29

Indirectly inhibits lac operon via a signalling molecule cyclic AMP

Question 30

How is lac operon activity controlled when only lactose is present?

Answer 30

1) cAMP levels increase and cAMP binds to cAMP receptor protein (CRP) 2) CRP-cAMP complex up-regulates transcription of lac operon 3) lactose metabolism is optimised

Question 31

How is lac operon activity controlled when lactose and glucose is present?

Answer 31

1) glucose reduces cAMP levels 2) CRP-cAMP complex cannot form 3) lac operon's transcription is down-regulated 4) lactose metabolism enzymes aren't produced