Cellular Control

Question 1

What are the types of gene mutations?

Answer 1

• Insertion
• Deletion
• Substitution

Question 2

Define substitution mutation.

Answer 2

When one or more nucleotides are substituted for another in a base sequence.

Question 3

Define insertion mutation.

Answer 3

Addition of one or more nucleotide base pairs into a DNA sequence.

Question 4

Define deletion mutation.

Answer 4

When one or more nucleotides are deleted in a base sequence.

Question 5

What is a point mutation?

Answer 5

This is where only one nucleotide is affected.

Question 6

What are the consequences of substitution mutation of a single nucleotide?

Answer 6

Changes the codon in which it occurs, if new codon codes for diff. amino acid, may lead to change in primary structure of protein synthesised.

But, degenerate nature of genetic code may mean that new codon codes for same amino acid so no change in protein.

Question 7

What are the consequences of an insertion or deletion mutation?

Answer 7

Leads to frameshift mutation where reading frame of sequence of bases is framed (due to triplet code & non-overlapping). Changes every codon from the point of mutation.

Question 8

When does a frameshift mutation not occur?

Answer 8

When number of nucleotides changed is a multiple of three, because it corresponds to full codons. Protein synthesised will still be affected as new amino acid is added.

Question 9

What are the different effects of mutations?

Answer 9

• No effect: Because normally functioning proteins are still synthesised.
• Damaging: Proteins no longer synthesised or proteins synthesis are non-functional which can interfere with essential processes.
• Beneficial: protein synthesised which is useful characteristic in phenotype.

Question 10

What causes/increases rate of mutations?

Answer 10

Mutations can occur spontaneously, rate increased by mutagens.

Question 11

What is a mutagen?

Answer 11

A physical, biological or chemical agent which causes mutations.

Question 12

What is an example of a physical mutagen?

Answer 12

Ionising radiations such as X-rays, break one or both strands of DNA and mutations can occur in the process.

Question 13

What is an example of a chemical mutagen?

Answer 13

Deaminating agents, chemically alter bases in DNA such as converting cytosine to urasil, changing base sequence.

Question 14

What are examples of biological mutagens?

Answer 14

Alkylating agents, viruses, base analogs.

Question 15

What is a silent mutation?

Answer 15

Change in the sequence of nucleotide bases which constitutes DNA, without subsequent change in the amino acid or the function of the overall protein.

Question 16

What is a missense mutation?

Answer 16

Results in incorporation of an incorrect amino acid into the primary structure when the protein is synthesised.

Question 17

What is a nonsense mutation?

Answer 17

Results in a codon becoming a stop codon instead of coding for an amino acid. Leads to shorter protein being synthesised, usually non-functional. Normally have negative effects on phenotype.

Question 18

What is an intron?

Answer 18

Sections of DNA that do not code for a polypeptide. Contain regulatory sequences (promoter regions, operator regions and terminator regions).

Question 19

What is an exon?

Answer 19

Sections of DNA that code for a polypeptide. Consists of regulatory genes (transcription factors) and structural genes (e.g. enzymes, antibodies, peptide hormones).

Question 20

What is gene expression?

Answer 20

The process by which the genetic code of a gene is used to direct protein synthesis.

Question 21

Why is the control of gene expression necessary?

Answer 21

Each cell contains entire genome, including genes not needed by cell. So expression of genes and rate of synthesis of protein products such as enzymes and hormones must be regulated, only expressed when needed to prevent vital resources being wasted.

Question 22

Why is gene regulation needed?

Answer 22

Required for cells to specialise and work in coordinated way.

Question 23

What are the levels at which genes are regulated?

Answer 23

• Transcriptional
• Post-transcriptional
• Translational
• Post-translational

Question 24

What is the transcriptional level?

Answer 24

Where genes can be turned on or off.

Question 25

What is the post-transcriptional level?

Answer 25

mRNA can be modified which regulates translation and types of proteins produced.

Question 26

What is the translational level?

Answer 26

Translation can be stopped or started.

Question 27

What is the post-translational level?

Answer 27

Proteins can be modified after synthesis which changes their functions.

Question 28

What are housekeeping genes?

Answer 28

Genes that code for enzymes which are necessary for reactions present in metabolic pathways like respiration and are constantly required.

Question 29

What are tissue-specific genes?

Answer 29

Genes which code for protein-based hormones (required for the growth and development of an organism or enzymes) which are only required by certain cells at certain times to carry out short-lived response.

Question 30

What are methods used at transcriptional level of control?

Answer 30

Heterochromatin, histone modification an transcription factors.

Question 31

How does heterochromatin regulate gene expression?

Answer 31

DNA tightly coiled around histone proteins so RNA polymerase cannot access, which prevents gene transcription.

Question 32

How does histone modification regulate gene expression?

Answer 32

- DNA coils around histones, modification increases/decreases degree of packing. - Acetylation or addition of phosphate groups reduce positive charge, DNA coils less tightly (DNA= negatively charged) so some genes can be transcribed. - Addition of methyl groups makes histones more hydrophobic, binds more tightly, thus DNA coils more tightly.

Question 33

How do transcription factors regulate gene expression?

Answer 33

- Controls rate of transcription of genetic info from DNA to mRNA by binding to specific DNA sequence. - Turns genes on and off to ensure they are expressed when needed (through interaction with promoter sequence to initiate or inhibit transcription). - Can work close with other proteins by promoting recruitment of RNA polymerase or blocking.

Question 34

What is an operon?

Answer 34

Group of genes that are under control of same regulatory mechanism and are expressed at the same time.

Question 35

Why are operons beneficial?

Answer 35

Efficient way of saving resources because if certain gene products are not needed, then all of the genes involved in their production will be switched off.

Question 36

What is the lac operon?

Answer 36

Group of three structural genes: lacZ, lacY and lacA, code for three enzymes (beta galactosidase, lactose permease and transacetylase), which are transcribed onto single long molecule of mRNA.

Question 37

What is the regulatory gene involved in the metabolism of lactose?

Answer 37

LacI, located near the operon and codes for a repressor protein that prevents transcription of structural genes in the absence of lactose. Repressor protein is constantly produced and binds to operator.

Question 38

What does the repressor protein binding to the operator region prevent?

Answer 38

Prevents RNA polymerase binding to DNA and beginning transcription. Called down regulation.

Question 39

What is the promoter region?

Answer 39

Section of DNA that is binding site for RNA polymerase.

Question 40

What happens when lactose is present (to initiate lactose metabolism)?

Answer 40

Lactose binds to repressor protein causing it to change shape so it can no longer bind to the operator. RNA polymerase can then bind to the promoter region, so structural genes can then be transcribed and enzymes are synthesised.