Gene structure and regulation

Question 1

Define gene

Answer 1

is a length of DNA which codes for a specific protein

Question 2

Define degenerate

Answer 2

When one amino aid may be represented by more than one triplet

Question 3

Every protein that is made in our body has a corresponding …

Answer 3

gene associated with it because the gene is what provides the instructions as to what the amino acid sequence of the protein is.

Question 4

Define the genetic code

Answer 4

is a set of rules that define how info in nucleic acid (RNA and DNA) is translated into proteins and functional RNA molecules. The info in DNA and RNA is stored in a 3 letter code of nucleotide, each triplet code for one amino acid and may provide a specific instruction. So code determines which sequence of nucleotide are translated unto which amino acid.

Question 5

Protein synthesis from genes

Describe transcription

Answer 5

Gene found on the DNA in nucleus is ‘copied’ in the form of a mobile form of genetic material called messenger RNA. The mRNA will leave the nucleus and enter the ribosome.

Question 6

Protein synthesis from genes

Define translation

Answer 6

Is the conversion of a message from one language to another

Question 7

Protein synthesis from genes

Define transcription

Answer 7

Copy a piece of text down

Question 8

Protein synthesis from genes

Describe translation

Answer 8

The genetic code is ‘translated’ into an amino acid sequence. The mRNA arrives at the ribosome, which synthesizes a polypeptide whose amino acid sequence is dictated by the genetic code on the mRNA.

Question 9

Protein synthesis from genes

Characteristics of transcription

Answer 9

• To form copy of gene we use RNA polymerase.
• The enzymes unwinds the DNA and synthesises an RNA strand complementary to the 3’ -> 5’
• The RNA polymerase ‘reads’ the DNA in a 3’ –> 5’ direction but synthesises the RNA strand in a 5’ -> 3’ direction (antiparallel)

Question 10

Protein synthesis from genes

Transcription 
The pre-mRNA is modified in three ways
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Answer 10

• Segments on the pre-mRNA are spliced and removed from the pre-mRNA and the remaining pieces join together. Introns are removed, exons joins together
• A methyl ‘cap’ is added to the 5’ end of the RNA strand
• A poly-A tail (a string of adenine- RNA nucleotide is added ti the 3’ end of the RNA strand)

After this the product is mRNA, known as post-transcription modifications

Question 11

Protein synthesis from genes

Translation 
What occurs
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Answer 11

• The mRNA arrives at the ribosome
• tRNA molecule with the amino acids attached anneals to the mRNA codons via their complementary tRNA antibodies (ie tRNA anitcodon AAA will anneals mRNA codon UUU)
• The amino acids that arrive at the ribosome on their tRNA will detach form the tRNA and be polymerised to form the polypeptide

Question 12

Protein synthesis from genes

Gene regulation

How do all cells have the same genome (genes) but do different things?

Answer 12

This is because different cells express different genes; some are switched on whereas other genes are switched off via a protein blocking the promoter region.

Question 13

Protein synthesis from genes

Gene regulation

Why do all cells have the same genome (genes) but do different things?

Answer 13

prevent cells from producing proteins that arent needed by cell therefore saving resources. Also prevents producing proteins that harm the organism.

Question 14

Protein synthesis from genes

Gene regulation
Define transcription factors

Answer 14

DNA binding proteins that affect the rate of transcription

Question 15

Protein synthesis from genes

Gene regulation
Signalling molecules

Answer 15

may bind to receptor on the cell, which may cause the expression of a gene or the inhibition of that gene

Question 16

Protein synthesis from genes

Gene regulation
Regulatory genes

Answer 16

Transcription factors, and other proteins in the cell that act to regulate the expression of other genes are themselves coded by regulatory genes

Question 17

Protein synthesis from genes
Gene regulation

Define Lac operon

Answer 17

This is the mechanism by which a bacterial gene that synthesisies an enzyme that metabolises lactose is regular.

Question 18

Protein synthesis from genes
Gene regulation

Lac operon regulatory mechanism is designed to..

Answer 18

ensure that the gene is expressed only when there are sufficient amounts of lactose present in the cell.

Question 19

Protein synthesis from genes
Gene regulation

Lac operon
What occurs when there is no lactose

Answer 19

The inhibitory transcription factor binds onto the operator. This inhibits the ability of RNA polymerase to bind onto the promoter.

Question 20

Protein synthesis from genes
Gene regulation

Lac operon
What occurs when there is lactose

Answer 20

lactose binds to the transcription factor, changing its conformation. This changes the binding site of the transcription factor. causing it to detach from the operator. Subsequently, the RNA polymerase is able to bind to the promoter region of the gene and to transcribe the gene.