Genetic control of protein structure and function

Question 1

What is transcription?

Answer 1

The formation of pre-mRNA molecules ,from the DNA that makes up a particular gene, which are then spliced to form mRNA, this is the first stage of protein synthesis

Question 2

What is translation?

Answer 2

The mRNA formed during transcription is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide

Question 3

What is DNA made up of?

Answer 3

Nucleotides that contain a deoxyribose sugar, phosphate group and a nitrogenous base (A,T,C or G)

Question 4

How do the nucleotides join together to form polynucleotides?

Answer 4

By creating a sugar-phosphate backbone, a phosphate group of one nucleotide joins to the sugar of another

Question 5

How do two DNA polynucleotide stands join?

Answer 5

Hydrogen bonding between the complimentary bases (A-T, C-G)

Question 6

What are genes?

Answer 6

Sections of DNA that are found on chromosomes that code for a specific protein (polypeptide)

Question 7

What are proteins made of?

Answer 7

Chains of amino acids

Question 8

What determines the order of amino acids in a protein?

Answer 8

The order of nucleotide bases in a gene

Question 9

What is meant by a triplet code?

Answer 9

A sequence of 3 bases (e.g. GTC=one amino acid) also known as a DNA /Base triplet or codon

Question 10

Where Is DNA found in the cell?

Answer 10

Nucleus

Question 11

What is the function of ribosomes and where are they found in the cell?

Answer 11

Protein synthesis and cytoplasm

Question 12

What is RNA made up of?

Answer 12

Nucleotides of a ribose sugar, phosphate group and a base (A,U,C,G)

Question 13

What is the different in structure of DNA and RNA?

Answer 13

DNA is a double stranded twisted helix whereas RNA is single stranded

Question 14

What is mRNA used for and where is it made?

Answer 14

Carries the genetic code for the DNA in the nucleus to the cytoplasm, via a nucleic pore, where it’s used to make proteins during translation. It is made in the nucleus during transcription and is formed from pre-mRNA after it has been spliced to remove any introns (non-coding DNA)

Question 15

What is an exon?

Answer 15

Coding section of DNA

Question 16

What is the role of the enzyme DNA helicase during transcription?

Answer 16

It breaks the hydrogen bonds between the bases on a specific region of DNA, causing the two strands to separate and expose the nucleotide bases in that region

Question 17

What is the function of the enzyme RNA polymerase during transcription?

Answer 17

Moves along one of the two DNA strands(template strand) causing the nucleotides on this strand to join with the individual complementary nucleotides free in the nucleus

Question 18

How does RNA polymerase know when to stop transcribing the pre mRNA?

Answer 18

When it reaches a stop codon it stops making pre mRNA and detaches from the DNA

Question 19

How is pre-mRNA changed into mRNA?

Answer 19

Introns are removed via splicing , leaving the remaining exon sections to rejoin in a variety of differ erm combinations

Question 20

What happens to the mRNA after the splicing process?

Answer 20

It moves out of the nucleus via a nuclear pore and attaches to a ribosome in the cytoplasm, which marks the start of translation

Question 21

What is tRNA and what is its function?

Answer 21

A single polynucleotide strand folded into a clover shape in which hydrogen bonds between specific base pairs hold the molecule in this shape. It is involved in translation and carries the amino acids that are used to make proteins to the ribosome

Question 22

How can a tRNA molecule carry an amino acid?

Answer 22

Each molecule had a specific sequence of 3 bases at one end called an anti codon, and have an amino acid binding site at the other end

Question 23

Where is tRNA found?

Answer 23

Cytoplasm of cells

Question 24

What are the different in bases in DNA and RNA?

Answer 24

DNA contains A,T,C,G whereas RNA contains A,U,C,G

Question 25

Where does transcription occur?

Answer 25

Nucleus

Question 26

Where does translation occur?

Answer 26

At ribosomes in the cytoplasm

Question 27

What is an anticodon?

Answer 27

A sequence of 3 adjacent nucleotides on a molecule on tRNA that is complimentary to a particular codon on a mRNA molecule

Question 28

What are the stages of translation?

Answer 28

#  Ribosome attaches itself to the starting codon at one end of the mRNA
# Complementary tRNA molecule pairs up with the sequence on mRNA via it's anticodon, and carries a specific amino acid
#A tRNA with a complementary anticodon pairs up with next codon on mRNA, carrying another amino acid
#Amino acids joined together by peptide bonds
#First tRNA molecule detaches itself from it's amino acid
# Ribosome moves along mRNA by one codon
#Continues to move along mRNA until it reaches a stop codon
#Polypeptide chain is released and folded into it's correct shape

Question 29

What is meant by a mutation?

Answer 29

A change in the sequence of bases in DNA, which could result in a change to the quantity or structure

Question 30

When are mutations passed on to the next generation?

Answer 30

If they occur in the gametes (sex cells)

Question 31

What is meant by a gene mutation?

Answer 31

Any change to one or more nucleotide bases/rearrangement of bases in DNA

Question 32

What is substitution?

Answer 32

The type of gene mutation in which a nucleotide in DNA is replaced by another nucleotide with a different base

Question 33

What are the 3 types of substitution?

Answer 33

Nonsense, mis-sense and silent mutations

Question 34

What is a nonsense mutation?

Answer 34

When the base change results in the formation of a stop codon, marking the end of a polypeptide chain which may lead to a non-function protein

Question 35

What is a mis-sense mutation?

Answer 35

When the base change results in a different amino acid being coded for

Question 36

What is a silent mutation?

Answer 36

When the substituted base still codes for the same amino acid before, due to the degenerate nature of the genetic code

Question 37

Why is the genetic code known as being degenerated?

Answer 37

Amino acids have more than one codons that code for them e.g. GTC and GTT both code for glutamine

Question 38

What is deletion?

Answer 38

When a nucleotide is lost from a DNA sequence, creating a frame shift. If they occur at the start of a sequence, they will have a huge effect as an entirely different protein may be translated, or it may be non-functioning

Question 39

What is meant by a frame-shift?

Answer 39

When the reading frame that contains each 3 letters of the code has been shifted to the left by one letter e.g.

T G C A G G TAC
Removal of guanine from first codon

Question 40

What are the causes of mutations?

Answer 40

• Can occur spontaneously during an error in DNA replication
• Genetic inheritance
• Mutagenic agents: High energy radiation (e.g. UV) and chemicals (e.g. tar)

Question 41

Which genes are responsible for the control of cell division?

Answer 41

Proto-oncogenes and tumour suppressor genes

Question 42

What is the role of proto-oncogenes?

Answer 42

They stimulate cell division (can cause tumour or cancer to develop) They may be mutated into oncogenes which can affect cell division by:

• Permanently activating receptor protein on CSM so cell division occurs even without growth factors
• They may code for a growth factor that is then produced in excessive amounts

Question 43

What is the role of tumour suppressor genes?

Answer 43

They slow down cell division (opposite to proto-oncogenes) It maintains the normal rate of cell division and prevents tumour formation

Question 44

What happens if a tumour suppressor gene is mutated?

Answer 44

Becomes inactivated, meaning it stops inhibiting cell division and allows the rate of it to increase