8.DNA, Genes, Protein Synthesis

Question 1

What is a gene

Answer 1

Base sequence of DNA that codes for the amino acid sequence of polypeptides and functional RNA

Question 2

What’s the reasoning for three bases coding for one amino acid

Answer 2

Only 20 different amino acids regularly occur
Each must have own code of bases on dna
Only 4 bases present in dna
If each base coded for one amino acids, only be 4 amino acids
Using three bases, 64 different codes (4^3)

Question 3

What does degenerate code mean

Answer 3

Most amino acids coded for by more than one triplet

Question 4

Features of genetic code

Answer 4

Degenerate code
Non overlapping
Universal

Question 5

What’s a stop codon

Answer 5

Three bases together that don’t code for a amino acid and they mark end of polypeptide chain

Question 6

What’s an Exxon and intron

Answer 6

Exon-coding sequences for amino acids

Intron-non coding for amino acids

Question 7

What’s a locus

Answer 7

The particular position where a gene is located on a particular sector of dna

Question 8

What’s the difference between prokaryotic dna and eukaryotic dna

Answer 8

Pro- short, circular and not associated with protein molecules so therefore no chromosomes

Eu-longer, linear and associated with histones to form chromosomes, mitochondria and chloroplasts contain own dna similar to prokaryotic dna

Question 9

What’s a chromatid

Answer 9

When dna has replicated, the two identical dna molecules are joined at a single point

Question 10

What’s a homologous pair

Answer 10

When one chromosome is from mum (maternal) and the same one is from dad (paternal)

Same chromosome but will have different alleles

Question 11

What’s an allele

Answer 11

Alternative form of gene

Two different forms of genes-different forms are alleles

Allele inherited from each parent

Question 12

What’s the danger of change in base sequence of gene

Answer 12

Produces new allele =mutation
Different polypeptide due to different amino acid sequence
Different protein
May not be functional
If enzyme produced, new shape not fit substrate
Enzyme not function=serious consequence for organism

Question 13

What is mRNA

Answer 13

Messenger rna

Transfers dna code from nucleus into cytoplasm leaves via nuclear pores

Question 14

What’s a genome

Answer 14

Complete set of genes in a cell, including those in mitochondria/chloroplasts

Question 15

What’s a proteome

Answer 15

Range of proteins produced by genome, called complete proteome where proteome refers to proteins produced by a given type of cell under certain set of conditions

Question 16

What makes up the mononucleotide of ribonucleic acid

Answer 16

Ribose (pentose sugar)
An organic base (A,G,C,U
Phosphate group

Question 17

What is messenger rna structure

Answer 17

• Long strand arranged in single helix
• Base sequence is determined by bases on length of dna is process called transcription
• structure is suited to function as possess information in form of codons and the sequence determines specific polypeptide made

Question 18

What is tRNA structure

Answer 18

• Relatively small molecule made up of around 80nucleotides
• Single stand folded into clover leaf shape one end extends beyond the other (point of amino acid attachment)
• anticodon at opposite end-three coding bases

Question 19

What happens during transcription

Answer 19

• Enzyme acts on specific region of DNA, two strand separate expose nucleotide bases in that region
• template strand baes pair with complimentary bases from pool
• enzyme rna polymerase moves along strand and joins nucleotides together to form pre mRNA molecule
• as RnA polymerases adds one nucleotide at a time, DNA strands rejoin behind it, only 12 bases exposed at once
• when RNA reaches stop triplet it detached, pre mRNA completed

Question 20

What happens in splicing

Answer 20

• Transcription results in pre-mRNA which contains introns and exons
• introns prevent synthesis of polypeptide
• introns are removed and functional Exxon’s are joined together in process called splicing
• leave nucleus via nuclear pore in nuclear envelope, attach to ribosome in cytoplasm
• only happens in eukaryotic cells

Question 21

What happens in translation/synthesising polypeptide

Answer 21

• ribosome attaches to one end of mRNA
• tRNA molecule complimentary anticodon sequence moves to ribosome and pair with codon on mRNA, tRNA carries specific amino acid
• tRNA molecules pairs with next codon on mRNA, ribosome moves up mRNA bringing together two tRNA molecules at any one time an pairing them with mRNA
• amino acids are joined by peptide bonds using enzyme and atp
• as the second and third amino acids are joined the first tRNA is released and free to collect another amino acid from pool in cell
• process continues until polypeptide chain is built
• synthesis continues until ribosome reaches stop codon and last tRNA is released

Question 22

How is a protein assembled

Answer 22

• sometimes only polypeptide chain is a functional protein, sometimes many are linked together to be functional
• secondary folding, tertiary folding, non proteins being added to quarternary