DNA, genes and protein synthesis

Question 1

What is a gene

Answer 1

a section of DNA that contains the coded information for making polypeptides and functional RNA

Question 2

What is the genetic code

Answer 2

the information encoded in the sequences of nucleotide triplets, called codons, which are translated into amino acid sequences and thus proteins

Question 3

What 2 things do genes code for

Answer 3

• amino acid sequence of polypeptides

- functional RNA

Question 4

What are features of the genetic code

Answer 4

Universal - almost all triplets (codons) can for the same amino acid across all living organisms

Degenerate - most amino acids are coded for by more than one codon

Non-overlapping - each base is only read once and in one direction

Question 5

Whats the difference between a genome and a proteome

Answer 5

Genome - is the complete set of genes in a cell

Proteome - is the full range of proteins produced by the genome

Question 6

What are histones

Answer 6

proteins that associate with long DNA molecules coil up to form chromosomes

Question 7

What are homologous chromosomes

Answer 7

the fusion of a sperm (paternal chromosomes) and an egg (maternal chromosomes) which contribute one complete set of chromosomes for the offspring

Question 8

What is the structure of a chromosome

Answer 8

2 threads of genetically identical DNA molecules called chromatids that are joined together at the centromere

Question 9

What is an allele

Answer 9

one of a number of alternative forms of a gene

Question 10

Describe the structure of RNA

Answer 10

made up of a phosphate group, a hydrogenous base and a ribonucleic acid

Question 11

Compare DNA and RNA

Answer 11

DNA:

• double helix
• double polypeptide chain
• adenine binds to thymine

RNA:

• single helix
• single polypeptide chain
• adenine binds to uracil

Both have a sugar phosphate back bone

Question 12

What is a codon

Answer 12

a sequence of 3 nucleotides that code for 1 amino acid in mRNA

Question 13

Compare mRNA and tRNA

Answer 13

mRNA:

• functions in the nucleus of the cell
• carries DNA sequence from nucleus to the ribosomes
• single stranded made up of codons which are a specific amino acid

tRNA:

• functions in the cytoplasm of the cell
• cloverleaf shape made up of 3 anticodons which are specific to 1 amino acid

Question 14

Define transcription

Answer 14

the process of making pre-mRNA by using a part of the DNA as a template in the nucleus

Question 15

What is the process of transcription

Answer 15

• DNA polymerase breaks down the hydrogen bonds between nucleotides and DNA unwinds
• free RNA nucleotides bind to the complementary based pairs on the DNA template
• the RNA nucleotides bind together and a sugar phosphate back bone forms between them making pre-mRNA
• the pre-mRNA gets spliced and the introns get removed
• the exons are joined by splicosomes
• mRNA moves out a nuclear pore

Question 16

Compare an intron and an exon

Answer 16

intron - section removed from pre-mRNA as they don’t code for proteins

exons - section of a gene that codes for proteins

Question 17

Define translation

Answer 17

is where mRNA is turned into a series of amino acids bound together with peptide bonds

Question 18

What do start and stop codons do

Answer 18

start codons - tell the tRNA where to start ‘initiation’

stop codons - tell the tRNA where to stop ‘termination’

Question 19

What is the process of translation

Answer 19

• small ribosome sub unit binds to the 5’ end of the mRNA
• Initiation - tRNA binds to the start codon
• large ribosome sub unit binds to small ribosome sub unit
• tRNA with anticodon and the specific amino acid moves into the ribosome and pairs with the complementary base codon on the mRNA
• the ribosome moves along the mRNA to the next codon where another tRNA moves into the ribosome
• Elongation - as the tRNA is released from the ribosome the amino acids bind with peptide bonds
• this continues until it reaches the stop codon at the 3’ end - Termination
• the ribosome, mRNA and tRNA separate the polypeptide chain is complete
• the chain begin folding till the quaternary structure is formed

Question 20

Why does DNA polymerase (enzyme) work in different directions when a new DNA strand is being produced

Answer 20

• DNA has antiparallel strands
• the enzyme has a complementary shape to the shape of the nucleotide
• thus it can only bind to the nucleotide with the shape complementary to the 3’ end of the developing strand