DNA, genes, protein synthesis

Question 1

State differences between mRNA and tRNA

Answer 1

• mRNA has single helix structure, tRNA has a clover
  shape
• tRNA has an amino acid binding site
• anti codon on tRNA compared to codon on mRNA

Question 2

State similarities between mRNA and tRNA

Answer 2

• both single chain
• both contain ribose sugar
• contain uracil instead thymine

Question 3

Outline differences between DNA in prokaryotes + eukaryotes

Answer 3

prokaryotes - DNA shorter, forms circle, not associated w/ protein mols.
eukaryotes - DNA longer, linear , associates w/ histones to form chromosomes

Question 4

What is a chromosome?

Answer 4

one molecule of DNA, with both polynucleotide strands twisted together to form a double helix wrapped around histone proteins

Question 5

Homologous chromosomes

Answer 5

Pair of chromosomes, one paternal and one maternal which have the same gene loci

Question 6

Haploid number

Answer 6

Number of chromosomes in single set/gametes (n). In humans n = 23

Question 7

Diploid number

Answer 7

Number of chromosomes in within a cell’s nucleus (2n)

In humans = 46

Question 8

Allele

Answer 8

Alternative version/form of a gene

Question 9

What is meant by a mutation?

Answer 9

Change in base sequence of a gene that produces new allele -> diff. sequence of a.acids to be coded for

Question 10

Stages of transcription

Answer 10

• DNA double helix unzipped by DNA helicase => H bonds
  between comp. bases break + strand separates
• one strand acts as template => free RNA nucleotides form H bonds w/ comp. bases + RNA polymerase joins base pairs together
• mRNA detaches from template strand => DNA strands rejoin by comp. base pairing

Question 11

Post-transcriptional processing

Answer 11

Splicing of pre-mRNA to remove introns, as otherwise the mol. is too large to leave the nuclear pore

Question 12

Stages of translation

Answer 12

• Ribosome attaches to starting codon on mRNA
• tRNA (carrying specific a.acid) w/ comp. anticodon pairs w/ codon on mRNA
• ribosome moves along mRNA, brings together 2 tRNa at one time
• 2 a.acids joined by peptide bond using enzyme +
  ATP
• ribosome moves onto 3rd codon, linking 2nd and
  3rd a.acids, 1st tRNA released + free to collect another a.acid from pool
• synthesis continues until stop codon reached when
  mRNA, tRNA + ribosome all separate

Question 13

Role of stop codon

Answer 13

Does not code for an a.acid so ends synthesis of polynucleotide chain

Question 14

What is the genetic code?

Answer 14

a series of bases, arranged in triplets, which code for a sequence of amino acids; it is universal, degenerate and non-overlapping

Question 15

What does universal, degenerate and non-overlapping mean?

Answer 15

universal - code largely universal for living organisms + viruses
degenerate - more than one codon can code for an amino acid
non-overlapping - code is read sequentially in triplets