Topic 6 - Inheritence, variation and evolution - Protein synthesis

Question 1

What is each nucleotide made up of?

Answer 1

• phosphate group
• pentose sugar
• nitrogenous base

Question 2

How does the structure of DNA and RNA nucleotides alter?

Answer 2

• both have same phosphate group
• in DNA nucleotides pentose sugar is deoxyribose - RNA nucleotides pentose sugar is ribose
• in RNA uracil (U) replaces thymine (T)

Question 3

What are the four nitrogenous bases?

Answer 3

• adenine (A)
• thymine (T)
• cytosine (C)
• guanine (G)

Question 4

What are the complimentary base pairings in DNA?

Answer 4

• adenine pairs with thymine - A pairs with T
• cytosine pairs with guanine - C pairs with G

Question 5

What are the complimentary base pairings in RNA?

Answer 5

• adenine pairs with Uracil - A pairs with U
• cytosine pairs with Guanine - C pairs with G

Question 6

What is the sequence of three bases?

Answer 6

sequence of three bases is the code for a single specific amino acid

Question 7

What do the order of bases control?

Answer 7

• order and types of amino acids that are joined together in polypeptide chain
  polypeptide chains (the amino acid sequences) then form a particular type of protein
• order of bases in DNA eventually determines which proteins are produced

Question 8

Difference between mRNA and DNA?

Answer 8

• mRNA much shorter than DNA - it is only a single gene long
• only a single strand rather than a double strand like DNA
• nstead of thymine contains uracil

Question 9

Why do we need mRNA?

Answer 9

• ribosomes have to read sequence of bases to make protein - genes contain these sequences
• ribosomes exist outside the nucleus
• genes are within DNA in nucleus - DNA cannot leave the nucleus - too big
• mRNA acts as messenger between DNA and ribosome - carries code between them

Question 10

How does transcription work?

Answer 10

• RNA polymerase enzyme binds to start of gene
• two strands of DNA split apart - bases exposed
• RNA polymerase moves along DNA - reading bases one by one so it can make corresponding mRNA strand
• as RNA polymerase moves up the DNA - DNA strand closes behind it
• when mRNA strand complete - RNA molymerase detaches from DNA - DNA strand completely closes
• mRNA leaves nucleus and goes to ribosomse

Question 11

How does translation work?

Answer 11

• mRNA strand and ribosome bind together
• amino acids brought to ribosome by tRNA (transfer RNA)
• tRNA have amino acid at top and anti-codon at bottom - anticodon is set of three bases complementary to a specific codon on mRNA
• tRNAs bring correct amino acid to ribosome in correct order so they can be joined together
• when ribosome reaches end of mRNA - complete chain of amino acids formed
• amino acid chain detaches from ribosome and folds up to make a protein