Genes And Dna And Protein Synthesis Flashcards
Differences between DNA and mRNA (4)
DNA is longer mRNA is shorter
DNA is double stranded, mRNA is single stranded
DNA has thymine, mRNA has uracil
DNA has deoxyribose sugar, mRNA has ribose sugar
DNA has hydrogen bonds, mRNA does not
Describe the structure of DNA (5)
DNA is a polymer of nucleotides
Each nucleotide is made of a deoxyribose sugar, a phosphate group and a nitrogenous base
There are phosodiester bonds between adjacent nucleotides
DNA has a double helix shape with hydrogen bonds between each polynucleotide strand
There are hydrogen bonds between complementary base pairs. Complementary base pairs are adenine with thymine and guanine with cytosine
Explain why the replication of DNA is describes as semi conservative (2)
Each original polynucleotide strand acts as a template
So in the replicated DNA molecules, one strand is made from the original parental DNA stand and one strand is new.
What is an exon (1)
A sequence of base triplets that codes for the sequence of amino acids/ primary structure of protein.
What is a locus (1)
A fixed position occupied by a gene on a DNA molecule
Define non coding base sequences and describe where non coding base repeats are positioned in the genome (2)
Non coding base sequences is DNA that does not code for a polypeptide
They are located between genes
Compare and contrast the DNA is eukaryotic cells and the DNA in prokaryotic cells. (5)
Similarities
Both DNA are polymers made from identical nucleotide structure ( deoxyribose sugar, phosphate, organic base)
Both have phosphodiester bonds between adjacent nucleotides
DNA in mitochondria/chloroplast is similar to DNA in prokaryotes
Difference
Eukaryotic DNA is linear but prokaryotic DNA is circular
Eukaryotic DNA is longer
Eukaryotic DNA is associated with histones, prokaryotic DNA is not
Eukaryotic DNA contains introns, prokaryotic DNA does not
Explain the position of the band of DNA in tube C (2)
DNA made from one heavy and one light strand
The new DNA stand is made from the lighter 14N
Definition of non overlapping (1)
Each base is part of only one triplet
Give two features of DNA and explain how each one is important in the semi conservative replication of DNA. (2)
Weak hydrogen bonds between complementary base pairs are easily broken so allow two stands to separate/ unzip easily.
Two polynucleotide stands in DNA so both can act as templates
Complementary base pairing allows accurate replication
The arrows in Figure 2 show the directions in which each new DNA strand is
being produced.
Use Figure 1, Figure 2 and your knowledge of enzyme action to explain why the arrows point in opposite directions. (4)
Both polynucleotide strands are anti parallel.
The shapes of the nucleotides on both stands are different shape as they are inverted so shape of 5’ end and 3’ end are different
The active site of DNA polymerase has a unique, specific tertiary structure
The active site is only complementary to the 3’ end of the strand and can only bind to and form an enzyme substrate complex with the 3’ end.
Describe how mRNA is produced from an exposed template strand of
DNA.
Do not include DNA helicase or splicing in your answer.
Free floating RNA nucleotides (contains uracil instead of thymine) are attracted to the exposed bases on the template strand and form hydrogen bonds due to complementary base pairing.
RNA polymerase joins adjacent RNA nucleotides together in a condensation reaction by forming phosphodiester bonds between the ribose sugar of one nucleotide and the phosphate of an adjacent nucleotide.
Mark scheme answer
- (Free RNA) nucleotides form complementary base pairs;
Accept A-U, G-C OR combination of those pairs - Phosphodiester bonds form;
Accept linkages for ‘bonds’ - By (action of) RNA polymerase;
Describe how mRNA is formed by transcription in eukaryotes (5)
(a)
1.
2 of 5
2.
4.
Hydrogen bonds (between DNA bases) break;
Ignore DNA helicase.
Reject hydrolysing hydrogen bonds.
(Only) one DNA strand acts as a template;
(Free) RNA nucleotides align by complementary base pairing;
For ‘align by complementary base pairing’, accept
‘align to complementary bases’ or ‘align by base pairing’.
(In RNA) Uracil base pairs with adenine (on DNA)
OR
(In RNA) Uracil is used in place of thymine;
Do not credit use of letters alone for bases.
RNA polymerase joins (adjacent RNA) nucleotides;
Reject suggestions that RNA polymerase forms hydrogen bonds or joins complementary bases.
(By) phosphodiester bonds (between adjacent nucleotides);
Pre mRNA is spliced to form mRNA as introns are removed from pre mRNA
Describe how a polypeptide is formed by translation of mRNA. (6)
mRNA associates with a ribosome / ribosome attaches to mRNA;
Idea of association is required
Ribosome moves to / finds the start codon / AUG;
tRNA brings / carries (appropriate / specific) amino acid;
Must be explicitly stated and not inferred.
Anticodon (on tRNA complementary) to codon (on mRNA);
Ribosome moves along to next codon;
OR
Ribosome ‘fits’ around two codons / can fit two tRNAs;
Must be explicitly stated and not inferred.
(Process repeated and) amino acids join by peptide bonds / condensation reaction (to form polypeptide);
(Process repeated and) amino acids joined using (energy from) ATP (to form polypeptide);
tRNA is released
Ribosome moves along mRNA to form polypeptide.
Explain the purpose of a stop codon. (2)
Stops translation
So ribosome detaches from mRNA and polypeptide chain
