Section 4 - Unit 8: DNA, Genes & Protein Synthesis Flashcards
In which of the following are hydrogen bonds present in: DNA, mRNA, tRNA (3 marks)
- DNA
- tRNA
Give two ways in which the structure of a molecule of tRNA differs from the structure of a molecule of mRNA (2 marks)
- tRNA has an amino acid binding site
- tRNA has hydrogen bonds between base pairs
Describe the part played by mRNA in protein synthesis (3 marks)
Any three from:
- Carries coded information about the sequence of amino acids
- Copied from DNA/gene
- Code is in sequence of bases for one amino acid
- Moves out of nucleus
- Into the ribosomes
Explain how a gene codes for a protein (2 marks)
- Base sequence on DNA
- Determines sequence of amino acids
Explain what homologous chromosomes are (2 marks)
- Pairs of chromosomes
- With genes for same features
- At same loci
Define gene (2 marks)
- A base sequence of DNA that codes for the amino acid sequence of a polypeptide
- And a functional RNA (including ribosomal RNA and tRNAs).
State two differences between prokaryotic and eukaryotic DNA (2 marks)
- Short vs long
- Circular vs linear
What is the name of a position of a gene on a chromosome? (1 mark)
- Locus
Describe how mRNA is produced in the nucleus of a cell (6 marks)
- Helicase
- Breaks hydrogen bonds
- One DNA strand acts as template
- RNA nucleotides attracted to exposed bases
- According to base pairing rule
- RNA polymerase joins (RNA) nucleotides together
- Pre-mRNA spliced to remove introns
Explain why the genetic code is described as being universal (1 mark)
- In all organisms, the same triplet codes for the same amino acid
What is the maximum number of different DNA triplets that can be made (1 mark)
64
Name the process that removes base sequences from pre-mRNA to form mRNA (1 mark)
Splicing
Explain why the mutation of an exon can lead to the production of a non-functional protein (3 marks)
Any 3 from:
- Mutation changes triplets
- Which change the amino acid sequence after this
- And affects the hydrogen bonding
- Which changes the tertiary structure of protein (so non-functional)
Explain what effect a mutation of the intron has on the protein (2 marks)
- Introns non-coding
- So no effect on protein
Explain why the genetic code is described as being degenerate (1 mark)
- An amino acid can be coded for by more than one triplet
Explain what is meant by a codon (2 marks)
- Three bases on mRNA
- That code for an amino acid
Explain the role of RNA polymerase during transcription (1 mark)
- To join nucleotides together to form mRNA
Explain how a change in the DNA base sequence for a protein may result in a change in the structure of the protein (3 marks)
- Change in amino acid sequence
- Leads to a change in hydrogen/ionic/disulphide bonds
- Which alters tertiary structure
Explain the difference between pre-mRNA and mRNA (1 mark)
- Pre-mRNA contains introns vs mRNA only contains exons
Starting with mRNA, describe how the process of translation leads to the production of a polypeptide (4 marks)
Any four from:
- mRNA attaches to ribosome
- The codon on mRNA
- Binds to an anti-codon on tRNA
- Each tRNA brings a specific amino acid
- Bases on mRNA determines order of amino acids
- Formation of peptide bonds by condensation reactions
State the role of RNA polymerase in transcription (1 mark)
- Attaches nucleotides to form a strand
Describe the role of tRNA in the process of translation (3 marks)
Any 3 from:
- Anticodon complementary to codon
- Specific amino acid
- Carried to ribosome
- Correct sequence of amino acids along polypeptide
Explain how a change in a sequence of DNA bases could result in a non-functional enzyme
- Change in sequence of amino acids/primary structure
- Change in hydrogen/ionic/disulfide bonds leads to change in tertiary structure/active site of enzyme
- Substrate cannot bind/no enzyme-substrate complexes form
Use your knowledge of DNA structure and function to explain how it’s possible for humans and animals to be different even though they have very similar percentages of each base (2 marks)
- Different genes
- So triplets are in a different order
- So different amino acids are coded for
Explain how a cancer drug could prevent DNA replication (2 marks)
- Drug has similar shape
- So complementary base pairing cannot take place
Explain why a mutation involving the deletion of a base may have a greater effect than one involving substitution of one base for another (3 marks)
- Deletion causes frame shift
- So changes many amino acids
- Substitution alters one codon
- But degenerate nature means that the same amino acid can be coded for
Describe how two amino acids differ from one another (1 mark)
- Different R groups
Suggest how a mutation can lead to the production of a protein that has one amino acid missing (1 mark)
- Loss of 3 bases
Name the enzyme used to convert mRNA into DNA (1 mark)
- Reverse transcriptase
Describe how a polypeptide is formed by translation of mRNA (6 marks)
- mRNA attaches to ribosomes
- (tRNA) anticodons (bind to) complementary (mRNA) codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds
- (Amino acids join together) with the use of ATP
- tRNA released (after amino acid joined to
polypeptide) - The ribosome moves along the mRNA to form
the polypeptide
Describe the role of a ribosome in the production of a polypeptide (3 marks)
- mRNA binds to ribosome
- Idea of two codons/binding sites
- (Allows) tRNA with anticodons to bind/associate
- (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules)
- Moves along (mRNA to the next codon)/translocation described
