Topic 4A: Genetic Information, Variation and Relationships Between Organisms Flashcards
Describe how mRNA is formed by transcription in eukaryotes. [5]
- Hydrogen bonds (between DNA bases) break;
- (Only) one DNA strand acts as a template;
- (Free) RNA nucleotides align by complementary base pairing;
- (In RNA) uracil is used instead of thymine;
- RNA polymerase joins (adjacent RNA) nucleotides;
- (By) phosphodiester bonds;
- Pre-mRNA is spliced (to form mRNA)
Describe how a polypeptide is formed by translation of mRNA. [6]
- (mRNA attaches) to ribosome;
[2. Ribosome finds start codon] - (tRNA) anticodons (bind to) complementary (mRNA) codons;
- tRNA brings a specific amino acid;
- Amino acids join by peptide bonds;
- with the use of ATP;
- tRNA released (after amino acid joined to polypeptide);
- The ribosome moves along the mRNA codon by codon to form the polypeptide
What is the role of RNA polymerase in transcription? [1]
- Joins (adjacent) nucleotides using phosphodiester bonds to form a strand of mRNA
Name the organelle involves in translation. [1]
- Ribosome
Give four structural differences between a molecule of mRNA and a molecule of tRNA. [4]
- mRNA is linear chain, tRNA is cloverleaf;
- mRNA does not have an amino acid binding site, tRNA does;
- mRNA has more nucleotides;
- (Different) mRNAs have different lengths, all tRNAs are similar length;
- mRNA has codons, tRNA has an anticodon
Describe how the production of mRNA in a eukaryote cell is different from the production of mRNA in a prokaryote cell. [2]
- Pre-mRNA produced in eukaryote, mRNA produced in prokaryote;
- Splicing only occurs in eukaryote;
- Introns removed in eukaryote, not present in prokaryote
Recombinant DNA technology can involve the transfer of fragments of human DNA into bacteria. The bacteria are then used to produce human proteins.
Give two reasons why bacteria are able to use human DNA to produce human proteins. [2]
- The genetic code is universal;
- (The mechanism of) transcription is universal;
- (The mechanism of) translation is universal
Compare and contrast the DNA in the nucleus of a plant cell with the DNA in a prokaryotic cell. [5]
Similarities:
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bonds;
Differences: (plant DNA vs prokaryote DNA)
3. (Associated with) histones vs no histones;
4. Linear vs circular;
5. No plasmids vs plasmids;
6. Introns vs no introns;
7. Longer vs shorter
HIV attaches to a specific protein receptor on helper T cells. A low percentage of people have a mutation of the of the CCR5 gene which codes for this protein receptor. This mutation results in a non-functional protein receptor.
a. Explain how this mutation can result in the production of a non-functional protein receptor. [4]
b. People with the CCR5 mutation show a greater resistance to developing AIDS.
Explain why. [2]
a. 1. Change in DNA base sequence;
2. Change in primary structure;
3. Alters (position of) hydrogen/ionic/disulphide bonds;
4. Change in tertiary structure
b. 1. (Receptor) is not complementary (to attachment protein)
2. No destruction of (helper) T cells
OR
No replication of virus
Describe how mRNA is produced from an exposed template strand of DNA.
Do not include DNA helicase or splicing in your answer. [3]
- (Free RNA) nucleotides form complementary base pairs;
- Phosphodiester bonds form;
- By RNA polymerase
Define the term exon. [1]
- Base sequence coding for polypeptide
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Give two reasons why. [2]
- Triplets code for same amino acid;
- Occurs in introns
What is the name given to any factor that can increase the rate of mutation? [1]
- Mutagenic agent
The genetic code is described as degenerate.
What is meant by this? [1]
- More than one codon codes for a single amino acid
Give the two types of molecule from which a ribosome is made. [1]
- Ribosomal RNA and protein
Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer. [3]
- mRNA binds to ribosome;
- Holds two codons at a time;
- (Allows) tRNA with anticodons to bind;
- (Catalyses) formation of peptide bond (between amino acids);
- Moves along (mRNA to the next codon)
In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA.
Explain why. [2]
- Introns (in pre-mRNA);
- Splicing
In a eukaryotic cell, transcription results in a molecule of pre-mRNA that is modified to produce mRNA. In a prokaryotic cell transcription produces mRNA directly.
Explain this difference. [2]
- Pre-mRNA contains introns;
- These regions are removed from pre-mRNA
What is the proteome of a cell? [1]
- The full range of different proteins that a cell is able to produce
Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide.
Do not include descriptions of transcription and splicing in your answer. [5]
- mRNA attaches to a ribosome;
- Ribosome finds the start codon;
- tRNA brings specific amino acid;
- Anticodon (on tRNA complementary) to codon (on mRNA);
- Ribosome moves along to next codon;
- (Process repeated and) amino acids joined by peptide bonds (to form polypeptide)
Describe how the process of meiosis results in haploid cells.
Do not include descriptions of how genetic variation is produced in meiosis. [4]
- DNA replication during interphase;
- Two (nuclear) divisions;
- Separation of homologous chromosomes (in first division);
- Separation of sister chromatids (in second division)
What is the biological importance of reducing the chromosome number when the cell divides by meiosis? [2]
- Later fertilisation;
- Restoring diploid
A scientist crossed two strains of fungus. To cross these strains.
Describe and explain three ways in which the scientist would ensure he used aseptic techniques. [3]
- Wash hands to kill microbes;
- Burning Bunsen close by to create upward current of air;
- Disinfect bench to kill microbes;
- Flame instrument to kill microbes;
- Lift lid slightly to prevent entry of microbes
Give two differences between mitosis and meiosis. [2]
Mitosis vs meiosis
1. One division vs two divisions;
2. (Daughter) cells genetically identical vs daughter cells genetically different;
3. Two cells produced vs four cells produced;
4. Diploid to diploid vs diploid to haploid;
5. Separation of homologous chromosomes only in meiosis;
6. Crossing over only in meiosis
Give one reason why butterfly eggs produced by meiosis are genetically different. [1]
- Independent segregation
OR
Crossing over
What is an allele? [1]
- Version of a gene
Explain how the chromosome number is halved during meiosis. [2]
- Homologous chromosomes (pair);
- One of each (pair) goes to each (daughter) cell
Describe the process of crossing over and explain how it increases genetic diversity. [4]
- Homologous pairs of chromosomes form a bivalent;
- Chiasmata form;
- (Equal) lengths of (non-sister) chromatids are exchanged;
- Producing new combinations of alleles
Apart from mutation, crossing over and independent segregation explain one other way genetic variation within a species is increased. [2]
- Random fertilisation;
- (Produces) new allele combinations
