4 Genetic information, variation and relationships between organisms EQs Flashcards
Give the two types of molecule from which a ribosome is made (2 marks)
RNA and Protein
Describe the role of tRNA in the process of translation (3 marks)
- Anticodon complementary to codon
- specific amino acid transferred to ribosome,
- correct sequence of amino acids polypeptide
Describe the role of a ribosome in the production of a polypeptide (3 marks)
- mRNA binds to ribosome,
- tRNA with complementary anticodon forms base pairs with the mRNA codon as there are two binding sites
- peptide bond forms between amino acids via condensation reaction
- moves along to next codon
Give two differences between structure of mRNA and tRNA (2 marks)
- mRNA does not have hydrogen bonds, tRNA does
- mRNA is linear, tRNA is cloverleaf
What is the proteome of a cell? (1 mark)
Range of different proteins that a cell is able to produce
Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule. (2 marks)
- Condensation reaction
- Between phosphate and deoxyribose
- Catalysed by DNA polymerase
Name the protein associated with DNA in a chromosome. (1 mark)
Histone
The nucleus and a chloroplast of a plant cell both contain DNA.
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus (3 marks)
In chloroplasts:
1. DNA shorter
3. DNA circular not linear
4. Not associated with histones, unlike nuclear DNA
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Give two reasons why. (2 marks)
- Triplets code for same amino acid
- Occurs in introns
DNA is a polymer of nucleotides. Each nucleotide contains an organic base.
Explain how the organic bases help to stabilise the structure of DNA. (2 marks)
- Hydrogen bonds between the base pairs holds two strands together
- Many hydrogen bonds provides strength
Suggest one advantage of showing the genetic code as base sequences on mRNA, rather than triplets on DNA. (1 mark)
Because ribosomes assemble polypeptides using mRNA code
What name is given to a group of three bases on mRNA that codes for an amino acid? (1 mark)
Codon
In a eukaryotic cell, the structure of the mRNA used in translation is different from the
structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecules. (2 marks)
- mRNA has no introns
- because of splicing
Why is the genetic code described as being universal? (1 mark)
In all organisms the same triplet codes for the same amino acid
A scientist investigated possible relationship between air
pollution and the size of seeds produced by one species of tree.
He was provided with a very large number of seeds collected from a population of
trees in the centre of a city and also a very large number of seeds collected from a
population of trees in the countryside.
Describe how he should collect and process data from these seeds to investigate
whether there is a difference in seed size between these two populations of trees.
[5 marks]
- Use random sample of seeds from each population
- Use large enough sample to be representative of whole population;
- Measure the mass
- Calculate a mean and standard deviation for each population
- Use the (Student’s) t-test;
- Analyse whether there is a significant difference
between the means of the two populations;
Describe how a gene is a code for the production of a polypeptide. (3 marks)
- Because base sequence;
- In triplets
- Determines order of amino acid sequence
Define the term exon (1 mark)
Base coding for sequence of amino acids
What are three differences between DNA in the nucleus
of a plant cell and DNA in a prokaryotic cell? (3 marks)
- Introns v no introns;
- Linear v circular;
- No plasmids v plasmids;
Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome. (2 marks)
- DNA that does not code for sequences of amino acids.
- Positioned between genes
Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas. (1 mark)
Differences in base sequences
What is a homologous pair of chromosomes? (1 mark)
Two chromosomes that carry the same genes
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation. (3 marks)
- tRNA brings specific amino acid to ribosome
- Anticodon on tRNA binds to codon on mRNA
- Amino acids join by condensation reaction to form peptide bond
Describe how mRNA is produced from an exposed template strand of
DNA. (3 marks)
- Free RNA nucleotides form complementary base pairs
- Phosphodiester bonds form
- By action of RNA polymerase;
Describe how mRNA is formed by transcription in eukaryotes. (5 marks)
- 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 base pairs with adenine on DNA
- 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 marks)
- mRNA attaches to ribosomes
- tRNA anticodons bind to complementary mRNA codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds
- tRNA released after amino acid joined to polypeptide
- The ribosome moves along the mRNA to form the polypeptide
What does degenerate mean? (1 mark)
More than one codon codes for a single amino acid
Explain how non-disjunction mutation changes the number of chromosomes (2 marks)
- In meiosis
- Chromosomes don’t separate
Apart from mutation, explain one other way genetic variation within a species is increased. (2 marks)
- Random fusion of gametes
- Produces new allele combinations
Explain how the chromosome number is halved during meiosis. (2 marks)
- Homologous chromosomes pair
- One of each pair goes to each daughter cell / to opposite
poles;
Describe the process of crossing over and explain how it increases genetic
diversity. (4 marks)
- Homologous pairs of chromosomes associate
- Chiasmata form
- Equal lengths of non-sister chromatids
- Producing new combinations of alleles;
Explain why all the cells of the body will have this mutation. (2 marks)
- All cells derived from a single cell by mitosis;
- Mitosis produces genetically identical cells
What is meant by ‘species richness’? (1 mark)
A measure of the number of different species in
a community;
Suggest one consideration the scientists had taken into account to make sure their method allowed them to identify accurately the species to which each belonged. [1 marks]
Use photographs / use a key
Give two ways the students would have ensured their index of diversity was
representative of each habitat. (2 marks)
- Random samples;
- Large number of samples
Suggest why biodiversity decreases when farmers use larger fields. (1 mark)
Fewer species
Farmers are now being encouraged to replant hedges on their land.
Suggest and explain one advantage and one disadvantage to a farmer of replanting hedges on her farmland. (2 marks)
Advantage -
1. Greater (bio)diversity so increase in predators of
pests
Disadvantage -
2. Reduced land area for crop growth
Explain how human mass at birth is affected by stabilising selection (3 marks)
- Extreme mass babies least likely to survive
- to reproduce and so
- less likely to pass on their
alleles for extreme mass at birth
The scientists calculated a P value of 0.03 when testing their null hypothesis.
What can you conclude from this result? Explain your answer. (2 marks)
- Probability that difference is due to chance is less than 0.05
- Reject null hypothesis;
Name one source of DNA from an extinct animal? (1 mark)
Bone/skin/preserved remains / museums;
Other than hunting, suggest two reasons why populations might show very low levels
of genetic diversity. (2 marks)
- Population might have been very small/genetic bottleneck;
- Population might have started with small number of individuals / founder effect;
- Inbreeding;
Explain why it is more useful to calculate an index of diversity than to record species
richness. (2 marks)
- Index of diversity also measures population size of each species
- So useful because may be many of some species
Suggest one reason the scientists used biomass instead of the number of individuals of each plant species when collecting data to measure diversity (1 mark)
too time consuming to count individuals
Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria becoming a common cause of infection acquired when in hospital (3 marks)
- some bacteria have alleles for resistance
- resistant bacteria survive and reproduce
- more antibiotics used in hospital
Give three differences between DNA molecules and tRNA molecules? (3 mark)
- Deoxyribose v ribose;
- Double-stranded v single-stranded;
- Many nucleotides v few ;
- Thymine v uracil;
- Double helix v clover (leaf structure);
- Does not bind to amino acid v does bind to amino acid;
- No exposed bases v anticodon;
Suggest why amino acid replacement changes the properties of a protein? (2 marks)
- changes the bond
- which changes the tertiary structure
The total number of bases in the DNA of the α-polypeptide gene is more than 423.
Give two reasons why there are more than 423 bases. (2 marks)
- Non coding DNA
- Addition of base by mutation
Farmers clear tropical forest and grow crops instead. Explain how this causes the
diversity of insects in the area to decrease. (3 marks)
- Lower diversity of plants
- Few sources of food
- Few habitats/ niches;
The spotted owl is a bird. Numbers of spotted owls have decreased over the past
50 years. Explain how this decrease may affect genetic diversity (2 marks)
- Reduced (genetic diversity);
- As fewer different
alleles / reduced gene pool;
State the function of the protein found in chromosomes (1 mark)
fixes the DNA into position
Explain how the considerable length of a DNA molecule is compacted into a chromosome (1 mark)
looped and coiled a number of times
Distinguish between a codon and an anticodon (2 marks)
- codon is a triplet of bases of mRNA that codes for an amino acid
- anticodon is the triplet of bases on a tRNA that is complementary to a codon
Explin the advantage of DNA being a stable molecule (1 mark)
ensure genetic continuity between generations - genetically similar
A strand of mRNA has 64 codons but the protein produced from it only has 63 amino acids. Suggest a reason why (1 mark)
one codon is a stop codon and they do not code for any amino acid
The genetic code can be described as degenerate but not ambiguous. Explain why (2 marks)
- most amino acids have more than one codon
- however any one triplet only codes for a single amino acid
Explain why the percentages of bases from the middle part of the chromosome and the end part are different (2 marks)
- Different genes;
- Have different (base) sequences
- (Pre-mRNA) transcribed from different DNA
Describe how two amino acids differ from one another (1 mark)
different R group
Explain why errors in DNA replication can be far more damaging than errors in transcription (2 marks)
- transcription usually only affects specific cells, are temporary and not inherited
- errors in DNA replication may be inherited and may have permanent effect on whole organism
A mutation was originally only found one one population in Central Asia. It is now found in many populations across Asia. Suggest how this spread occurred (1 mark)
migration
Suggest reasons why a non-resistant bacteria was able to grow in a culture containing bacteria (2 marks)
- mutation
- contamination w/ other bacteria
Two proteins have the same number and type of amino acids but different tertiary
structures.
Explain why. (2 marks)
1.Different sequence of amino acids
2. Forms ionic / hydrogen / disulfide bonds in different places;
