Exam question topic four

• Describe how a gene is a code for the production of a polypeptide (3£

  1. Specific base sequence
  2. Read in triplets
  3. Determining the sequence of amino acid in the primary structure
• Compare and contrast dna in eukaryotic cells with dna in prokaryotic cells

  1. Nucleotide structure identical
  2. Both have nucleotides joined to each other by phosphodiester bonds
  3. DNA in mitochondria and chloroplast similar to dna in prokaryotic cells
  4. Eukaryotic dna is longer
  5. DNA in eukaryotic has intron regions but no introns in prokaryotic
  6. Eukaryotic is linear but prokaryotic is circular
  7. DNA in eukaryotic cells is associated with Justine proteins but isn’t in prokaryotic
• Describe how mRNA is produced from an exposed template strand don’t include helicase or splicing (3)

  1. Free rna nucleotides form complementary base pairs
  2. Phosphodiester bonds
  3. Action of rna polymerase
• In a eukaryotic cell the structure of mRNA used in translation is different from pre mRNA produced by transcription. Describe and explain difference in the structure of the mRNA molecules (2)

  1. mRNA doesn’t have introns
  2. Due to splicing
• Describe how one amino acid is added to a polypeptide that’s being formed at a ribosome during translation. (2)

  1. tRNA brings a specific amino acid to the ribosome
  2. Anticodon on tRNA binds to the codon on mRNA
  3. Amino acids are joined by condensation reaction using atp forming peptide bond
• A particular gene is 562 base pairs long but resulting mRNA is 441 nycleotides long explain why

  mRNA is only exons / dna contains introns
• Explain how the substance stops protein synthesis

  1. Binds to codon on mRNA so trna Can’t fit
  2. Amino acids not delivered / joined

  
• Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide give two reasons why

  1. Occurs in the intron regions
  2. genetic codes / triplets degenerate so amino acid sequence remains the same
• Describe how mRNA is formed by transcription in eukaryotes (5)

  1. DNA helicase breaks hydrogen bonds between complementary base pairs
  2. Only one strand acts like a template
  3. Free RNA nucleotides align to exposed bases by complementary base pairs
  4. In rna uracil used in the place of thymine
  5. RNA polymerase joins adjacent rna nucleotides
  6. By forming phosphodiester bonds
  7. pre mRNA is spliced by enzymes to form mRNA
• Suggest one advantage of showing genetic codes as base sequence on mRNA rather than dna triplets

  ribsone assemble polypeptide using mRNA codons
• During which part of the cell cycle are gene mutations most likely to occur and suggest an explanation for your answer (2)

  1. S phase
  2. DNA’s replicated
• Explain why the number of chromosomes is halved during meiosis

  Homologous chromosomes are separated during meiosis one
• Other than mutations and meiosis how does genetic variation in a species increase

  1. Random fusion of gametes
  2. New allele combination
• Importance of meoisis

  1. Two division create haploid gamete’s
  2. It maintains the chromosome number between generations as offspring is diploid
  3. Independent segregation crossing over creates genetic variation
• Describe. How mutation the number of chromosomes arise

  1. Spontaneously by chromosome non-disjunction during meiosis
  2. Homologous chromosomes or sister chromatic fail to separate during meiosis
  3. Some gamete’s have extra copy of chromosome and some have none
• Describe and explain appearance of chromosome in cell x (3)

  Chromosome appears as two sister chromatids; held together at centromere ; dna has replicated

  
• Describe what happened in division one (2)

  Homologous pair Of chromosomes is separated ; one of each into the daughter cell
• Identify one event during meiosis two but not one

  Separation of sister chromatids or division of centromere
• Describe and explain the processes that occur during meiosis that increase genetic

  variation. (5)

  1. homologous chromosomes pair up
  2. Independent segregation
  3. Maternal and paternal chromosomes are reshuffled into any combination
  4. Crossing over leads to exchange of parts of non sister chromatids between homologous chromosomes
  5. Both create new combinations of alleles
• During meiosis one chromosome from each homologous pair goes to each of the cells produced explain why this is more important (2)

  1. To get haploid number of chromosomes
  2. Each cell gets one copy of each chromosome / maintains chromosome number
  3. Results in independent segregation
• Describe how crossing over occurs during meiosis

  1. Pair of homologous chromosome twist around each other
  2. Chromatids snap of and rejoin chromatid on a sister chromosome
• Describe how polypeptide produced during translation

  mRNA attaches) to ribosome

  2. (tRNA) anticodons (bind to) complementary

  (mRNA) codons;

  3. tRNA brings a specific amino acid;

  4. Amino acids join by peptide bonds;

  5. (Amino acids join together) with the use of ATP;

  6. tRNA released (after amino acid joined to

  polypeptide);

  7. The ribosome moves along the mRNA to form the

  polypeptide;
• explain the importance of meiosis in the life-cycle of organisms which reproduce sexually (3)

  1. Meiosis produced haploid cells / halves the chromosomes number
  2. When gametes fuse diploid numbers restored / maintains chromosome from one generation to the next
  3. Allows genetic variation / introduced independent assortment / crossing over
• What is the biological importance of reducing the chromosome number when the cell divides by meiosis (2)

  1. After fertilisation/ gametes fuse
  2. It restores the diploid number / original number / doesn’t double chromosome number
• Term used to describe the pair of homologous chromosomes

  Bivalent

  
• Give processes other than crossing over which results in genetic variation and explain how each process contributes to genetic variation (6)

  1. Mutation
  2. Different allele formed / genes deleted / sequence of genes change
  3. Independent segregation
  4. Produces new combination of allele
  5. Random fusion of gametes
  6. New combination of alleles
• Define exon

  Base / nucleotide sequence coding for a polypeptide / primary structure
• Define non coding base sequence and describe Where the non coding multiple repeats are positioned (2)

  1. DNA that doesn’t code for proteins / polypeptides / sequence of amino acids
  2. Positioned between genes
• Define mutagenic agent

  Factors that increases the rate of mutation
• Mutation in the number of chromosomes in S.townsendii chromosomes 61 produced new species s Angelica with chromosomes 122 name the type of mutation changing the number of chromosomes to produce new species and explain your answer (3)

  1. Non disjunction
  2. In meiosis
  3. Chromosomes not separated / all chromosomes stay in one cell
• female trout are treated to produce diploid egg cells. offspring produced from this farmed trout are sterile suggest and explain why (2)

  1. Contains three copies of each chromosome
  2. Can’t form homologous pairs
  3. Is no meiosis
• Define gene mutation and explain how a gene mutation can have no effect on an individual and positive effect on an individual. (4)

  1. Change in base sequence of dna
  2. Results in formation of new alleles
  3. No affect as genetic coded degenerate so amino acid sequence doesn’t change / mutations in a intron
  4. Doesn’t change amino acid so no effect on tertiary structure
  5. New alleles recessive so doesn’t affect phenotype
  6. Positive effect results in change in polypeptide that positively changes the properties of protein
  7. May result in increases reproductive success / survival chance
• Describe the process of crossing over and explain how it increases genetic diversity (4)

  1. homologous chromosomes pair up to form a bivalent
  2. Forms chiasmata
  3. Equal length of non sister chromatids exchanged
  4. Creates new combinations of alleles
• explain why all cells of the body cells will have this mutation of an extra chromosome 13

  1. Mutations in gamete that forms the zygote
  2. all cells derived from zygote by mitosis
  3. Or
  4. All cells derived from a sinhle cell by mitosis
  5. Mitosis produced genetically identical cells
• What’s terms used to describe naming of organisms

  Bionomial
• The scientist studiedindividuals from each species within the five individuals of species N they found a percentage similarity of 66% use table to evaluate how this information affects the validity of the phylogenetic tree

  1. Supported as more similar than with any other species
  2. Not supported as theirs high intraspecific variation in species n compared to variation between n and c
  3. Small sample / only five people

  
• What do these classifications suggest about the evolutionary relationships

  between these species of snake?

  1. X suggests that mackloti and olivaceous have a more common ancestor
  2. Y suggests that papuana and mackloti have a more common ancestor

  
• There are many different species of field mouse in Europe. Using a phyloganetic classificaton, all of these species have fiames that start with Apodemus.

  What information does this give about field mice?

  1. Same genus
  2. Same evolutionary origin / evolved from common ancestor
• Describe how breeding experiments could determine whether the two populations of mice are from the same species

  1. Breed the two mice together
  2. Same species produce fertile offspring
• Suggest a source of dna for an otter alive before hunting started

  1. Bone / skin /preserved remains