Unit 4

• name and describe the three features of the genetic code

  degenerate - multiple triplets codes for the same amino acid

  universal - the same triplet will code for the same amino acid in all organisms

  non-overlapping - each base is only a part of one triplet
• describe transcription

  hydrogen bonds between bases are broken

  only one strand acts as a template

  complementary base pairing between DNA bases and free RNA nucleotides

  RNA polymerase join adjacent nucleotides by condensation forming phosphodiester bonds

  pre-mRNA is spliced to remove introns
• describe translation

  mRNA attaches to ribosomes

  complementary base pairing between tRNA anticodons and mRNA codons

  tRNA brings a specific amino acid

  ATP is used to join amino acids by condensation

  peptide bonds form

  tRNA released

  ribosome moves along mRNA to form polypeptide
• what is a mutation

  a change in the DNA base sequence
• define the term mutagenic agent

  something that increases the rate of mutation
• describe crossing over

  homologous chromosomes form a bivalent

  form chiasmata

  alleles are exchanged between non sister chromatids

  producing new allele combinations - recombinants
• compare and contrast the DNA in eukaryotic and prokaryotic cells

  contrast:

  eukaryotic DNA is longer

  eukaryotic DNA has introns prokaryotic doesn't

  eukaryotic DNA is linear , prokaryotic DNA is circular

  eukaryotic DNA is associated with histones

  compare:

  identical nucleotide structure

  nucleotides joined by phosphodiester bonds
• State the differences between mRNA and tRNA

  mRNA is located in the nucleus whereas tRNA is located cytoplasm

  mRNA is shorter

  mRNA has codons whereas tRNA has anticodons

  mRNA is a straight chain whereas tRNA is a clover shape
• describe what occurs in meiosis 1

  prophase 1:

  nuclear envelope breaks down

  chromosomes condense

  chromosomes are arranged in homologous pairs - bivalents

  metaphase 1:

  bivalents line up at the equator

  spindle fibre attach to centromeres and opposite poles of the cell

  anaphase 1:

  centromeres do not divide

  homologous chromosomes are separated as microtubules pull whole chromosomes to opposite poles

  telophase 1:

  nuclear envelope forms around the two groups of chromosomes
• describe the process of natural selection

  random mutation

  introduces genetic variation

  gives rise to new advantageous allele

  reproductive selective advantage

  reproduce - allele is passed to fertile offspring

  increases allele frequency

  increases survival
• genetic diversity within or between species can be investigated by comparing

  DNA base sequence

  mRNA base sequence

  amino acid sequence of proteins encoded by DNA and mRNA
• limitations of comparing observable characteristics

  characteristic could be polygenic or could be influenced by the environment
• describe the structure of a chromosome

  two sister chromatids

  made with chromatin

  containing genes

  chromatids are attached at the centromere
• Explain why it is more useful to calculate the index of diversity then species richness?

  index of diversity measures abundance + the population size of each species

  some species may be in low or high numbers
• What experiment would you do to determine if organisms where from the same species?

  Breed - Where if fertile offspring is produced they are from same species.
• What does it mean when organisms have the same genus?

  They have the same common ancestor.
• What is a Hierarchy

  Smaller groups arranged within larger groups Where there is no overlap between the groups.
• What is Evolution

  Change in allele frequency over many years.
• What is a proteome?

  Organisms full range of proteins which the cell is able to produce
• What is a genome?

  An organisms complete set of genes in a cell. Only change due to mutation.
• What is a stop codon?

  The final 3 bases of every gene that stop translation.
• What is a start codon?

  The first 3 bases at the start of every gene that initiate translation.
• What is a locus?

  The exact position where the gene is found on a chromosome.
• What are introns?

  Non-coding regions of DNA which are found in eukaryotic cells but not prokaryotic.
• What is an exon?

  Coding region of DNA that code for an amino acid
• What does standard deviation tell us?

  How far the values are spread above and below the mean
• Why is it better to compare the mRNA sequence of different organisms than the DNA sequence

  mRNA is shorter than DNA

  mRNA has no introns

  theres many mRNA in a cell whereas each cell only has two copies of each gene
• How does conservation of biodiversity benefits farmers

  More pollination

  cheaper as less pesticides have to be bought and applied
• What is the disadvantage of using chemical fertilisers

  they are water soluble so leach out of the soil into rivers and lakes causing eutrophication
• For representative samples…

  random sampling in uniform areas to avoid selection bias

  line transects if area change over distance

  use large sample size
• describe eukaryotic DNA

  DNA is found in the nucleus surrounded by nuclear envelope

  DNA double helix is surrounded by histone proteins to from nucleosomes

  nucleosomes coil up to form chromatin

  chromatin is organised into chromosomes

  DNA contains non-coding bases sequences called introns and coding sequences called exons
• what is the locus/loci

  the locus is the fixed position of a genes on a chromosome
• describe mRNA

  short

  single stranded

  helical

  polynucleotide

  made in nucleus during transcription

  carries genetic code into cytoplasm for translation

  3 bases = codon

  chemically unstable -broken down within days

  variable lengths depending on the length of the gene it was transcribed from
• describe tRNA

  single stranded

  folded into a clover shape

  made in nucleus

  3 bases = anticodon

  has specific amino acid binding site

  carries amino acids to ribosomes

  more stable then mRNA less stable than DNA
• what is the effect of a cell having an odd number of chromosomes

  bivalents cannot form

  fertile gametes cannot be produced
• define species

  a groups of similar organisms that are able to successfully reproduce to give fertile offspring
• what is analogy

  when species have similar characteristics with the same function but have different evolutionary history
• Explain why DNA replication is semi-conservative and its importance within the body

  each new DNA molecules contains one old , original strand and one new strand

  ensures genetic continuity
• function of mRNA

  once formed in transcription

  leaves the nucleus via the nuclear pores

  enters the cytoplasm

  associates with ribosomes and acts as a template for proteinsynthesis
• tRNA anticodons are complementary to mRNA codons

  mRNA codons are complementary to DNA triplet