Protein Synthesis And Selection Flashcards
What are the differences between eukaryotic DNA and prokaryotic DNA?
E= linear
P= circular
E= associated with histone proteins
P= not associated with histone proteins
E= contains introns
P= does not contain introns
DNA vs mRNA
- DNA is double stranded whereas mRNA is single stranded
- DNA is longer whereas mRNA is shorter
- Thymine in DNA whereas replaced with uracil in mRNA
- Deoxyriboxe in DNA whereas ribose in RNA
- DNA has hydrogen bonds whereas mRNA doesn’t have hydrogen bonds
- DNA has introns whereas mRNA doesn’t have introns
Describe transcription
- DNA helicase breaks hydrogen bonds causing strands to separate
- Only one DNA strand acts as a template
- RNA nucleotides are attracted to exposed bases
- According to base pairing rule - Adenine to uracil and cytosine to guanine
- RNA polymerase joins nucleotides together forming phosphodiester bonds through condensation reactions
- Pre-mRNA spliced to remove introns (eukaryotes)
Describe translation
- mRNA binds to ribosome
- Ribosome identifies start codon
- 2 binding sites
- tRNA with complimentary anticodon to codon on mRNA binds to codon
- Amino acids joined by peptide bonds using energy from ATP
- tRNA released as ribosome moves along mRNA
- Ribosome reaches stop codon and releases polypeptide
What does the genetic code being universal mean?
The same 3 bases on mRNA / DNA code for the same amino acids in all organisms
What does the genetic code being non-overlapping mean?
Each base is only part of 1 triplet
What does the genetic code being degenerate mean ?
More than one triplet codes for an amino acid
Define gene mutation
A change to the base sequence of a gene resulting in the formation of a new allele
Name 3 mutagenic agents
- High energy ionising radiation
- DNA reactive chemicals
- Biological agents
Describe the process of natural selection
- Variation exists within a population due to mutation
- Better adapted individuals more likely to survive and reproduce ( differential reproductive succes)
- These organisms are more likely to pass on their alleles
- Those which are less well adapted fail to survive and reproduce
- Leads to change in allelic frequency
- Occurs over a long period of time
Describe stabilising selection
- Selection against both extremes
- Only mean phenotype will have reproductive success
- Alleles for mean phenotype are passed on to future generations in greater numbers
- Over time frequency of mean alleles coding for mean phenotype increases
- Alleles coding for both extreme phenotypes decreases
Describe directional selection
- Selection for only one extreme
- Individuals with advantageous allele have increased reproductive succes
- Alleles for one extreme are passed on to future generations in greater numbers
- Over time frequency of this extreme allele increases
- Alleles coding for the other extreme phenotype decreases
