Genetic information, variation and relationships between organisms Flashcards
DNA in eukaryotes vs. prokaryotes
Eukaryotic DNA: long, linear, associated with histones, tightly coiled into chromosomes
Prokaryotic DNA: short, circular, not associated with proteins/histones
DNA in mitochondria and chloroplasts
Short, circular, not associated with proteins/histones
What are genes
A sequence of DNA bases that codes for the amino acid sequence of a polypeptide, or. a functional RNA
Genes occupy fixed positions called locus
Features of the genetic code
-Sequence of DNA triplets (or mRNA codons) codes for a sequence of amino acids
-Universal; The same specific DNA base triplets code for the same amino acids in all living organisms
-Non overlapping; Discrete, each base can only be used once and in only one triplet
-Degenerate; The same amino acids can be coded for by more than one base triplet
Where in eukaryotes does DNA not code for polypeptides
-Between genes: non coding multiple repeats
-Within genes: only exons code for amino acid sequence, not introns
Genome
Complete set of genes in a cell, incl. mitochondria/chloroplast
Proteome
Full range of proteins that a cell/genome is able to produce
Alleles
Different version of the same gene
Homologous pair of chromosomes
Same size chromosomes with the same genes, but different alleles
mRNA function and structure
-made by transcription in the nucleus
-acts as template in the cytoplasm
-sequence of bases on RNA determines sequence of amino acids in polypeptide chain
-straight chain molecule
-sequence of bases on RNA determined by sequence of bases on DNA
-triplet code=codon
-chemically unstable so breaks down after a few days
tRNA structure and function
-Carries an amino acid on amino acid binding site
-anticodon=3 bases, complementary ti mRNA codon
-each tRNA specific to one amino acid, in relation to its anticodon
-single polynucleotide strand
-3 leaf clover shaped
-held together by H bonds
Compare and contract structure of mRNA and tRNA
compare: both singles polynucleotide strand
contrast:mRNA straight, tRNA folded into clover shaped. mRNA longer, tRNA shorter. mRNA contains no paired bases or H bonds, tRNA has paired bases and H bonds
Transcription
-In the nucleus, DNA double helix is unzipped by helicase
-H bonds breaks
-RNA nucleotides align next to complementary bases on the template strand, forming temp H bonds (uracil replaces thymine)
-RNA polymerase joins adjacent nucleotides, condensation reaction, forming phosphodiester bonds
-Pre-mRNA/mRNA detaches from DNA when RNA polymerase reaches stop codon
-mRNA leads nucleus via nuclear pores
Post transcription
In eukaryotes, pre-mRNA is spliced; introns removed and exons spliced together (in different combos for different proteins)
Translation
-sequence of mRNA codons determines sequence of amino acids
-tRNAS carry specific amino acids, in relation to their anticodon
How is one amino acid added to a polypeptide that is being
formed at a ribosome during translation.
-tRNA brings specific amino acid (to ribosome
-anticodon (on tRNA) binds to codon (on mRNA);
-amino acids join by condensation reaction and form peptide bond (using ATP)
How is a polypeptide is formed by translation of mRNA
-mRNA attaches to ribosomes
-tRNA anticodons bind to complementary mRNA codons;
-tRNA brings a specific amino acid;
-amino acids join by peptide bonds;
-amino acids join together with the use of ATP
-tRNA released after amino acid joined to polypeptide
-the ribosome moves along the mRNA to next codon until stop codon to form the polypeptide;
Role of ATP in translation
-hydrolyses ATP, to release energy for;
-bond between amino acid and corresponding tRNA molecule
-peptide bond between amino acids
Role of tRNA in translation
-attaches to and transports specific amino acid, in relation to anticodon
-anticodon complimentary base pairs with mRNA codons, forming H bonds
-2 tRNAs bring amino acids, forming peptide bonds
Role of ribosomes in translation
-allows tRNA with anticodons to bind
-catalyses formation of peptide bonds between amino acid
-moves along mRNA to next codon
-mRNA binds to ribosomes
What is gene mutation
-A change in base sequence of DNA on chromosomes
-Can arise randomly during interphase
-May involve base deletion/substitution
Production of non functional protein
-Change in base sequence of DNA
-Changes sequence of codons on mRNA
-Changes sequence of amino acids in the primary structure of the polypeptide
-Changes position of Hydrogen/ionic/disulfide bonds in tertiary structure of protein
-Changes tertiary structure (and active site if enzyme, so substrate can no longer bind and no E-S complex)
Base deletion
-One nucleotide removed from DNA sequence
-Changes codon sequence from point of mutation
-Changes sequence of amino acids in primary structure of polypeptide
-Changes position of Hydrogen/ionic/disulfide bonds in tertiary structure of protein
-Changes tertiary structure
Base substitution
-Nucleotide in DNA replaced with another nucleotide
-change in one base, changes only one triplet
1. Changes one code and one amino acid, sequences of amino acids in primary structure of polypeptide changes
2. Degenerate nature of genetic code, new triplet may still code for same amino acids so sequence of amino acids in primary structure remains the same
Mutagenic agents
Increase rate of gene mutation e.g UV light/alpha particles
Pre meiosis
-DNA replicates so there are two copies of each chromosome, called sister chromatids, joined by centromeres
Meiosis I
Homologous pairs seperate
-Chromosomes arrange into homologous pairs
-Crossing over and independent segregation can occur
Meiosis II
Chromatids seperate
-Creates 4 haploid cells that are genetically varies
Crossing over
-Alleles exchange between chromosomes
-Creates new combos of maternal and paternal alleles on chromosomes
Independent segregation
-Random alignment of homologous pairs of chromosomes at equator, random which chromosome from each pair goes to each daughter cell
-Creates different combos of maternal and paternal chromosomes and alleles in daughter cells
Random fertilisation
Two gametes fuse to form a zygote
Importance of meiosis
-2x divisions- creates haploid gametes
-Diploid number restored at fertilisation
-Maintains chromosome number from gen to gen
-Independent segregation and crossing over creates genetic variation
What happens if there are mutations in chromosome numbers
-Homologous chromosomes fail to separate during meiosis I
-Sister chromatids fail to separate during meiosis II
-One gamete has extra copy of its chromosomes and the other has none
-Fertilisation: Zygote has one fewer (dies), other has one extra (survives)
-Causes genetic disease
Calculation: number of possible combos of chromosomes in daughter cells after meiosis (no crossing over)
2^n
-n=number of pairs of homologous chromosomes
Calculation: number of combos of chromosomes following random fertilisation of two gametes
2^2n
-n=number of pairs of homologous chromosomes
Mitosis v. Meiosis
Mitosis produces diploid cells, meiosis produces haploid cells
Two divisions in meiosis, one division in mitosis only sister chromatids separate
Daughter cells genetically identical to each other in mitosis, genetically varied in meiosis
Meiosis 4 daughter cells, mitosis 2 daughter cells
No crossing over in mitosis, crossing over in meiosis
What is genetic diversity
-Number of different alleles of a gene in a population
-Population- group of interbreeding individuals of the same species
Evolution
Change in allele frequency, over many gens in a population
Natural Selection Principle (MARIA)
Mutation- random gene mutation results in new alleles of a gene
Advantage- in certain environments, the new allele might benefit its possessor, organism has selective advantage
Reproductive success- possessors are more likely to survive and have increased reproductive success
Inheritance- advantageous allele is inherited by offspring
Allele frequency- over many gens, advantageous allele increases in frequency in the population
Directional selection
occurs in organisms with extreme variation of a trait, e.g. bacteria with high resistance to an antibiotic
-change in environment, e.g. antibiotic introduced
-increases frequency of organisms with the extreme trait
-normal distribution of curve shifts towards extreme trait
Stabilising selection
occurs in organisms with average variation of a trait, e.g babies with avg weight
-stable environment
-both extremes of phenotypes are less likely to survive and reproduce
-increased frequency of organisms with avg trait
-normal distribution curve simila, less variation
How are fertile offspring produced
Two organisms within same species mate to produce fertile offspring. If they don’t belong to same species, they’re offspring will have an odd number of chromosomes so can’t undergo meiosis to produce sex cells
Role of courtship behaviour in species recognition
-indication of sexual maturity
-recognition of opposite sex
-stimulates release of gametes
-establishes a pair bond to raise young
-synchronises mating, max probability that sperm fertilises ovum
Hierarchy?
Smaller groups placed within larger groups, no overlaps between each group (taxon)
Taxonomic hierarchy
Dear King Philip Came Over For Good Soup
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Advantage of binomial consisting of Genus and species
universal; no confusion as many organisms have more than one common name
How does immunology clarify evolutionary relationships
DNA determines mRNA, determines sequence of amino acids in a polypeptide
Tertiary structure of proteins tells us about sequence of DNA, if same antibody binds to a specific antigen then there is a close relation
How does gene sequencing clarify evolutionary relationships
Compare order of base sequence of whole genome of different species’
-higher % match, more closely related
Habitat?
Place where an organism lives
Biodiversity?
Variety of living organisms
-species diversity
-genetic diversity
-ecosystem diversity
Community?
All the populations of different species in a habitat
Species richness
-number of different species in a community
Index of diversity
N(N-1)/Σ n(n-1)
N- total number of organisms of all species present
n- total number of organisms of each individual species
Σ- sum of
*greater species richness=higher index of diversity
Why is index of diversity better measure than species richness
-IoD measures the number of individuals in a species, as well as measuring the number of species so it takes account for the fact that some spices may be present in low/high numbers
Examples of farming techniques that reduce biodiversity
-Removal of woodland and hedgerows
-Monoculture e.g. growing one type of crop
-Use of herbicides
Reduces variety of plants, so fewer habitats, less variety of food sources
-Use of pesticides to kill pests
Predator population of pest decreases
Balance between conservation and farming
-Conservation required to increase biodiversity, however on farms the yields are reduced and farmers make less bank :(
for e.g. reducing land area for crop growth, increasing competition, increasing pest population
-To make sure farmers are making bank, grants are offered by the EU
Conservation techniques that can increase biodiversity without lowering yields
-Reduce use of pesticides
-Growing different crops in the same area
-Using crop rotation of Nitrogen fixing crops instead of fertilisers
-Field margins and hedgerows
What is variation and how can it arise
Differences in characteristics between individuals
Intra- same
inter-different
Result of genetic factors, environmental factors- or both!
Continuous variation
No distinct categories
Data mostly quantitative
Controlled by ,any genes
Strongly influenced by environment
Discontinuous variation
Distinct, discrete categories
Data tends to be qualitative
Controlled by single/few genes
Unaffected by environment
`How is genetic diversity determined
Frequency of observable characteristics
-Indicates genetic diversity because its based on the fact that different alleles determine different characteristics
Base sequence of DNA and mRNA
Amino acid sequence of the proteins encoded by DNA and mRNA
Limitations of estimates of genetic diversity made by observing characteristics
-Many characteristics coded for by more than one gene, difficult to distinguish one from another
-Characteristics could be modified by the environment so differences may be a result of environmental conditions rather than alleles
