genetic information, variation and relationships between organisms Flashcards
what is the difference between eukaryotic and prokaryotic DNA?
eukaryotic=
-DNA is linear
-DNA is longer
-associated with histone proteins
prokaryotic=
-DNA is circular
-DNA is shorter
-not associated with histone proteins
how does DNA turn into a chromosome?
- DNA combined with histone proteins
- DNA-histone complex is coiled
- coils fold to form loops
- loops coil and pack together to form chromosome
what is the locus?
-position of a gene on a chromosome
what is the nature of the genetic code?
- triplet code= 3 bases of DNA code for 1 amino acid
- degenerate code= most amino acids can be coded for by a number of triplets
- non overlapping= each base in the sequence is only read once
- universal= each triplet codes for the same amino acid in all organisms
what are stop codons?
-3 triplets
-signals end of sequence
what is splicing?
-removes introns and puts exons together
-turns pre-mRNA into mRNA
what are exons and introns?
exons=
-coding section of genetic material
introns=
-non coding section of genetic material
how many chains do DNA, mRNA and tRNA have?
DNA=
-2 strands
mRNA=
-1 strand
tRNA=
-1 strand
what is the shape of DNA, mRNA and tRNA?
DNA=
-double helix
mRNA=
-single helix
tRNA=
-clover leaf
what is the relative size of DNA, mRNA and tRNA?
DNA=
-biggest
mRNA=
-bigger than tRNA but smaller than DNA
tRNA=
-smallest
what are the bases of DNA, mRNA and tRNA?
DNA=
-adenine, thymine, cytosine, guanine
mRNA and tRNA=
-adenine, uracil, cytosine, guanine
what is the pentose sugar of DNA, mRNA and tRNA?
DNA=
-deoxyribose
mRNA and tRNA=
-ribose
what is the location of DNA, mRNA and tRNA?
DNA=
-nucleus
mRNA=
-nucleus but found throughout the cell
tRNA=
-nucleus but found throughout the cell
what is the quantity of DNA, mRNA and tRNA?
DNA=
-constant for all cells of a species
mRNA=
-varies from cell to cell
tRNA=
-varies from cell to cell
what is the stability of DNA, mRNA and tRNA?
DNA=
-very stable
mRNA=
-least stable
tRNA=
-more stable than mRNA, but less than DNA
what are the names for 3 bases of DNA, mRNA and tRNA?
DNA=
-triplet
mRNA=
-codon
tRNA=
-anti codon
what is transcription?
-1st stage of protein synthesis
-nucleus
-produce a strand of mRNA for the gene being transcribed
what is the 1st stage of protein synthesis? (transcription)
- DNA helicase acts on a specific section of DNA, breaking hydrogen bonds and causing the DNA to unwind
- RNA nucleotides line up against bases on the template strand (complimentary base pairing)
- RNA polymerase joins adjacent RNA nucleotides together using phosphodiester bonds, forming a strand of pre-mRNA
- as the RNA polymerase adds nucleotides to the developing strand, the DNA closes behind it
- when RNA polymerase reaches 3 bases that it recognises as a STOP codon, it will detach
- pre-mRNA is spliced to form mRNA which leaves the nucleus via a nuclear pore
what is translation?
-2nd stage of protein synthesis
-ribosome
-translates mRNA code into a protein (primary structure)
what is the 2nd stage of protein synthesis? (translation)
- ribosome attaches to the start codon on mRNA
- tRNA with an anti codon that is complimentary to the start codon moves to the ribosome and pairs with the codon
- a tRNA molecule with an anti codon complimentary to the second codon moves to the ribosome
- a peptide bond forms between the 2 amino acids, this is catalysed by an enzyme (peptide transferase) and also requires energy from ATP
- ribosome moves along to the 3rd codon. As it does this, the first tRNA molecule is released
- processes continue until a STOP codon is reached
what is a genome?
-complete set of genes in a cell
what is a proteome?
-full range of proteins produced from the genome
what is a mutation?
-change in the quantity or base sequence of the DNA of an organism
what is a gene mutation?
-change in the number or sequence of DNA nucleotides
what are the 2 types of gene mutation?
-substitution mutation
-deletion mutation
what is substitution mutation?
-one nucleotide replaced with another nucleotide that contains a different base
what is deletion mutation?
-when a nucleotide is lost from the sequence completely
what is an allele?
-alternative form of a gene
what happens when there is changes to one or more bases in the DNA?
-triplets could result in a change in the amino acid sequence
what is a chromosome mutation?
-change in the structure or number of whole chromosomes
-change in the number of whole set would lead to polyploidy
-change in the number of individual chromosomes would be known as non-disjunction, which can lead to downs syndrome
what is meiosis?
-produces 4 haploid daughter cells
-involved in gamete production
what is the process of meiosis?
- first division (meiosis 1)=
-homologous chromosomes pair up and their chromatids wrap around each other
-by the end of this division the homologous pairs have separated, with one chromosome from each pair going into one of the two daughter cells - second division (meiosis 2)=
-chromatids move apart
-by the end of this division, 4 cells have usually formed
what two ways does meiosis bring about genetic variation?
-independent segregation
-genetic recombination by crossing over
what is the process of genetic recombination by crossing over?
- chromatids of each pair become twisted
- during this twisting process, tensions are created and portions of the chromatids break off
- these broken portions might then re-join with the chromatids of its homologous partner
- usually it is the equivalent portions of homologous chromosomes that are exchanged
- in this way new genetic combinations of maternal and paternal alleles are produced
what is the process of independent segregation?
- each chromosome lines up alongside its homologous partner
- these pairs arrange themselves in the line at random
- one of each pair will pass to each daughter cell
- since the pairs are lined up at random, the combination of chromosomes of maternal and paternal origin that go into the daughter cell is a matter of chance in meiosis 1
what are the possible chromosome combinations (calculations)?
2 to the power of n, where n is the number of homologous chromosome pairs
-determines the possible number of combinations of chromosomes for each daughter cell
(2 to the power of n) squared, where n is the number of homologous chromosome pairs
-determines the possible number of combinations of chromosomes for each daughter cell coming from random pairings of male and female gametes
what is genetic diversity?
-total number of different alleles in a population
-the greater number of different alleles in a population, the greater the genetic diversity
-genetic diversity is a factor that enables natural selection to occur
what is a gene pool?
-all alleles for all genes for all individuals in a population
what is allelic frequency?
-the number of times an allele occurs in a gene pool
what is natural selection in terms of allele frequency?
- random mutation of alleles within gene pool and may result in new allele
- this new allele may give its possessor an advantage over other individuals in the population
- these individuals will be better adapted and therefore more likely to survive
- they are more likely to obtain available resources, so grow more rapidly and live longer
- they will have a better chance of successfully breeding and producing more offspring
- this breeding will pass on their advantageous alleles to the next generation
- over many generations, the number of individuals with the new advantageous allele will increase at the expense of the individuals with the less advantageous allele
what are the two types of selection?
-directional
-stabilising
what is directional selection?
-favours the individuals at the extremes (either left or right of the mean in the population)
-changes the characteristics of the population
what is stabilising selection?
-favours the average individual
-keeps the characteristics of the population
what are the three types of natural selection adaptations?
anatomical=
-shorter ears and thicker fur in arctic foxes
physiological=
-oxidising of fat rather than carbs in kangaroo rats to produce additional water in dry conditions
behavioural=
-autumn migration of swallows from the UK to Africa to avoid food shortages in winter
