Topic 4: Genetic information, variation and relationships between organisms Flashcards
What is a gene
A section of DNA that codes for the amino acid sequence of a polypeptide and functional RNA
What is an allele
A different form of the same gene
what is the locus
the location of a particular gene on a chromosome
describe chromosomes
this is how DNA is stored. humans have 23 pairs
what is a homologous pair
pair of chromosomes that have the same genes but might have different alleles
how is DNA stored in eukaryotes
as chromosomes in the nucleus. they are linear and get tightly wound around histone proteins to create nucleosomes.
how is DNA stored in prokaryotes
short and circular supercoiled to fit into the cell
differences between DNA in eukaryotes and prokaryotes
E- linear
P-circular
E- wrapped around histones
P-not protein bound
what organelles contain their own DNA
mitochondria and chloroplast because they have central reactions. photosynthesis and respiration
how is DNA in the mitochondria and chloroplast similar to prokaryotic DNA
DNA is short and circular
Not histone bound
What are three features of genetic code? Explain them
Degenerate- each amino acid is coded for by more than one codon
Universal- the same triplet base codes for the same amino acid in all organisms
non overlapping- each base in a gene is only part of one triplet of bases that codes for one amino acids. each codon is read as a discrete unit
how many amino acids are there
20
what are the four DNA bases
Adenine
Thymine
Cytosine
Guanine
what is the advantage of a degenerate code
if a substitution mutation occurs, the triplet base may be different but it will still code for the same amino acid.
advantage of a universal code
allows genetic engineering to occur e.g production of insulin
advantage of a non overlapping code
if a point mutation occurs, it will only affect one codon so just one amino acid
what is an intron
sections of DNA that do not code for amino acids. not found in mRNA or prokaryotic DNA
what is an exon
section of DNA that codes for an amino acid
genome vs proteome
the genome is an organisms complete set of DNA in one cell while the proteome is the full range of proteins in one cell
The genome should never change but the proteome changes quite often
what is the structure of RNA
polymer of a nucleotide formed of a ribose, a nitrogenous base and a phosphate group
what is the function of RNA
to copy and transfer genetic information
combines with proteins to create ribosomes
what are the types of RNA
messenger
transfer
ribosomal
what are purine bases
Adenine and Guanine. They have double ring structures
what are pyrimidines
Thymine, Uracil, Cytosine. single ring structures
what bond joins nucleotides
phosphodiester bonds
what are the stages of protein synthesis
transcription and translation
describe the structure of mRNA
long single strand
base sequence is complementary to DNA
each codon set match a codon on DNA and tRNA
describe the structure of tRNA
clover leaf shape
has an anti codon on the opposite end specific to the amino avid that it attaches to
what happens during transcription
a molecule of mRNA is made in the nucleus
what happens during translation
amino acids join together to form a polypeptide chain
explain the process of transcription
- DNA helix unwinds to expose the bases to act as a template
- One chain is the template.
- This is catalysed by DNA helicase which breaks the H bonds
- free mrna nucleotides align opposite complementary bases
- RNA polymerase joins rna nucleotides to create a new polymer chain
explain the process of translation
- mRNA attaches to a ribosome and tRNA collects amino acids from the cytoplasm to the ribosome.
- tRNA is a single stranded molecule with a binding site at one end so it can only carry one type of amino acid, and an anti codon.
- tRNA attaches itself to mRNA by complementary base pairing
- The amino acids attached to two tRNA molecules join by a peptide bond and then tRNA molecules detach themselves from the amino acids, leaving them behind
what is a mutation
any change to the base sequence of DNA
what is a substitutIon mutation
this is when one nucleotide in the DNA sequence is replaced by another. A substitution may not always be harmful as the substituted nucleotide may code in that triplet for the same amino acid.
what is a deletion (frameshift) mutation
a deletion event is when a nucleotide in the DNA sequence is lost. The loss of a single nucleotide can have a significant impact as it leads to a frame shift, resulting in completely different amino acids being coded for.
what are two types of chromosome mutations
polyploidy and non-disjunction
what is a polyploidy mutation
changes in the whole set of chromosomes. when organisms ,have 3 or more sets of chromosomes rather than 2.
what is a non disjunction mutation.
When chromosomes fail to separate properly during anaphase of meiosis.
what are two types of cell division and the main difference
mitosis produces two identical daughter cells and meiosis produces 4 genetically different cells
what happens in meiosis 1
homologous chromosomes pair up and chromatids wrap around each other.chromatids may exchange by crossing over.The cell then divides whereby each daughter cell contains one chromosome from each homologous pair.
what happens in meiosis 2
chromatids. move apart producing 4 daughter cells
how is genetic variation achieved in meiosis
-independent segregation of homologous chromosomes (there are various combinations of chromosome arrangement. During meiosis 1 homologous chromosomes line up in pairs, the arrangement of these pairs is random, meaning that the division into the daughter cells is also random.)
-crossing over between homologous chromosomes When pairs of chromosomes line up they can exchange some of their genetic material. Crossing over occurs when one chromosome may swap
places with the same part of its homologous pair leading to a different combination of
alleles on the gene.
what is genetic diversity
number of different alleles of genes in a population.
what is a population
a group of individuals of the same species that live in the same place and are able to breed with one another.
what isnatural selection
process in which fitter individuals who are betted adapted to the environment survive and pass on the advantageous genes to future generations
what is evolution
Evolution is the process by which the frequency of alleles in a gene pool changes over time as
a result of natural selection
what are the types of selection
directional and stabilising
what is directional selection
when the advantageous allele is coding for extreme traits
what is stabilising selection
individuals with alleles towards the middle range are more likely to survive and reproduce
two organisms belong to a species if…
If they are able to produce fertile offspring
list the hierarchy of taxa
Domain Kingdom Phylum Class Order Family Genus Species
what is species richness
a measure of the number of different species in a community.
what is biodiversity
the variety of living organisms in an area
what reduces biodiversity
monoculture
pesticides and herbicides
woodland clearance
hedgerow removal
