it is the chemical that all of the genetic material is made up of
DNA contains coded information
what is in the DNA determines the characteristics
DNA is found in the nucleus in long structures called chromosomes
Chromosomes normally come in pairs
DNA is a polymer
it is made up of two strands coiled together in the shape of a double helix
A gene is a small section of DNA found on a chromosome
each gene codes for a particular sequence of amino acids which are put together to make a specific protein
20 amino acids are used but they make up thousands of different proteins
genes tell cells in what order to put the amino acids together
determines what proteins the cell produces
determines what type of cell it is
genome is the entire set of genetic material in an organism
scientists have worked out the entire human genome
Human genome project 1990- team of scientists from all over the world worked together in tandem to map the human genome
The human genome project allowed scientists to
identify genes that are linked to different types of disease
knowing which genes are linked to which diseases helps develop effective treatments
trace migration to see where and when new populations split off
DNA strands are polymers made up of nucleotides
each nucleotide consists of a sugar, a phosphate, a base
each base links to a base on the other strand of the helix (ATCG)
this is complementary base pairing
the order of bases in a gene decides
the order of amino acids in a protein
each amino acid is coded for by a sequence of three bases in a gene
the amino acids are joined together to make various proteins, depending on the order of the gene's bases
there are parts of the DNA that don't code for proteins, some non-coding DNA switches on and off so control whether or not a gene is expressed
proteins are made in the cell cytoplasm ribosomes
to make proteins, ribosomes use the code in the DNA, DNA is found in the nucleus and can't move out because it is too big
the code is transferred between the nucleus and ribosome using mRNA which acts as a messenger between the DNA and ribosome
the correct amino acids are brought to the ribosomes in the correct order by carrier molecules
when a chain of amino acids has been assembled it folds into a unique shape
this allows the protein to perform the task it is designed to do
enzymes-biological catalysts
hormones-carry messages around the body
structural proteins-physically strong
mutations are changes to the genetic code
mutations can occur spontaneously
the chance of mutations can be increased by exposure to certain substances or types of radiation
mutations change the sequence of the DNA bases in a gene which produces a different genetic variant
as a sequence of DNA bases code for the sequence of amino acids that make up a protein, mutations to a gene can lead to changes in the protein that it codes for
most mutations have little to no effect
some will change it to such a small extent that its function or appearance in unchanged
mutations can severely affect a protein, can change its shape which can change its function
if the shape of an enzymes active site is changed, it may not be able to bind to a substrate
structural proteins could lose their strength
if there is a mutation in non-coding DNA
it can alter how genes are expressed
there are different ways mutations can change the DNA base sequence
insertions
deletions
substitutions
insertions
insertions are when a new base is inserted into a DNA base sequence
an insertion changes the way the groups of three are read which can change the amino acid they code for
can change more than one amino acid as they have a knock on effect
deletions
deletions are when a random base is deleted from a sequence
they change the way that the base sequence is read and have knock on effects
substitutions
substitution mutations are when a random base in the DNA sequence is changed to a different base
sexual reproduction produces genetically different cells
sexual reproduction is where genetic information from two organisms is combined to produce offspring which are genetically different to either parent
the mother and father produce gametes via meiosis
each gamete contains 23 chromosomes
the egg and sperm fuse together to from a cell with 46 chromosomes
sexual reproduction
involves the fusion of female and male gametes
there are two parents so the offspring contains a mixture of their parent's genes
the mixture of genetic information creates variation
there is only one parent so offspring are genetically identical
happens by mitosis
new cell has exactly the same genetic information- it is a clone
bacteria/some plant/animals reproduce asexually
asexual reproduction
only one parent
no fusion of gametes no mixing of chromosomes and no genetic variation
the offspring are genetically identical to their parent
gametes are produces by meiosis
gametes have only one copy of chromosomes so when gamete fusion takes place, there is the right number of chromosomes
meiosis involves two cell divisions, in humans this only happens in reproductive organs
meiosis
before the cell divides, it duplicates genetic information + chromosomes arrange themselves into pairs- they line up in the centre of the cell. they are pulled apart so each cell has one copy of each chromosome some of the fathers and mothers go into each new cell
in the second division, the chromosomes line up again and get split apart Produces four gametes with a single set of chromosomes, each gamete is genetically different from the others as the chromosomes get all shuffled up during meiosis
after two gametes have fused during fertilisation, the new cell divides by mitosis to make a copy of itself
mitosis repeats many times to produce lots of new cells in an embryo
as an embryo develops, the cells start to differentiate into the different types of specialised cell that make up a whole organism
sexual reproduction VS asexual reproduction
mixture of chromosomes- variation which increases the likelihood of an organism surviving a change in the environment
individuals with characteristics that make them better adapted to the environment have better chances of survival and more likely to breed successfully and pass on characteristics- natural selection
selective breeding speeds up natural selection
asexual reproduction VS sexual reproduction
one parent
less energy
faster
produced in favourable conditions
some organisms can reproduce by both methods
malarial parasites
fungi
plants
malarial parasites
malaria is cause by a parasite that's spread by mosquitoes
when a mosquito carrying the parasite bites a human, the parasite can be transferred to the human
the parasite reproduces sexually when its in the mosquito and asexually in the human
fungi
release spores which can become new fungi when they land in a suitable place
asexually-produced spores are identical to the parent
sexually-produces spores introduce variation and are in response to an unfavourable change in the environment
plants
asexual reproduction can take place in many different ways- strawberry plants produce runners that grow horizontally on the surface of the soil away from a plant and at various points a new strawberry plant forms
bulbs- new bulbs can form and divide off- each can form an identical plant
there are 23 pairs of chromosomes
22 matched pairs control characteristics
the 23rd pair are XX or XY
these two chromosomes decide your sex
females have XX chromosomes
males have XY chromosomes
when making sperm, the X and Y chromosomes are drawn apart
this gives a 50% chance of the sperm cell getting either chromosome
what genes you inherit control what characteristic you develop
different genes control different characteristics, some are controlled by a single gene