Paper 2 TOPICS 2022 Flashcards
where are chromosomes found?
- in the NUCLEUS.
- it contains your genetic material in the form of chromosomes.
what is a chromosome?
long lengths of DNA coiled up. genes are located on here.
what are genes and where are they located?
- a gene is a section of a molecule of DNA that codes for a specific protein.
- located on a chromosome
what is DNA?
a long list of instructions on how to put an organism together and make it work.
what is the genome?
the entire DNA of an organism.
what is each separate gene in a DNA molecule?
each separate gene in a DNA molecule is a chemical instruction that codes for (says how to make) a particular protein.
why are proteins in the body important?
- they control most processes in the body
- they also determine inherited characteristics e.g. eye colour, blood type.
how do genes control our inherited characteristics?
by controlling the production of proteins, genes also control our inherited characteristics.
what are different versions of the same gene?
- there can be different versions of the same gene, which give different characteristics, like blue or brown eyes.
- the different versions of the same gene are called ALLELES.
what are alleles?
genes exist in alternative forms called alleles which give rise to differences in inherited characteristics.
what is the structure of DNA?
- a DNA molecule has two strands coiled together in the shape of a DOUBLE HELIX.
- the two strands are held together by chemicals called BASES.
- adenine (A) and thymine (T)
- cytosine (C) and guanine (G)
- the bases are paired, and they ALWAYS pair up in the same way. this is called complementary base pairing.
how are proteins made?
by reading the code in DNA
what are proteins made up of?
- proteins are made up of chains of molecules called amino acids.
- each protein has its own particular number and order of amino acids.
why does each protein have a specific function?
- the amino acid chains fold up to give each protein a different, specific shape - which means each protein can have a different function.
- this is why enzymes have active sites with a specific shape, and so only catalyse a specific reaction.
what decides the order of amino acids in a protein?
the order of bases in a GENE (a section of DNA that codes for a particular protein)
what is a codon?
each amino acid is coded for by a sequence of three bases in the gene. this is called a CODON.
what does DNA also contain?
- NON-CODING REGIONS.
- many regions of DNA are non-coding, this means they don’t code for any amino acids.
- despite this, some of these regions are still involved in protein synthesis.
how are proteins made?
in two stages:
- transcription
- translation
how does transcription occur?
- proteins are made in the cytoplasm by ribosomes. DNA is found in the nucleus and can’t move out of it because its really big. the cell needs to get the information from the DNA to the ribosome in the cytoplasm.
- this is done using messenger RNA (mRNA). like DNA, mRNA is made up of a sequence of bases, but its shorter and only a single strand. it also uses uracil instead of thymine as a base.
- RNA polymerase is the enzyme involved:
- RNA polymerase binds to a region of non-coding DNA in front of a gene
- the two DNA strands unzip and the RNA polymerase moves along one of the strands of the DNA.
- it uses the coding DNA in the gene as a template to make the mRNA. base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene.
- once made, the mRNA molecules moves out of the nucleus and joins with a ribosome in the cytoplasm.
how does translation occur?
- once the mRNA is bound to a ribosome, the protein can be assembled.
1. amino acids are brought to the ribosome by transfer RNA (tRNA)
2. the order in which the amino acids are brought to the ribosome matches the order of codons in mRNA.
3. part of the tRNA’s structure is called an ANTICODON, - it is complementary to the codon for the amino acid. the pairing of the codon and anticodon makes sure that the animo acids are brought to the ribosome in the correct order.
4. the amino acids are joined together by the ribosome. this makes a protein.
what are the differences between RNA and DNA?
- RNA is single-stranded
- RNA contains uracil instead of thymine
dominant
allele expressed in both homozygote and heterozygote
recessive
allele expressed only in homozygous genotype
homozygous
having 2 identical alleles
heterozygous
having 2 different alleles
phenotype
physical appearance
genotype
alleles an organism has
codominance
2 different alleles, both contribute to phenotype e.g. blood groups
what are most phenotypic features a result of?
- POLYGENIC INHERITANCE
- rather than single genes
how many pairs of chromosomes are there in every human body cell?
- the 23rd pair is labelled XX or XY, which determine whether you’re male or female.
what do males have?
- an X and a Y chromosome: XY
- the Y chromosome causes male characteristics
what do females have?
- an X and a X chromosome: XX
- the XX combination causes female characteristics
what are the chromosomes of eggs and sperm?
- all eggs have one X chromosome
- but a sperm can have either an X or a Y chromosome.
- so sex determination in humans depends on whether the sperm that fertilises an egg carries an X or Y
what does mitosis produce?
genetically idenctial cells
definition of mitosis
mitosis is when a cell reproduces itself by splitting to form two cells with identical sets of chromosomes.
what is the process of mitosis?
- Just before mitosis, each chromosome in the nucleus copies itself exactly (forms x-shaped chromosomes).
- Chromosomes line up along the centre of the cell where cell fibres pull them apart
- The cell divides into two; each new cell has a copy of each of the chromosomes
when does mitosis occur?
- growth
- repair
- cloning
- asexual reproduction
what does meiosis produce?
genetically different cells/gametes
how does a change in temperature affect enzyme function?
- a higher temperature increases the rate at first.
- the enzyme and substrate have more energy, so they move about more and are more likely to collide and form ENZYME-SUBSTRATE COMPLEXES.
- if it gets too hot, some of the bonds holding the enzyme together break.
- this changes the shape of the enzyme’s active site, so the substrate wont fit anymore
- the enzyme is said to be denatured.
- all enzymes have an optimum temperature they work best at.
how does pH affect enzyme function?
- if pH is too high or low, it interferes with the bonds holding the enzyme together.
- this changes the shape of the active site and denatures the enzyme.
- all enzymes have an optimum pH they work at (often 7, but not always)
how can you measure how temperature affects enzyme activity? (1)
YOU CAN MEASURE HOW FAST A PRODUCT APPEARS.
- the enzyme catalase in potatoes catalyses the breakdown of hydrogen peroxide into water and oxygen.
- you can collect the oxygen and measure how much is produced in a set time.
- use a pipette to add a set amount of hydrogen peroxide to a boiling tube. put the tube in a water bath at 10C.
- set up apparatus. add a source of catalase (e.g. 1cm3 of potato) to the HP and quickly attach the bung.
- record how much O2 is produced in the first minute. repeat 3 times and calculate mean.
- repeat at 20C, 30C and 40C.
- control any variable (e.g. pH, the potato used, size of potato pieces.
how can you measure how temperature affects enzyme activity? (2)
HOW FAST A SUBSTRATE DISAPPEARS
- the enzyme amylase catalyses the breakdown of starch to maltose.
- detect starch using iodine solution.
- set up apparatus. put a drop of iodine into each well of a spotting tile. every 10 seconds, drop a sample of the mixture into a well using a pipette, when the iodine solution remains brown (i.e. starch no longer present) record the total time takes.
- repeat with the water bath at different temperatures to see how it affects the time taken for the starch to be broken down. control all variables each time
how can you measure how pH affects enzyme activity?
- you can adapt temperature experiments to investigate the effect of pH on enzyme activity.
- follow the same method, but add a BUFFER SOLUTION with a different pH level to a series of different tubes containing the enzyme-substrate mixture.
- as before, control any variables, use the water bath to keep temp of reaction mixture the same for each pH, and make sure volumes and concs are kept same.
what does random fertilisation produce?
genetic variation of offspring
what is variation caused by in humans?
- genetic
- environmental
- combination of both
what is mutation?
random, rare changes to genetic code that can be inherited.
how can a change in DNA affect the phenotype?
- mutations change the sequence of the DNA bases in a gene, which produces a genetic variant (different form of the gene).
- as the sequence of DNA bases coded for the sequence of amino acids that make up a protein, mutations of a gene sometimes lead to changes in the protein it codes for.
- this can affect phenotypes.
how are enzymes affected by mutations?
- enzymes are proteins which need active site with a very specific shape to be able to work properly.
- a mutation in the gene that codes for an enzyme could lead to a change in the shape of an enzyme’s active site, altering its function.
- a mutation could also stop the production of the enzyme all together
what can mutations lead to and what does this increase?
can lead to a different phenotype, increasing variation.
what happens with most mutations?
- most mutations have no effect on the phenotype, they’re neutral.
- e.g. if the the mutation occurs in a non-coding region of DNA, the proteins structure and function will be unaffected.
- a mutation will also usually have no effect if it occurs in a recessive allele.
what happens very rarely with mutations?
- very rarely, a mutation will have a significant effect on phenotype.
- it might result in a very different protein which can no longer carry out its function.
- these mutations can be harmful, such as those that lead to cancer
- or beneficial, giving a survival advantage, e.g. antibiotic resistance in bacteria.
how can mutations occur?
- SPONTANEOUSLY
- when a chromosome doesn’t copy itself properly - CHANCE OF MUTATION INCREASED WITH EXPOSURE TO:
- ionising radiation e.g. X-rays, gamma rays or UV rays.
- chemicals called mutagens/carcinogens, e.g. chemicals in tobacco
what can resistance to antibiotics lead to?
- resistance to antibiotics can increase in bacterial populations
- such an increase can lead to infections being difficult to control.
what is Darwin’s theory of evolution?
- Individuals in a species show a wide range of VARIATION caused by DIFFERENCES IN GENES
- Individuals with characteristics most suited to the environment have a HIGHER CHANCE OF SURVIVAL and more chances to REPRODUCE
- Therefore these characteristics are PASSED TO THEIR OFFSPRING AT A HIGHER RATE than those with characteristics less suited to survival
- Over many generations, these beneficial characteristics become MORE COMMON IN THE POPULATION and the species changes (the SPECIES EVOLVES)
- This idea of natural selection became known as ‘survival of the fittest’
