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| Question | Answer |
| 3.4 Genetic information, variation and relationships between organisms | N/A |
| 3.4.1 DNA, genes and chromosomes | N/A |
| What is DNA like in prokaryotic cells? | - Short - Circular - Not associated with proteins |
| What is a plasmid? | A short section of circular DNA in prokaryotic cells that is separate to the main strand. |
| What is DNA like in eukaryotic cells? | - long - linear - associated with proteins, called histones |
| What is a chromosome? | The structure formed of DNA and histones. |
| Where is DNA found in eukaryotic cells? | - Nucleus - Mitochondria - Chloroplasts |
| What is DNA like in mitochondria & chloroplasts? (eukaryotic cells) | - Short - Circular - Not associated with proteins |
| What do genes code for? | - Amino acid sequences of polypeptides - A functional RNA |
| Where are genes located? | In a fixed position on DNA molecule (Locus) |
| What is a section of three DNA base pairs called? | - Triplet - Codon |
| What do sections of three DNA base pairs do? | Code for a specific amino acid |
| What are the three traits of the genetic code? | - Universal (same for all organisms) - Non-overlapping (Each triplet of base pairs codes separately) - Degenerate (Amino acids can be coded for by more than one codon) |
| What can be found between genes? | Non-coding multiple repeats of base sequences |
| What is the name for a codon that does not code for a polypeptide? | Intron |
| What is the name for a codon that codes for a polypeptide? | Exon |
| 3.4.2 DNA and protein synthesis | N/A |
| What is the genome? | The complete set of DNA within a cell or organism. |
| What is the proteome? | The full range of proteins that a cell or organism is able to produce. |
| What is the structure of messenger RNA (mRNA) like? | - Short - Single helix |
| Diagram of an mRNA molecule | |
| What is the structure of transfer RNA (tRNA) like? | - Very short - Clover-like structure - Amino acid attachment site on one end - Anticodon loop opposite amino acid attachment site |
| Diagram of a tRNA molecule | |
| What is transcription? | The process of pre-mRNA production from DNA (occurs in Nucleus) |
| How does transcription differ in prokaryotic cells to eukaryotic cells? | In prokaryotic cells, mRNA is produced directly from DNA |
| What are the steps involved in transcription? | - DNA 'unzipped' by DNA helicase which catalyses the breakdown of hydrogen bonds between base pairs - Free nucleotides arrive from around base pairs and form hydrogen bonds with one of the DNA strands - RNA polymerase catalyses the formation of strong chemical bonds between phosphate-sugar part of nucleotides, forming a long 'backbone' - pre-RNA leaves nucleus through nuclear pores, splicing occurs at this point |
| What is splicing? | The process of removing non-coding codons from the pre-mRNA molecule, forming mRNA - occurs on the inside of nucleus, by the nuclear pores |
| What are the steps involved in splicing? | - Pre-mRNA is attacked just before it leaves the nucelus through the nuclear pores by spliceosomes - Spliceosomes catalyse the removal of introns from the structure, leaving only exons and thus forming mRNA |
| What is translation? | The process during which mRNA is decoded to produce a specific polypeptide which can fold into a protein - occurs in ribosomes |
| What are the three stages of translation? | - Initiation - Elongation - Termination |
| What happens during the initiation phase of translation? | - Small ribosomal subunit binds with mRNA - Small subunit moves along mRNA until it reaches the start codon (AUG) - Matching anti-codon of tRNA (with methianine) binds with start codon - Large subunit moves on top and acts as stapler to start |
| What happens during the elongation phase of translation? | - Additonal tRNA anticodons attach to mRNA codons - Amino acids attached to the tRNA molecules attach to one another by means of peptide bonds - tRNA releases amino acids to pick up further amino acids - mRNA shifts along the large subunit by one codon, first tRNA molecule leaves, new tRNA molecule enters - this repeats until termination |
| hen does the termination phase of translation occur? | When a stop codon in the mRNA is bound to the ribosome |
| What happens during the termination phase of translation? | - Ribosome accepts a protein called a release factor - Release factor causes the addition of a water molecule instead of an amino acid - This reaction releases the protein and the translation assembly comes apart |
| 3.4.3 Genetic diversity can arise as a result of mutation or during meiosis | N/A |
| What is a mutation? | Any change in the quantity of base sequences of DNA |
| What is a gene mutation? | A change to one or more bases or the sequence of bases in DNA |
| What is substitution of bases? | One or more of the bases in DNA is replaced by a nucleotide with a different base |
| Diagram of base substitution | |
| What is a nonsense mutation? | A substitution mutation in which a stop codon is prematurely coded, causing the polypeptide to be shortened |
| What is a mis-sense mutation? | A substitution mutation in which a codon is changed and thus a different amino acid is coded for, leading to a different polypeptide |
| What is a silent mutation? | A substitution mutation in which a codon is changed but the same amino acid is coded for due to the degeneracy of the genetic code, leading to no impact |
| What is Thalassemia? | - Caused by nonsense mutation? - Autosomal recessive blood disease - Results in reduced rate or no synthesis of one of globin chains that make up haemoglobin - Results in anaemia (deficiency of red blood cells) |
| What is a sickle-cell anaemia? | - Caused by mis-sense mutation - Occurs due to a mutation in the haemoglobin gene - Hydrophilic amino acid Glutamic acid is replaced by the hydrophobic acid Valine - This distorts the shape of the red blood cell and decreases its elasticity, resulting in a fixed sickle-like shape that clogs blood vessels slowing flow |
| What is base deletion? | - Nucleotide lost from the normal DNA sequence - Leads to frame shift as DNA is non-overlapping - All subsequent triplets are changed as the code 'shifts to the left' (in reality it doesn't, the gap is simply skipped) |
| Base deletion diagram | |
| What is Tay-Sachs disease? | - caused by deletion of bases - autosomal recessive disorder - causes relentless deterioration of mental and physical abilities that commences around 6 months of age and results in death by age of four - caused by insufficient activity of the enzyme hexosaminidase, found in lysosomes and responsible for the breakdown of lipds (lysosomes are inactive due to frame-shift in coding enzyme) - without this, lipids accumulate in the brain and interfere with biological processes |
| What is a chromosome mutation? | A change in a chromosome or a whole set of chromosomes |
| What is a change in a whole set of chromosomes? | - when organism has three or more sets of chromosomes rather than two - called polyploidy - mainly occurs in plants (results in infertility, often found in wheat, tobacco, potato, banana, strawberry) |
| What is a change in the number of individual chromosomes? | - caused by non-disjunction during meiosis (when homologous pairs fail to split) - results in additional or fewer chromosomes |
| What is Down's syndrome? | Chromosome 21 is the smallest chromosome (40 million nucleotide pairs, 1.5% of DNA) - causes delayed growth and development - additional chromosome could be from a completely different pair - many codons affected so there are many different causes |
| What is a mutagenic agent? | A chemical agent that increases the rate of genetic mutation |
| What is meiosis? | - cell division creating gametes - Made up of two divisions: Miosis I & Miosis II |
| What happens during Meiosis I? | Mitosis cell division: - Interphase - Prophase (including independent segregation and crossing over/recombination) - Metaphase - Anaphase - Telophase |
| What is independent segregation? | - During Meiosis I the homologous chromosomes line up alongside their partner after they have replicated - There are two possible ways in which these pairs can line up, increasing the chance of variation in offspring |
| What is crossing over and recombination? | - When the homologous chromosomes line up, they become entangled and twist many times, crossing over - This can result in sections of chromosomes breaking off and re-joining to the opposite chromosome, recombining and increasing variation |
| What does Meiosis I look like? | |
| What happens during Meiosis II? | - Prophase - Metaphase - Anaphase - Telophase |
| What does Meiosis II look like? | |
| How is the number of possible gamete variations in gametes calculated? | 2^number of homologous pairs |
| How is the number of possible varieties in zygotes calculated? | Number of variations in gametes of parents multiplied together |
| How does random fertilisation increase variation in offspring? | Greater chance of parents with different gametes, increasing the number of chromosome combinations in the zygote |
| 3.4.4 Genetic diversity and adaptation | N/A |
| What is genetic diversity? | The number of different alleles in a population |
| How does genetic diversity affect natural selection? | It allows it to occur |
| What are the principles of natural selection in evolution? | - Random mutation can result in new alleles - Many mutations are harmful, but some can result in advantages leading to greater reproductive success - Advantageous alleles that allow greater reproductive success are passed on to future generations - Over generations the proportion of the population with the new allele increases until it becomes the norm |
| What is directional selection? | Natural selection that favours organisms at the extremes e.g. antibiotic-resistant bacteria become the norm |
| Directional selection diagram | |
| What is stabilising selection? | Natural selection that favours organisms with average characteristics e.g. birth weights of babies, with those close to the mean weight having a greater likelihood of survival |
| Stabilising selection diagram | |
| What is the outcome of natural selection? | Species that are better adapted to their environment/conditions |
| What are the types of adaptation? | - Anatomical - Physiological - Behavioural |
| What is an anatomical adaptation? | Physical change to organism's anatomy that makes it better adapted to the environment e.g. white fur of polar bear |
| What is a physiological adaptation? | Change to an organism's internal reactions/chemical processes e.g. venom production in some snakes |
| What is a behavioural adaptation? | Change to an organism's behaviour that makes it better adapted to the environment/better able to survive e.g. changing migration patterns of birds to warmer climates |
| 3.4.5 Species and taxonomy | N/A |
| What is a species? | A group of organisms with similar characteristics capable of producing fertile offspring |
| What is the role of courtship behaviour in ensuring successful mating? | Ensure that fertile offspring are produced |
| What are the steps of the courtship process? | - Recognise members of own species - Identify a mate of the opposite sex - Synchronise mating and fertility - Ensure sexual maturity - Form a pair bond - Mate |
| What is a phylogenetic classification system? | - Arranges species into groups based on evolutionary origins and relationships - Uses heirachical, non-overlapping system made up of groups called taxa |
| What is the binomial classification? | Developed by Carl Linnaeus in 18th century - Made up of seven hierachical groups - Species are referred to double name made up Genus and species e.g. Homo sapiens (italicized/underlined) |
| What does Linnaeus' classification look like? | |
| How can species be classified? | - Examining DNA - Breeding experiments - Fossil records - Patterns of embryonic development |
| 3.4.6 Biodiversity within a community | N/A |
| What is biodiversity? | - Variety of life within a given area Area can be of any size |
| What is an ecosystem? | Self-contained, self-supporting combination of interacting biotic (living) and abiotic (components) - Made up different populations (inter-breeding groups) of species - Comprises many interacting communities within many habitats |
| What is species richness? | Measure of the number of different species in a community |
| What kinds of diversity are there? | - Species diversity - variety of species within ecosystem - Genetic diversity - variety of genes/alleles within ecosystem - Ecosystem diversity - variety of different habitats within an ecosystem |
| How is species diversity measured? | Considering number of different species, and number of each species present D = diversity index N = total number of species n = number of each species present |
| How can humans affect the environment? | - Habitat loss - Introduced species - Population growth of humans - Pollution - Over-consumption of resources |
| How can agriculture reduce biodiversity? | - Destruction of habitats to clear land e.g. removal of hedges to enlarge fields - Over-grazing of land destroying vegetation e.g. sheep grazing same area of grassland - Creation of monocultures (single species ecosystem) - Use of pesticides/insecticides can kill species |
| How can agricultural methods be improved to support biodiversity? | - Use of hedges as natural partitions - Leave wet corners of fields rather than draining - Reduce of pesticides/insecticides - Maintaining ponds and creating new ones - Use crop rotation including nitrogen fixing plants (that trap nitrogen and release it into the soil when they break down) to naturally boost fertility |
| 3.4.7 Investigating diversity | N/A |
| How can genetic diversity within or between species be observed? | - frequency of measurable/observable characteristics - base sequence of DNA - base sequence of mRNA - amino acid sequence coded for by mRNA |
| How can quantitative data relating to variation within a species be gathered? | - Gathering data from random sampling using transects and quadrats at regular intervals/quadrats placed at random positions over an area - Mean and standard deviation of data calculated - Data interpreted or extrapolated to estimate diversity over a wider area |
| How has gene technology changed methods of investigating diversity? | - Change from unreliable methods of comparing anatomical features (flawed as characteristics coded for by more than one gene and affected by environment - change to DNA and mRNA base sequence comparison - bases read and displayed by computers and given fluorescent dye A(green), T(red), C(blue), G(yellow) |
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