AS Level AQA Biology: Unit 4 (Genetic information, variation and relationships between organisms)

Big Dave
Flashcards by Big Dave, updated more than 1 year ago
Big Dave
Created by Big Dave almost 4 years ago


AS - Level Biology (Unit 4) Flashcards on AS Level AQA Biology: Unit 4 (Genetic information, variation and relationships between organisms), created by Big Dave on 11/28/2016.

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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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