AQA Unit 5 Biology

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  • Created by: Ella
  • Created on: 06-04-14 14:34
What is a gene?
A sequence of bases in a DNA molecule that codes for a protein (polypeptide)
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What bonds are present in the primary structure of a protein?
Peptide bonds
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What bonds are present in the secondary structure of a protein?
Hydrogen bonds
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What bonds are present in the tertiary structure of a protein?
Ionic, hydrogen and disulphide bonds.
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Name 3 ways in which RNA is different from DNA
The sugar in RNA is a ribose sugar. The nucleotides form a single polynucleotide strand. Uracil (U) replaces Thymine as a base.
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What are the two types of RNA?
Messenger RNA (mRNA) and transfer RNA (tRNA)
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What is the role of mRNA?
It carries the genetic code from the DNA in the nucleus to the cytoplasm where it's used to make a protein during translation.
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What is the structure of mRNA
A single polynucleotide strand
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Where is mRNA made?
In the nucleus (during transcription)
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What is a codon?
A group/specific sequence of 3 adjacent bases in an mRNA molecule.
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What is the role of tRNA?
It carries the amino acids that are used to make proteins to the ribosomes.
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What is the structure of tRNA?
It's a single polynucleotide strand that's folded into a clover shape, held by hydrogen bonds that form between specific base pairs.
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Where is tRNA found?
In the cytoplasm (where it's involved in translation).
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What is an anticodon?
A specific sequence of 3 bases at one end of the tRNA molecule
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What is a transcription factor?
A (protein) molecule that has a site that binds to specific regions of the DNA in the nucleus
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What do transcription factors do?
They control gene expression by controlling the rate of transcription of target genes
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What are activators?
Transcription factors that increase the rate of transcription by helping RNA polymerase to bind to the start of a target gene.
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What are repressors?
Transcription factors that decrease the rate of transcription by binding to the start of a target gene which inhibits/blocks/prevents RNA polymerase binding.
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What is siRNA?
Short, double-stranded RNA molecules that can interfere with the expression of specific genes.
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What is a stem cell?
Unspecialised cells that can develop/divide into other types of (specialised) cells
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What is a totipotent cell?
Stem cells that can mature (develop) into any type of body cell in an organism. Totipotent stem cells in humans are only present in the early life of an embryo.
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What is tropism?
A growth movement/response of a plant to to a directional stimulus
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What are the 4 types of tropism in plants?
Positive phototropism, negative phototropism, positive geotropism, negative geotropism.
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What are Auxins and what do they do?
Auxins are growth factors that stimulate the growth of shoots by cell elongation.
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What is cell elongation?
Where the cell walls become 'stretchy' and loose so the cell gets longer.
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How does indoleacetic acid cause cell elongation?
It increases the H+ conc. in the cell walls, which weakens the bonds between the cellulose fibres. The cell then expands due to water moving into the cell by osmosis and causes elongation. The cell walls then reform.
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What is kinesis?
A response in which the organism doesn't move towards or away from a stimulus (stimulus is non-directional).
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What is taxes?
A response in which an organism moves towards or away form a directional stimulus.
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What are chemical mediators?
Substances that are released from certain mammalian cells (mostly injured or infected) that cause small arteries & arterioles to dilate which leads to a rise in temp. and swelling in infected area.
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Give two examples of chemical mediators...
Histamine (for swelling, redness & itching) and Prostaglandins (affects blood pressure and neurotransmitters).
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What is a stimulus?
A detectable change in the internal or external environment that produces a response in the organism.
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What is the central nervous system made up of?
The brain and the spinal cord
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What is the Peripheral nervous system made up of?
The peripheral NS is made up of pairs of nerves that connects the CNS to the rest of the body.
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What two different systems make up the peripheral NS?
The Somatic NS and Autonomic NS
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What does the Somatic NS control?
Conscious activites
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What does the Autonomic NS control?
Unconscious activites
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What two systems make up the Autonomic NS?
The Sympathetic NS and Parasympathetic NS
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What does the Sympathetic NS do?
Stimulates effectors & so speeds up any activity ('flight or fight response')
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What does the Parasympathetic NS do?
Inhibits effectors & so slows down any activity (the 'rest & digest' system)
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What do sensory neurones do?
Transmit nerve impulses from a receptor to an intermediate or motor neurone.
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Why is the reflex arc important?
It's involuntary (doesn't require the brain's decision making) so doesn't overload the brain with situations where the response is always the same. They protect the body from harmful stimuli and are fast which is important for withdrawal.
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What do baroreceptors do and where are they in the body?
They monitor changes in blood pressure and are located within the walls of the carotid arteries & aorta
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What do chemoreceptors do and where are they in the body?
They monitor the changes in the partial pressure of CO2 in the blood plasma and are located in the walls of the carotid arteries
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What is the potential difference?
The difference in voltage across the membrane of a cell
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What is the resting potential?
When a nervous system receptor is in its resting state (not being stimulated) and the outside of the membrane is more positively charged compared to the inside.
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What is the generator potential?
The change in potential difference due to a stimulus
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What is an action potential and when is it triggered?
An action potential is an electrical impulse along a neurone where the inside of the membrane is more positive than the outside (the membrane is said to be depolarised) which is triggered when the generator potential is big enough.
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What are pancinian corpuscles?
Pressure receptors in the skin which detect mechanical stimuli
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What is the refractory period?
The length of time between action potentials.
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Why does the refractory period occur?
The ion channels are recovering (the Na+/K+ pump is returning the membrane to its resting potential) & so can't be made open
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What are the two types of refractory period?
The absolute refractory period and the relative refractory period
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What is the absolute refractory period?
The periods of de-& re-polarisation of a neurone membrane
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What is the relative refractory period?
The period of hyperpolarisation & rebalancing of Na+ and K+ concentrations
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What is a synapse?
The point where the axon of one neurone connects with the dendrite of another or with an effector.
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What is spatial summation?
Where a number of different presynaptic neurones together release enough neurotransmitters to exceed the threshold value of the post-synaptic neurone & so together trigger a new action potential.
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What is temporal summation?
A single pre-SN releases neurotransmitters many times over a short period. If the total amount of neurotransmitters exceeds the threshold value of the post-SN, then a new action potential is triggered
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What do excitatory neurotransmitters do?
They depolarise the post-synaptic membrane which makes it fire an action potential if the threshold is reached
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Give an example of an excitatory neurotransmitter...
Acetylcholine (ACh) - which binds to cholinergic receptors to cause an action potential
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What do inhibitory neurotransmitters do?
They hyperpolarise the post-synaptic membrane which makes the potential difference more negative & preventing it from firing an action potential
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Give an example of an inhibitory neurotransmitter...
GABA - which binds to receptors & causes K+ ion channels to open
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What is a neuromuscular junction?
The point where a motor neurone meets a skeletal muscle
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Name the 3 types of muscle found in the body...
Cardiac muscle, smooth muscle and skeletal muscle
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What is actin?
A thin fibrous protein filament which consists of two strands twisted around one another and has binding sites for globular myosin heads
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What is myosin?
A thick fibrous protein filament which consists of long rod-shaped fibres with 'bulbus heads' (made from a globular protein) that project to the sides
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What are the light bands of a myofibril called?
The isotropic band (or I-band)
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What are the dark bands of a myofibril called?
The anisotropic band (or A-band)
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What is the H-zone?
The lighter region at the centre of the anisotropic band
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What is the Z-line?
The line at the centre of the isotropic band
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What is the sarcomere?
The distance between adjacent Z-lines
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