Coordination, Response and Gene Technology flashcards

Topic 8: Coordination, Response and Gene Technology

Sensory vs relay vs motor neurone

Sensory: receptor to CNS; cell body off to one side, outside the cord. Relay: inside the CNS; short. Motor: CNS to effector; cell body in the CNS; long axon.

Spinal reflex arc

Receptor → sensory neurone enters the cord by the dorsal root → synapse with a relay neurone in the grey matter → synapse with a motor neurone → leaves by the ventral root → effector. Fast: short pathway, few synapses, no conscious thought.

Values for resting potential, threshold and peak

Resting potential about −70 mV; threshold about −55 mV; peak about +40 mV. The Na⁺–K⁺ pump moves 3 Na⁺ out and 2 K⁺ in, using ATP.

Events of an action potential

Voltage-gated Na⁺ channels open and Na⁺ diffuses in; at threshold many more open, giving rapid depolarisation. At the peak Na⁺ channels shut and voltage-gated K⁺ channels open: K⁺ out, repolarisation. Slow-closing K⁺ channels cause brief hyperpolarisation.

Maximum impulse frequency for a refractory period of 5.0 ms

Maximum frequency = 1 ÷ refractory time = 1 ÷ 0.0050 s = 200 per second.

How is stimulus strength coded in a neurone?

Action potentials are all-or-nothing, always the same size. A stronger stimulus gives a higher frequency of impulses and stimulates more neurones.

How does a rod cell respond to light?

Rhodopsin absorbs light and splits into opsin and retinal. Cation channels close, Na⁺ stops entering and the rod hyperpolarises, releasing less neurotransmitter. The bipolar neurone is no longer inhibited, depolarises, and an action potential passes along the optic neurone.

Habituation

A reduced response to a stimulus repeated many times that is neither harmful nor rewarding. Usually fewer Ca²⁺ ions enter the presynaptic neurone, so less neurotransmitter is released. A new stimulus still gives a full response.

Phytochrome

A plant pigment with two forms: Pr absorbs red light (about 660 nm) and becomes Pfr; Pfr absorbs far-red (about 730 nm) and becomes Pr. Pfr affects transcription, controlling germination, etiolation and flowering.

How does IAA cause phototropism in a shoot?

With light from one side, IAA moves to the shaded side. Proton pumps lower the wall pH there, so those cells elongate more and the shoot bends towards the light.

Investigating gibberellin and amylase in cereal grains

Place grain halves (with and without embryo) on starch agar, with or without gibberellic acid. Remove the grains and flood with iodine: clear zones show starch digested by amylase. Control: boiled grain halves.

Making recombinant DNA

Cut the gene and the plasmid with the same restriction endonuclease to give complementary sticky ends; mix so they anneal by hydrogen bonds; DNA ligase seals the backbone with phosphodiester bonds. Include a promoter that works in the host.

Why use cDNA when putting a human gene into bacteria?

cDNA is copied from mRNA by reverse transcriptase, so it has no introns. Bacteria cannot splice out introns.

Methods of getting DNA into bacteria, plants and animals

Bacteria: transformation using calcium chloride and heat shock, or electroporation. Plants: Agrobacterium tumefaciens with the gene in its Ti plasmid, or a gene gun. Animals: microinjection into a fertilised egg, viral vectors, liposomes.

How are transformed cells identified?

Antibiotic-resistance marker: only transformed cells grow on that antibiotic. Fluorescent marker (GFP): transformed cells glow under UV light. Insertional inactivation: an insert in a resistance gene makes recombinants lose that resistance.

A 5000 bp circular plasmid is cut at two sites 1100 bp apart. What fragments form?

Two fragments: 1100 bp and 5000 − 1100 = 3900 bp. (A circular molecule cut n times gives n fragments.)