Grey Matter - Topic 8

Question 1

Distinguish between each of the following:
(a) Sensory neurone and motor neurone

Answer 1

• Sensory neurones carries impulses from the receptor where’s motor neurones carries impulses to a muscle/gland
• Sensory carry impulses to the CNS, motor carries away from CNS
• Motor has many short dendrites, sensory has one long dendron

Question 2

What neurone is this and why?

Name the neurone and give a reason why

Answer 2

Motor as the cell body is at one end

Question 3

What neurone is this and give it’s function

Answer 3

Sensory and its function is to conduct impulses from receptor to the CNS

Question 4

What is the structure of a myelin sheath?

Answer 4

Myelin sheath contains Schwann cells that wrap and fold around the axon.
They are fatty lipids in nature with nodes as gaps in the sheath and speed up the electrical impulses for a rapid responses.

Question 5

Explain the effect of opioids on the diameter of the pupil, between one and five hours after exposure to a flash of light.

Answer 5

Pupils constrict as time passes with opioids, due to circular muscles stimulated and radial muscles are inhibited. Meaning the parasympathetic nerve pathway is inhibited whilst the sympathetic nerve pathway is stimulated

Question 6

Describe the functions of the enzymes used to genetically modify bacteria.

Answer 6

• Restriction endonuclease used to cut the plasmid
• To form sticky ends
• Ligase enzyme used to add gene to plasmid
• Ligase forms phosphodiester bonds between nucleotides
• Recombinant DNA/ Plasmid is produced

Question 7

Explain how an enzyme is involved in joining the two different genes together

Answer 7

• DNA ligase joins the two genes
• by forming phosphodiester bonds
• Via condenstation reactions

Question 8

Which enzymes can be used to cut open the plasmids

Answer 8

Restriction endonuclease

Question 9

Plamids are placed inside a type of bacteria and then exposed to an antibiotic.
(iii) Explain why antibiotic A is used in stage 3.

Answer 9

• So the bacteria with the antibiotic resistance gene will survive
• Therefore the bacteria will have the gene for (any characteristic named)

Question 10

Glucosaminoglycans (GAGs) are the by-products of chemical reactions inside cells. GAGs are broken down by enzymes inside lysosomes in cells.
Mucopolysaccharidosis type I (MPS I) is a genetic condition that results in the build-up of GAGs inside cells.
MPS I affects the production of enzyme G that breaks down GAGs inside lysosomes.
More than 50 different mutations in the gene for enzyme G have been found to result in MPS I. Most of these mutations involve changing a single base in the gene.
(i) Explain how a single base mutation can lead to an altered primary structure of enzyme G.

Answer 10

• Changing a base results in a change in triplet code
• So the codon in the mRNA will change
• Resulting in different amino acid structure thus different primary structure.

Question 11

(ii) Explain how human genome sequencing can be used to identify the mutations associated with MPS I.

Answer 11

• Sequence the genome of people with MPS1
• Sequence the genome of a number of people without the condition
• Compare the base sequences and work out mutations only found in individuals with this condition.

Question 12

Explain why genetically modified bacteria delivering drugs ‘to the exact tissue in the body where they’re needed and nowhere else’ would decrease side effects.

Answer 12

• Drugs not delivered to other/healthy tissues. The drug does not deliver to the whole body
  -Overall dosage is needed less and a higher concentration can be delivered to target area

Question 13

What describes the genome of an adult male?

Answer 13

• All of his introns plus all of his exons

Question 14

Which types of organism can be both genetically modified and be a
source of a gene to be used in GM?

Answer 14

Animal, bacteria and plant

Question 15

The neurones of the central nervous system contain TAU proteins. These proteins help to maintain cell structure.
In humans, six different TAU proteins can be produced from a single gene.
Parkinson’s disease has been linked to the different forms of the TAU proteins present in neurones.
Scientists are studying the effect of these different TAU proteins in animal models. One model used is the fruit fly, Drosophila.
a) Describe how Drosophila flies could be genetically modified to produce one form of the human TAU protein.

Answer 15

• Extract mRNA for one form of the (tau protein)
  -copy mRNA into DNA
  -Use restriction enzymes to create sticky ends/ cut the DNA and a vector
• ligate/integrate/insert the TAU DNA into the vector DNA
  -Introduce vector into fertilised egg/embryonic stem/zygote/cells/neural cell stem cells.

Question 16

Describe how bacteria can be genetically modified to produce a cytokine for the treatment of neurological and mental disorders

Answer 16

• Isolate gene for cytokine
• use a bacterial plasmid as a vector
• Cut the human DNA and the plasmid using the same restriction enzyme
• Splice the gene and plasmid together using DNA ligase
• Put the modified plasmids into bacterial cells

Question 17

Spider silk is a very strong and flexible natural fibre. It is of interest to humans as a possible fibre for protective clothing.
Scientists have genetically modified a range of organisms to produce spider silk, including goats and plants such as alfalfa.
Give two reasons why some people may be concerned about the use of genetically modified alfalfa as a source of spider silk.

Answer 17

• The transfer of antibiotic-resistance gene to other microorganisms
• Could lead to pathogenic bacteria developing resistance to antibiotics

Question 18

Glucosaminoglycans (GAGs) are the by-products of chemical reactions inside cells. GAGs are broken down by enzymes inside lysosomes in cells.
Mucopolysaccharidosis type I (MPS I) is a genetic condition that results in the build-up of GAGs inside cells.
MPS I affects the production of enzyme G that breaks down GAGs inside lysosomes.
More than 50 different mutations in the gene for enzyme G have been found to result in MPS I. Most of these mutations involve changing a single base in the gene.
A biotechnology company is developing a method of repairing the mutations in the gene for enzyme G.
The method being developed is called CRISPR-Cas9.
In this method, a short sequence of RNA binds to the DNA containing the mutation responsible for MPS I.
This RNA acts as a guide to enable the Cas9 enzyme to bind to DNA. This enzyme can then cut and repair the DNA, removing the mutation.

(i) Describe how scientists could produce this short sequence of RNA needed to treat someone with MPS I.

Answer 18

• Transcription of the DNA containing the mutation
• Using RNA nucleotides/ RNA polymerase

Question 19

Explain why the use of CRISPR-Cas9 technology can be described as personalised medicine.

Answer 19

• Individuals have different mutations/ target an individual’s specific mutation
  -The RNA molecule used will be specific to each mutation thus individual.

Question 20

There are various ways to scan the brain.
Describe how positron emission tomography (PET) scans can be used to investigate brain structure.

Answer 20

• PET makes use of radioactive tracers/markers/glucose
• PET scan detects emission of positrons/production of gamma rays
• Provides 3D image

Question 21

(ii) Name the type of learning behaviour shown by the child as they were repeatedly shown a cheeseburger.

Answer 21

Habituation

Question 22

(iii) Explain what happens at the synapse to cause a decrease in saliva production
when the child was shown a cheeseburger on more than six occasions.

Answer 22

• Calcium ion channels become less responsive
• Fewer vesicles move towards/fuse with the presynaptic membrane
• Therefore less neurotransmitter binds to receptors on the post-synaptic membrane
• Thus membrane may not be depolarised/ action potential may not occur

Question 23

Visual development requires exposure of the visual cortex to environmental signals during a critical period.
Describe the role of visual stimulation on the development of the visual cortex during the critical period.

Answer 23

• Ocular dominance columns develop in the visual cortex
• Neurones will form synapses with these columns
• Stimuli/action potentials/ impulses along neurones required to strengthen connections with cells of ocular dominance columns
• Stimulation during the critical period is needed to form effective connections in the visual cortex

Question 24

(ii) Functional MRI (fMRI) measures brain activity by detecting changes in __________________?

Answer 24

Blood flow

Question 25

Which of the following types of scanner uses X-rays?

Answer 25

CT

Question 26

Which of the following terms describes a change in response as a result of repeated stimulation?

Answer 26

Habituation

Question 27

The retina of the human eye contains rod cells.
These cells detect light energy as photons.
The light energy is converted to a nerve impulse that is interpreted by the brain.
(i) The transmission of an impulse between a neurone in the optic nerve and a cell in the brain involves ions and neurotransmitter molecules.
Describe how these ions and neurotransmitter molecules are involved in the transmission of an impulse.

Answer 27

• Calcium ions enter presynaptic neurone so vesicles with neurotransmitter can fuse with the pre-synaptic membrane
• Neurotransmitter molecules diffuse across the synapse
• Neurotransmitter bind with receptors on post-synaptic membrane on the brain cell
• Sodium ions diffuse into brain cell/post-synaptic cell leading to a depolarisation/action potential

Question 28

The non-protein part of the light-absorbing pigment in the rod cells of the retina is called ______________

Answer 28

Retinal

Question 29

(iii) Explain how fMRI can be used to identify the part of the brain involved in interpreting
information from the visual cortex.

Answer 29

• fMRI detects blood flow/oxygen use in the brain
• Increased brain activity results in increased blood flow/demand for oxygen/ aerobic respiration In the area of activity
• Oxyhaemoglobin absorbs fewer radio waves/fMRI detects areas where less signal absorbed

Question 30

It is safer to use MRI than computed tomography (CT) because __________________

Answer 30

CT uses X-rays that can cause mutations in the DNA of muscle fibres

Question 31

Muscle cells contain myofibrils. The diagrams show the arrangement of some of the molecules present in a myofibril when calcium ions are absent and when they are present.
Describe how the concentration of calcium ions around the myofibrils is controlled.

Answer 31

• Calcium ions released from the sarcoplasmic reticulum
• In response to nerve impulse/action potential/depolarisation at neuromuscular junction
• Calcium channels opens to allow calcium ions to cross the membrane/enter the sarcoplasm
• Calcium ions taken back up to the sarcoplasmic reticulum by active transport.

Question 32

The muscles of the earthworm (Lumbricus terrestris) contract when it is touched. This is known as the withdrawal response.
Contraction of the muscle in the withdrawal response is stimulated by nerve impulses. These nerve impulses can be detected using electrodes.
Explain the electrical changes in an axon that allow these nerve impulses to be detected.

Answer 32

• Potential difference across the axon changes
• This is due to sodium channels opening
• Sodium ions move into the axon and cause depolarisation
• Followed by potassium channels opening
• Potassium ions move out of the axon causing repolarisation

Question 33

People with Guillain-Barré syndrome (GBS) suffer from a rapid onset of muscle weakness. It is thought that GBS is caused by damage to the peripheral nervous system.
In individuals with GBS, the immune system attacks and destroys the myelin sheath surrounding some neurones.
Neurone conduction was studied in an individual with GBS and in an individual without GBS. The results are shown in the table.
Explain why GBS caused muscle weakness in this individual.

Answer 33

• No difference in action potential between individual with and without GBS
• Motor neurone conduction speed is reduced
• Due to loss of myelin/ demyelination of motor neurone
  -Therefore loss of saltatory conduction

Question 34

(ii) The axons of some neurones are surrounded by a myelin sheath.
The main component of myelin is a glycolipid. Glycolipids are formed from lipids attached to a chain of __________________

Answer 34

Sugar molecules joined by glycosidic links

Question 35

(iii) Describe the role of the dendrites in a neurone.

Answer 35

• Form synapses/connections with other neurones
• Receive impulses from other neurones
  -Involved in summation
• initiate action potential

Question 36

(i) Explain how nicotine causes an action potential in the post-synaptic neurone that releases noradrenaline.

Answer 36

• Nicotine is similar in shape to acetylcholine
• Increases permeability of membrane to sodium ions
• Nicotine causes the depolarisation of the post-synaptic membrane
• Depolarisation reaches threshold

Question 37

(ii) State how an increase in calcium ion uptake by the neurone leads to the release of noradrenaline.

Answer 37

Calcium ions cause vesicles containing noradrenaline to fuse with the presynaptic membrane

Question 38

Compare and contrast the structure of a sensory neurone and a motor neurone

Answer 38

Similarities:
-Both have cell body with nucleus
-Both have axon
-Both have dendrites at one end and terminal branches on other end

Difference:
- Motor cell body at the end
-Sensory cell body is located along the axon

Question 39

Acetylcholinesterase is an enzyme involved in regulating the transmission of nerve impulses across some synapses.
Alzheimer’s disease is associated with the loss of neurones that produce acetylcholine.
It has been suggested that inhibitors of acetylcholinesterase may be useful in the treatment of Alzheimer’s disease.
(i) Explain why inhibitors of acetylcholinesterase could be useful in the treatment of Alzheimer’s disease.