UNIT 1 - KA4

Question 1

Where do multicellular organisms signal between

Answer 1

Multicellular organisms signal between cells using extracellular signalling molecules

Question 2

What are examples of extra cellular signalling molecules

Answer 2

Steroid hormones, peptide hormones, and neurotransmitters are examples of
extracellular signalling molecules.

Question 3

What are receptor molecules of target cells

Answer 3

Receptor molecules of target cells are proteins with a binding site for a specific signal molecule

Question 4

What effect does binding have on the receptor

Answer 4

Binding changes the conformation of the receptor, which initiates a response within the cell

Question 5

What do different cell types produce

Answer 5

Different cell types produce specific signals that can only be detected and responded to by cells with the specific receptor

Question 6

What effects may signalling molecules have on different target cell types

Answer 6

Signalling molecules may have different effects on different target cell types due to
differences in the intracellular signalling molecules and pathways that are involved.

Question 7

What may different cell types show to the same signal

Answer 7

In a multicellular organism, different cell types may show a tissue-specific response to
the same signal

Question 8

What is a tissue specific response to a signal molecule

Answer 8

With a multicellular organism the response may be tissue specific (ie the same signal molecule may bring about a different response depending on the cell type it binds)

Question 9

When does signal transduction occur

Answer 9

Occurs when an extracellular signalling molecule (e.g hormone) activates a specific receptor located on the cell surface or inside the cell. The receptor triggers a chain of events inside the cell, creating a response

Question 10

What do hydrophobic signals bind to and why

Answer 10

Hydrophobic signals can diffuse directly through the phospholipid bilayer of membranes. They therefore bind to intra cellular receptors

Question 11

Explain why hydrophobic signals are capable of diffusing through the plasma membrane (2)

Answer 11

• Hydrophobic signals can diffuse directly through the phospholipid bilayer of membranes. They therefore bind to intra cellular receptors
• they can do this because the tails of the phospholipids in the plasma membrane are also hydrophobic and allow the molecules to pass across

Question 12

What are the receptors for hydrophobic signalling molecules

Answer 12

The receptors for hydrophobic signalling molecules are transcription factors

Question 13

Describe what transcription factors are and their function

Answer 13

Transcription factors are proteins that when bound to DNA can either stimulate or inhibit initiation of transcription

Question 14

What can transcription factors do to binding of RNA polymerase

Answer 14

Transcription factors can enhance or block the binding of RNA polymerase to specific genes. Thereby controlling whether the gene is transcribed and therefore expressed

Question 15

Examples of hydrophobic signals are

Answer 15

• the thyroid hormone thyroxine
• steroid hormones such as oestrogen for testosterone

Question 16

What are receptor proteins for steroid hormones

Answer 16

The receptor proteins for steroid hormones are transcription factors

Question 17

What do steroid hormones form

Answer 17

Steroid hormones bind to specific receptors forming a hormone receptor complex

Question 18

Where are the receptors for steroid hormones

Answer 18

Steroid hormones bind to specific receptors in the cytosol or in the nucleus. The hormone receptor complex moves to the nucleus where it binds to specific sites on DNA

Question 19

What is a hormone response element (HRE)?

Answer 19

The hormone receptor complex moved to the nucleus where it binds to specific sites on DNA. The specific DNA sequences that the hormone receptor complex binds to are called hormone response elements

Question 20

What does binding at the HRE influence the rate of

Answer 20

Binding at these sites influence the rare of transcription, with each steroid hormone affecting the gene expression of many different genes

Question 21

Summary of the pathway of steroids (4)

Answer 21

• Steroid hormone passes through the plasma membrane into the nucleus
• the bromine binds to the receptor (transcription factor) forming a hormone- receptor complex
• the hormone - receptor complex binds to specific sites on DNA called hormone response elements (HREs)
• rate of transcription and gene expression is affected

Question 22

What is thyroxine

Answer 22

Thyroxine is a hydrophobic hormone produced by the thyroid gland. It is involved in regulating the Rate of metabolism.
As thyroxine is small and hydrophobic it is capable of diffusing through the phospholipid bilayer and binding an intracellular receptor

Question 23

What happens when thyroxine is not present

Answer 23

When thyroxine is not present it’s receptor protein is found in the nucleus bound to DNA. It sits on the DNA and inhibits the transcription of the gene for Na/K-ATPase (sodium potassium pump)

Question 24

Explain how the presence of thyroxine leads to the transcription of Na/K-ATPase (sodium - potassium pump)(2)

Answer 24

• when thyroxine binds it causes a conformational change in the receptor. This means the receptor protein can no longer bind the DNA and the gene is transcribed
• binding of thyroxine to its receptor leads to transcription of the gene for the sodium -potassium pump. This increases metabolic rate.

Question 25

Thyroxine is NOT present summary

Answer 25

- Thyroxine is not present - thyroid hormone receptor protein binds to DNA - transcription of Na/K-ATPase gene is inhibited - less Na/K-ATPase is transcribed - metabolic rate is reduced

Question 26

Thyroxine is present summary

Answer 26

- Thyroxine is present - thyroxine binds to thyroid hormone receptor - receptor undergoes a conformational change meaning it can no longer bind to DNA - gene for Na/K-ATPase is transcribed - metabolic rate increases

Question 27

Where do hydrophilic signalling molecules bind

Answer 27

Hydrophilic signalling molecules bind to transmembrane receptors and do not enter the cytosol

Question 28

Examples of hydrophilic signals are

Answer 28

- peptide hormones (eg insulin and ADH) - neurotransmitters (eg acetylcholine) This is because they are not capable of passing through the hydrophobic plasma membrane

Question 29

3 key steps of hydrophilic signalling

Answer 29

1 - reception - signalling molecule binds to transmembrane receptor 2 - transduction - signal is passed through the cell 3 - response - will vary depending on the signal

Question 30

When do transmembrane receptors change confirmation (2)

Answer 30

- Transmembrane receptors change conformation when the ligand binds to the extracellular face; the signal molecule does not enter the cell, but the signal is transduced across the plasma membrane - transmembrane receptors act as signal transducers by converting the extra cellular ligand binding event into intracellular signals, which alters the behaviour of the cell

Question 31

Transduced hydrophilic signals often involve

Answer 31

1. G proteins 2. Cascade of phosphorylation by kinase

Question 32

Describe the role of G-proteins transduction of an extracellular signal

Answer 32

G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels. Activated enzymes will then catalyse reactions within the cell. Ion channels will then either open or close to control ion movement

Question 33

Name the type of enzyme involved in the phosphorylation of a protein

Answer 33

Kinases

Question 34

Describe the role of phosphorylation cascades in the transduction of an extracellular signal

Answer 34

Phosphorylation cascades involve a series of events with one kinase activating the next in the sequence and so on. Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event

Question 35

How many pathways do phosphorylation cascades allow

Answer 35

Phosphorylation cascades allow more than one intracellular signalling pathway to be activated.

Question 36

Glucagon and Insulin

Answer 36

The levels of glucose in the blood must be controlled. There are two hormones involved in this: • insulin • glucagon

Question 37

What type of molecule is insulin?

Answer 37

insulin is a hydrophilic peptide hormone which promotes the conversion of excess glucose in the blood into glycogen for storage

Question 38

Describe the role of insulin in the body.

Answer 38

A rise in blood sugar level is detected by cells in the pancreas (islets of langerhans) which produce insulin. Insulin promotes the storage of excess glucose in various parts of the body such as the liver, fat tissue and muscle tissue

Question 39

Name three types of tissue which are affected by the action of insulin

Answer 39

- liver - fat tissue - muscle tissue

Question 40

How does glucose pass into cells

Answer 40

Glucose passes into cells by travelling through a transporter protein.

Question 41

Name the type of transporter protein.

Answer 41

GLUT4

Question 42

Name the type of transport bywhich glucose moves into cells.

Answer 42

facilitated diffusion

Question 43

The process which occurs when insulin binds to its receptor is as follows:

Answer 43

1. Insulin binds to its receptor 2. Receptor undergoes a conformational change that trigger’s phosphorylation of the receptor 3. À phosphorylation cascade is started inside the cell 4. Vesicles containing GLUT 4 are transported to the cell membrane 5. Glucose passes through the GLUT4 transporters

Question 44

Which types of tissue use GLUT4 transporters in the human body

Answer 44

GLUT 4 is a glucose transporter found only in fat/ muscle cells. In the liver it is a different glucose transporter which is recruited to the cell surface (GLUT 2/ GLUT1)

Question 45

Diabetes

Answer 45

if there is a failure in the process. the person suffers from diabetes mellitus There are two types: - Туре 1 - Type 2

Question 46

Describe the cause of Type 1 diabetes and how this is treated.

Answer 46

Type 1 diabetes is caused by a failure to produce insulin in the pancreas. It is Treated with regular insulin injections throughout the day

Question 47

Describe the cause of Type 2 diabetes and how this is treated.

Answer 47

Type II is caused by loss of insulin receptor function This therefore means that recmitment of GLUT 4 to the membrane fails.

Question 48

Why is exercise a form of treatment for Type 2 diabetes?

Answer 48

Type II diabetes is usually associated with obesity. Exercise also triggers the recruitment of GLUT4. so can improve uptake of glucose to fat and muscle cells in subjects with type 2 diabetes

Question 49

What difference do all cells have

Answer 49

All cells have an electrical potential difference (voltage) across their plasma membrane

Question 50

What is the membrane potential

Answer 50

This voltage is called the membrane potential. This is when there is a difference in electrical charge on the two sides of the membrane

Question 51

What is the resting potential

Answer 51

The membrane potential of a neuron that is not transmitting signals is called the resting potential.

Question 52

Describe the membrane potential of a neuron when at rest

Answer 52

The membrane potential of a neuron that is not transmitting signals is called the resting potential. Resting membrane potential is a state where there is no net flow of ions across the membrane

Question 53

What is a nerve transmission

Answer 53

The transmission of a nerve impulse requires changes in the membrane potential of the neurons plasma membrane. Nerve transmission is a wave of depolarisation of the resting potential of a neuron.

Question 54

Define the term polarisation

Answer 54

As the outside of the cell has an overall positive charge compared to the inside we say that the membrane is polarised

Question 55

What happens if the change in membrane potential is big enough

Answer 55

If the change in membrane potential is big enough it may trigger an action potential

Question 56

Define the term “action potential”

Answer 56

An action potential is a wave of electrical excitation along a neurons plasma membrane

Question 57

How do neurotransmitters initiate a response

Answer 57

Neurotransmitters initiate a response by binding to their receptors at a synapse

Question 58

What are neurotransmitter receptors

Answer 58

Neurotransmitter receptors are Ligand- gated ion channels

Question 59

What happens after the neurotransmitter has bound

Answer 59

After the neurotransmitter has bound to the receptor, a series of events occurs which results in depolarisation of the plasma membrane

Question 60

Define the term “depolarisation”

Answer 60

Depolarisation is a change in the membrane potential to a less negative value inside

Question 61

What happens to the wave of depolarisation after depolarisation of the plasma membrane

Answer 61

This wave of depolarisation will continue down the neuron, transmitting an electrical impulse

Question 62

When does the initiation of a nerve impulse begin

Answer 62

Initiation of a nerve impulse begins with binding of a neurotransmitter to a transmembrane receptor on the surface of the next neuron

Question 63

When is the opening of neighbouring voltage- gated sodium channels is triggered

Answer 63

If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of neighbouring voltage-gated sodium channels is triggered and sodium ions enter the cell down their electrochemical gradient

Question 64

Describe the effect of this rapid influx of sodium ions into the neuron

Answer 64

The influx of Na+ ions leads to a rapid and large change in the membrane potential. The wave of depolarisation which occurs along the neuron is called the action potential. A short time after opening, the sodium channels become inactivated

Question 65

What happens after the action potential reaches the end of the neuron

Answer 65

When the action potential reaches the end of the neuron it causes vesicles containing neurotransmitter to fuse with the membrane - this releases neurotransmitter ehuch stimulates a response in a connecting cell

Question 66

How is the resting potential of the membrane restored following a nerve impulse

Answer 66

To restore the membrane potential to a resting state, the sodium channels become inactivated. Voltage-gated potassium (K+) channels then open to allow potassium ions to move out of the cell

Question 67

What does the restoration of the resting membrane potential allows

Answer 67

restoration of the resting membrane potential allows the inactive voltage-gated sodium channels to return to a conformation that allows them to open again in response To another depolarisation of the membrane.

Question 68

Describe the role of the sodium potassium pump in restoration of the resting membrane potential

Answer 68

Following repolarisation the sodium and potassium ion concentration gradients are reduced. The sodium-potassium pump restores the sodium and potassium ions back to restoring potential levels and it re-establishes ion concentration gradients. It actively transports excess ions in and out of the cell

Question 69

Summary of the steps involved in a nerve transmission

Answer 69

1. Neurotransmitters initiate a response by binding to their receptors at a synapse 2. the neurotransmitter receptor is a ligand-gated Na+ channel so the binding cause the channel open and letting Na+ ions diffuse into the cell 3. Positively charged sodium ions move in. This causes the inside of the neuron to become less negatively charged 4. If sufficient Na+ ions enter the cell, it triggers the opening and neighbouring voltage -gated sodium channels and more Na+ ions enter the cell 5. A wave of depolarisation moves down the neuron called the action potential 6. A short time after opening, Na+ channels become inactivated 7. To restore the resting potential, voltage-gated potassium (K+) channels then open to allow potassium ions move out the cell 8. The sodium-potassium pump restores the sodium and potassium ions back to resting potential levels and it re establishes ion concentration gradients

Question 70

What does the retina area within the eye do

Answer 70

The retina is the area within the eye that detects light. It converts light into electrical signals.

Question 71

Animals have two types of photoreceptor cell in the retina

Answer 71

1. Rod cells 2. Cone cells

Question 72

Describe the function of rod cells in the retina

Answer 72

Rods function in dim light but do not allow colour perception.

Question 73

Describe the function of cone cells in the retina

Answer 73

Cones are responsible for colour vision and only function in bright light.

Question 74

Photoreceptors of the eye contain

Answer 74

- light sensitive molecule called RETINAL - membrane protein called OPSIN

Question 75

What is this name given to the retinal -opsin complex in rod cells?

Answer 75

In rod cells thus retinal - opsin complex is called RHODOPSIN

Question 76

Describe photoreceptors in cone cells

Answer 76

Cells different forms of opsin combine with retinal to give different photoreceptor proteins each with a maximal sensitivity to specific wavelengths of light (red, green, blue or UV)

Question 77

Describe the stages in the generation of a nerve impulse in response to light in rod cells

Answer 77

1. Retinal absorbs a photon of light and becomes photoexcited rhodopsin. Photo excited rhodopsin activates G- protein called transduction. A single photo excited rhodopsin activates hundreds of molecules of transducin 2. G- proteins (transducin) activate phosphodiesterase (PDE) each activated G-protein activates one molecule of PDE 3. PDE catalyses hydrolysis of cyclic GMP (cGMP)l each active PDE molecule breaks down thousands of cGMP molecules per second 4. Concentration of cGMP decreases causing a closure of ion channels in the membrane of rod cells. As no move Na+ ions enter cell, the membrane potential increases. Hyper polarisation of the membrane triggers nerve impulse in neurons in the retina