Biochemistry

Question 1

Define euglycemia

Answer 1

normal concentration of glucose in the blood

Question 2

What cells produce insulin?

Answer 2

Beta cells

Question 3

Where are beta cells found

Answer 3

Pancreatic islets in the endocrine pancreas

Question 4

Name the four different types of pancreatic islets cells and what they secrete

Answer 4

Beta cells - insulin Alpha cells - glucagon Delta cells - somatostatin Polypeptide cells - pancreatic polypeptide

Question 5

Where is the insulin precursor synthesised?

Answer 5

rough endoplasmic reticulum

Question 6

What other peptide is secreted with insulin, what is its function?

Answer 6

C-peptide, has no metabolic function

Question 7

Describe the structure of insulin

Answer 7

Two polypeptide chains (alpha and beta) bound together by disulphide bonds

Question 8

What do the disulphide bonds create?

Answer 8

3D structure which allows binding to receptors

Question 9

Name the channel that glucose moves through to enter the beta cell

Answer 9

GLUT 2

Question 10

What does glucose entry to the beta cell result in? What is the product?

Answer 10

Phosphorylation by glucokinase resulting in the production of 36ATP per glucose molecule

Question 11

What is the purpose of the ATP produced during glycolysis in the beta cell?

Answer 11

It inhibits the ATP sensitive potassium channel preventing potassium from leaving the cell leading to depolarisation

Question 12

Describe the beta cell response to depolarisation

Answer 12

Opening of voltage gated calcium channels stimulates insulin vesicles binding to the membrane and as a result insulin release

Question 13

Explain the two phases of insulin release

Answer 13

1st phase - insulin is ready to go (readily releasable pool) 2nd phase - vesicles still need some manipulation (preparatory reactions) to become mobilised & available

Question 14

What are the two subunits of the KATP channel?

Answer 14

• inward rectifier pore subunit (KIR) - sulphonylurea regulatory subunit (SUR1)

Question 15

Name two chemicals that inhibit KATP channels

Answer 15

• ATP - Sulphonylurea

Question 16

Name one chemical that stimulates KATP channels

Answer 16

• diazoxide

Question 17

What shape is the KATP channel?

Answer 17

Octomeric

Question 18

When insulin in present, name six processes that increase

Answer 18

amino acid uptake DNA & Protein synthesis

Growth responses

Glucose uptake

Lipogenesis

Glycogen synthesis

(Gene expression)

Question 19

When insulin is present, name two processes that decrease

Answer 19

lipolysis gluconeogenesis (gene expression)

Question 20

What type of receptor does insulin bind to?

Answer 20

Receptor tyrosin kinases (alpha unit)

Question 21

After insulin binding what happens to the receptor?

Answer 21

beta subunits dimerise & phosphorylate activating catalytic receptor activity

Question 22

What is autocrine regulation?

Answer 22

chemicals released from he cells bind to receptors on/in the cell that is releasing them

Question 23

What is paracrine regulation?

Answer 23

chemical released from the cell binds to receptors on adjacent cells

Question 24

What is endocrine regulation?

Answer 24

chemicals released from the secretory cells are transported via the circulatory system to target cells

Question 25

Describe negative feedback

Answer 25

product inhibits a intermediate pathway in order to maintain homeostasis and oppose change

Question 26

Describe positive feedback

Answer 26

initial stimulus produces a response that exaggerates the change

Question 27

Name two general regulatory mechanisms of homeostasis

Answer 27

Intrinsic - autocrine & paracrine Extrinsic - nervous system & endocrine

Question 28

How does negative feedback control the hypothalamic pituitary adrenal axis?

Answer 28

Elevated cortisol inhibits intermediate steps to prevent more being produced

Question 29

What is the purpose of cortisol?

Answer 29

- stimulate gluconeogenesis - protein breakdown & liberation of free fatty acids - immune system suppression - stress response - blood pressure maintenance

Question 30

Define hormones

Answer 30

any substance elaborated by one cell to regulate another cell

Question 31

How does the hypothalamus integrate nervous & endocrine systems?

Answer 31

* secretion of regulatory hormones * synthesis of hormones * direct neural control (secretion of adrenaline & noradrenaline from adrenal medulla)

Question 32

Describe diurnal control

Answer 32

(curcaduab rhythm) External cues (light/dark) evoke fluctuations in hormone secretions. Levels are also influenced by the rate at which hormones are eliminated by the body

Question 33

State three classes of hormones

Answer 33

* Steroids * Amines * Peptide & protein hormones

Question 34

Where are steroids derived from and how are they transported?

Answer 34

Lipids derived from cholesterol, secreted not stored transported in the blood bound to carrier proteins

Question 35

Give examples of two steroids and where they are secreted from

Answer 35

* cortisol - adrenal cortex involved in stress * testosterone & oestradiol - secreted from gonads involved in sexual characteristics

Question 36

Describe the mechanism of action of steroids

Answer 36

Bind to receptors & enter the nucleus (forming a complex), this binds to DNA & activates specific gens leading to the production of key proteins

Question 37

What are amines derived from & where are they secreted?

Answer 37

Amino acids, secreted from the thyroid & adrenal medulla

Question 38

How are amines transported in the blood?

Answer 38

Catecholamines - hydrophilic & transported free in the blood Thyroid - bound to carrier proteins

Question 39

How do amines work?

Answer 39

Bind to receptors on the cell membrane to stimulate cellular responses

Question 40

What is the difference between peptide and protein hormones?

Answer 40

peptide - short chains protein - larger molecules

Question 41

What is peptide/protein hormones polarity and how are they transported?

Answer 41

Hydophilic & transported 'free' in blood plasma

Question 42

How are peptide/protein hormones synthesised?

Answer 42

As precursor molecules, stored in vesicles and different end hormones are made by cleaving a common precursor using different enzymes

Question 43

Where are peptide & protein hormones secrected from?

Answer 43

- pituitary - parathyroid - heart - stomach - liver - kidneys

Question 44

What do carrier protiens allow?

Answer 44

1. Facilitation of hormone transport 2. Increased half-life of hormone 3. A reservoir for the hormone

Question 45

Name three important carrier proteins and what they carry

Answer 45

* cortisol binding globulin (cortisol & aldosterone) * thyroxine binding globulin (thyroxine T4 & some T3) * sex steroid binding globulin (testosterone & oestradiol)