Biochem

Question 1

Glycogen is a combination of 2 things:

Answer 1

Glycogenin (core protein)

Multiple glucose molecules (bonded together in chains)

Question 2

In glycogen, glucose molecules are joined together by ———–

Answer 2

glycosidic bonds

Question 3

Glycosidic bonds can be:

——- forming straight chains OR ——– which allows branching

Answer 3

α 1-4 forming straight chains OR α 1-6 which allows branching

Question 4

What are the purpose of branches in glycogen?

Answer 4

To allow multiple points of breakdown as glycogen can only be broken down from the ends.

Question 5

2 forms of glycogen

Answer 5

Liver glycogen (storage system to maintain blood glucose between meals)
Muscles glycogen (source of energy to muscle tissue during exercise)

Question 6

Glycogenesis has an activated intermediate called ———–

Answer 6

UDP-glucose

best thought of an activated form of glucose in the same way ATP is activated phosphate

Question 7

Glycogenesis rate limiting enzyme

Answer 7

hexokinase

glucose&raquo_space; glucose-6-phosphate

Question 8

Glycogenesis enzymes

Answer 8

Hexokinase = rate-limiting enzyme (glucose&raquo_space; glucose-6-phosphate)
Glycogen synthase = α 1-4 (UDP-glucose&raquo_space; glycogen)
Transglycosylase = α 1-6 (UDP-glucose&raquo_space; glycogen)

Question 9

Gluconeogenesis

Answer 9

Production of glucose from a non glycogen source

e.g. amino acids, lactate and glycerol

Question 10

Gluconeogenesis is powered by ———–

Answer 10

oxidation of lipids

Question 11

The cori cycle

Answer 11

the process that recycles lactate formed by anaerobic respiration (lactate&raquo_space; pyruvate&raquo_space; glucose).
A TYPE OF GLUCONEOGENESIS

Question 12

The cori cycle occurs in the ———-

Answer 12

liver

Question 13

Lactate formation requires —– ATP

Cori cycle requires —– ATP

Answer 13

Lactate formation requires 2 ATP

Cori cycle requires 6 ATP - very energy insufficient

Question 14

glycogenolysis - reaction steps

Answer 14

Glycogen + Pi&raquo_space;> smaller glycogen + glucose-1-phosphate (this is immediately converted to glucose-6-phosphate)
In the liver, glucose-6-phosphate&raquo_space; glucose
In muscle, glucose-6-phosphate provides energy via glycolysis.

Question 15

Glycogenolysis rate limiting enzyme

Answer 15

glycogen phosphorylase

|&raquo_space; glucose-1-phosphate

Question 16

Lipids vs Triglycerides

Answer 16

Long chains mostly hydrocarbons vs 3 fatty acids + glycerol backbone

Question 17

Triglyceride function

Answer 17

Compact energy source (major storage form in adipose tissue)

Question 18

Lipids - 3 forms

Answer 18

Simple: fatty acids, waxes and triglycerols
Compound: phospholipid, glycolipids, lipoproteins
Steroids: cholesterol, hormones

Question 19

How do fats enter the mitochondria?

Answer 19

Lipids are converted to a usable form - Acetyl CoA.
Needs a carrier molecule to be transported = Acyl carnitine/Acyl CoA.
Transported via CARNITINE SHUTTLE

Question 20

Describe the carnitine shuttle

Answer 20

Carnitine + Acyl CoA&raquo_space;> Acyl carnitine
(Acyl carnitine is exchanged into cell through a translocase molecule - acyl carnitine transporter)
Acyl carnitine&raquo_space;> Carnitine + Acyl CoA
This replenishes Carnitine for the exchange with Acyl carnitine

Question 21

Breakdown of triglycerides (2 steps)

Answer 21

1) Forming Acyl-CoA = cytoplasm, needs CoA, 2ATP (fatty acid + CoA&raquo_space; Acyl CoA)
2) Β-oxidation = mitochondrial matrix, needs NAD, FAD2 + H2O - doesn’t need energy

Question 22

How many cycles of B-oxidation for C19?

Answer 22

8 cycles
19/2 = 9.5, round to 9, 9 - 1=8
(divided by 2, minus 1)

Question 23

Products of B-oxidation?

Answer 23

1 Acetyl CoA
1 FADH2
1 NADH + H+
1 fatty AcylCoA - 2 carbons
(at the end, 1 extra AcetylCoA or propionyl-CoA)

Question 24

Energy level of β-oxidation

Answer 24

Each acetyl-CoA makes 1 FADH2 , 3 NADH and 1GTP
FADH2 = 1.5ATP
NADH = 2.5ATP
GTP = 1 ATP

Question 25

Ketones are produced in ————

Used in ———-

Answer 25

Ketones are produced in the mitochondria of the liver

Diffuse out to the peripheries) and used in the heart and kidneys (converted back to Acetyl CoA

Question 26

Ketones can cause problems in ———

Answer 26

Starvation or diabetes
Oxaloacetate is used up for gluconeogenesis so ketones can’t be broken down.
Ketone levels rise, leading to acidosis (ketones = weak acids)

Question 27

Lipogenesis

Answer 27

de novo synthesis of fatty acids

Question 28

Lipogenesis location

Answer 28

mostly in the liver, kidneys, mammary glands, adipose tissue and the brain

Question 29

Lipogenesis occurs when ———

Answer 29

excess energy is consumed (mostly excess carbs)

Question 30

Lipogenesis is controlled by ——

Answer 30

Insulin - promotes storage
Glucagon - signals breakdown
Citrate - allosteric (lots of citrate promotes movement out of the mitochondria)

Question 31

Fatty acid synthesis =
In ———– cells starch is broken down&raquo_space; ————-
This is transported by ———- into the cytoplasm.
Then ———– is formed (a precursor for synthesis)

Answer 31

In hepatocytes, starch is broken down&raquo_space; acetyl CoA
This is transported by citrate into the cytoplasm.
Then Malonyl-CoA is formed (a precursor for synthesis)

Question 32

4 reactions of fatty acid synthesis

Answer 32

Condensation
Reduction
Dehydration
Reduction and release

Question 33

Malonyl-CoA is a ———-

It is formed from ———– by ————

Answer 33

Carbon doner formed from acetyl CoA by acetyl-CoA carboxylase

Question 34

In lipogenesis, a special acyl-carrier protein is used called ———–

Answer 34

ACP

Question 35

Fatty acids are synthesised by a cycle of reaction =

Answer 35

1) a starter chain is attached to ACP
2) acetyl-CoA + malonyl-CoA are used to add 2 C atoms per cycle; this consumes NADPH (e- donor)
* **extra enzymes exist to elongate the chain further or add unsaturated bonds

Question 36

Synthesis of triglycerides

Answer 36

Glycerol-3-phosphate (G-3-P) + 3 fatty acids form a triglyceride through esterification.

Question 37

G-3-P is formed from ————

Answer 37

1) glycerol in the liver

2) glucose in the adipose tissue

Question 38

Glycerol-3-phosphate

Answer 38

ACTIVATED glycerol

Question 39

What other products similar to triglycerides are also produced in the liver?

Answer 39

phospholipids, cholesterol and lipoproteins

Question 40

Break down of amino acids produces —– and ——— which are both are toxic

Answer 40

NH3 and NH4+

MUST BE EXCRETED AS BUILDUP IS DANGEROUS

Question 41

Amino acid absorption

Answer 41

1) Proteolytic enzymes in stomach/intestine produce single amino acids
2) Absorbed into intestinal cells
3) Released into blood

Question 42

Amino acid transamination

Answer 42

Moving the amino group from an amino acid to an alpha keto acid (happens in all tissues)

Question 43

Amino acid deamination

Answer 43

Conversion of amino groups to free ammonium ions

Question 44

Synthesis of urea location

Answer 44

mitochondrial matrix of hepatocytes

Question 45

Synthesis of urea purpose

Answer 45

a way of making the toxic NH4+ through less toxic products to urea that can be excreted

Question 46

Deamination of amino acids results in leftover ——–

Answer 46

carbon skeletons

Question 47

The carbon skeletons leftover from amino acid deamination have 2 fates:

Answer 47

1) conversion to glucose - glucogenic (degraded to pyruvate, which can go to glucose)
2) to be oxidised in the TCA cycle - ketogenic (degraded to acetyl-CoA and can form ketone bodies)

Question 48

The dangerous components of amino acids are excreted as which molecules?

Answer 48

Urea (80%, in the liver), uric acid, creatinine, NH4+

Question 49

The products of amino acid transamination are transported to the liver via two transport molecules =

Answer 49

alanine and glutamine