GI Biochemistry Flashcards
(115 cards)
1
Q
What is glycogenesis?
A
Synthesis of glycogen from glucose
2
Q
What is glycogenolysis?
A
Breakdown of glycogen to form glucose
3
Q
What is the difference in function between liver glycogen and muscle glycogen?
A
Liver glycogen is broken down between meals and releases glucose to maintain blood glucose levels for tissues such as red blood cells and the brain.
Muscle glycogen when broken down, can only be used in that muscle, not systemically. It is there to provide energy for the muscle between meals. It can then consume glucose by glycolois and generate ATP for bursts of physical activity.
4
Q
What is gluconeogenesis?
A
The synthesis of glucose from other, non carbohydrate products.
5
Q
When does gluconeogeneis occur?
A
When liver glycogen stores have been depleted (such as during the night)
6
Q
Describe the structure of glycogen
A
A polymer consisting of glucose molecules joined by alpha 1-4 glycosidic links. Branches are then introduced by alpha 1-6 glycosidic links
7
Q
By what reaction mechanism does glycogenolysis occur by?
A
Phosphorylisis
8
Q
What is glycogenin?
A
The protein that glycogen primer covalently attaches to
9
Q
Describe how synthesis of glycogen occurs?
A
Glucose can only be added to an existing glycogen chain (a glycogen primer containing at least 4 glucose residues in required) After this glycogen synthase adds glucose molecules onto the chain.
10
Q
Does more branching make the molecule more or less easy to breakdown.
A
Easier
11
Q
What must happen to glucose first in the process of glycogen synthesis and glycolysis?
A
Must be phosphorylysed to glucose 6 phosphate. This traps the glucose within the cell.
12
Q
Describe the process of glycogen synthesis:
A
- Glucose converted to glucose-6-phospahate (hexokinase)
- Glucose-6-phosphate concerted to glucose-1-phosphate (phosphglucomutase)
- Glucose 1 phosphate converted to UDP glucose (UDP glucose pyrophosphorylase)
- Glycogen synthase then adds on glucose molecules
13
Q
What kind of reaction is glucose to glucose 6 phosphate?
A
Phosphorylysis
14
Q
What is UDP glucose?
A
An activated form of glucose
15
Q
What happens to the UDP that is left over after glycogen has been made?
A
It is converted back to UTP, which can then renter the pathway to activate glucose. This costs 1 ATP molecule
16
Q
Foe each molecule of glucose that is added to glycogen, what is consumed?
A
1 ATP molecule
17
Q
What does UDP glucose stand for?
A
Uridone diphosphate glucose
18
Q
What is the structure of UDP glucose?
A
Auracil base, ribose sugar and two phosphates. The glucose is then attached to the glucose and this is what makes it active.
19
Q
What is the activated form of acetate?
A
Acetyl co A
20
Q
What is the activated form of phosphate?
A
ATP
21
Q
What do the phosphate ester linkages in a nucleotide sugar do?
A
Release free energy on hydrolysis.
22
Q
What is the rate limiting enzyme of glycogenesis?
A
Glycogen synthase
23
Q
What enzyme introduces beaches into the molecule?
A
Transglycosylase
24
Q
What enzyme catalyses glycogenolysis?
A
Glycogen phosphorylase
25
What happens in glyconeolysis?
One glucose molecule is cleaved of the ends of glycogen at a time. The glucose 1 phosphate is then converted to glucose 6 phosphate.
26
What is the difference between glucose 6 phosphate in the liver and glucose 6 phosphate in skeletal muscle?
In the liver it can be de phosphorylated and the resulting glucose released into the blood stream.
In skeletal muscle it cannot be de phosphorylated and has to be used to provide energy via glycolysis and the TCA cycle.
27
How is glucose transported in the blood?
Via a GLUT2 transporter
28
What stimuli increase the rate glycogen phosphorylase production?
Glucagon
Adrenaline
Cortisol
29
What hormone decrees the production of glycogen phosphorylase?
Insulin
30
What increases production of glycogen synthase?
Insulin
31
What decreases production of glycogen synthase?
Glucagon
32
What is the primary source of glucose overnight?
Gluconeogenesis
33
Give three precursors for gluconeogenesis
Lactate
Amino acids
Glycerol
34
How do we get lactate?
Synthesised by skeletal muscle under anaerobic conditions (Muscles convert pyruvate to lactate)
35
How do we get energy for gluconeogenesis?
From oxidation of fatty acids released from adipose tissue
36
Where does gluconeogeneis occur?
Mainly in the liver but also a small amount in the kidney
37
What three irreversible reactions occur in glycolysis and what are their enzymes?
1. Glucose to glucose 6 phosphat (hexokinase)
2. Glucose 6 phosphate to Fructose 6 phosphate (Phosphofructokinase)
3. Fructose 6 phosphate to Fructose 1,6 biphosphate (pyrivate kinase)
38
How many unique liver enzymes are required fro gluconeogenesis?
4
39
What is oxalacetate?
The first product of the first reaction starting from pyruvate. It is an intermediate in the TCA cycle.
It is found in the mitochondria
40
How is the unfavourable gluconeogeneis reaction allowed?
ATP hydrolysis
41
How may pyruvate molecules do you need to make one glucose molecule?
2
42
Wh do muscle produce lactate under times of anaerobic respiration?
To regenerate NAD+
43
Why can lactate be easily transported int he blood stream?
It is a polar molecule
44
What happens to the lactate produced in skeletal muscle, once it has been transported to the liver?
The liver regenerates it back to pyruvate then back to glucose where it can then be taken in the blood back to the tissues.
45
How many ATP does it cost for 1 lactate to be conveyed to glucose?
6
46
What is the benefit of gluconeogenesis occurring in the liver and delivering the glucose back to the tissues?
1. Neither tissue gets too acidic
| 2. Takes some of the burden away from the skeletal muscle for a while
47
What is the difference between glucogenic and ketogenic amino acids?
Glucogenic amino acids can be used as precursors for gluconeogeneis but ketogenic ones cannot be used for this purpose.
48
How can ketogenic amino acids enter the TCA cycle?
They are converted to acetyl coA and then can enter the TCA cycle only if ocaloacetate in present
49
In what two ways can glycogenic am into acids enter gluconeogenesis?
1. At a point in the cycle
2. Converted to pyruvate which either
- enters the cycle or
- is converted to acetyl coA which then enters the cycle if oxaloactetate is present
50
What is the first reaction in gluconeogenesis?
Pyruvate to oxaloacetate
51
At a systemic level, how are glycolysis and gluconeogenesis regulated?
Hormonal regulation by glucagon and insulin
52
What does glucagon signal in relation to gluconeogenisis and glycolysis?
A need for glucose.
| Therefore, it will stimulate gluconeogeneis and inhibit glycolysis
53
What does insulin signal in relation to gluconeogenisis and glycolysis?
That there is availability of glucose. Therefore, it will inhibit gluconeogeneis and stimulate glycolysis
54
What are enzymes regulated by in relation to gluconeogenisis and glycolysis?
Allosteric effectors
55
What does a High AMP or ADP signal and what does this cause at a cellular level.
Low energy in the cell. This inhibits gluconeogeneis in the cell as their is not enough energy to fuel this process.
56
What does high ATP in the cell cause?
Means there is high energy and so stops glycolysis and may possible stimulate gluconeogeneis if required.
57
what is fructose 2, 6 biphosphate?
An intermediate of glycolysis that is high in the fed state and low is the starved state. It will stimulate glycolysis at high levels.
58
What happens when citrate, alanine and acetyl coA levels in the cell are high?
These are all important precursors and so when presence is high it means pathways aren't being completed properly and so this indicated you need more energy. These therefore stimulate gluconeogenesis and inhibit glycolysis
59
What does increases fat intake without enough expenditure cause?
Increased numbers of adipocytes
| More fats in adipocytes
60
What is fat required for?
1. Energy source
2. essential fatty acids
3. Fat soluble vitamins
61
What is the main fat storage form in adipose tissue?
Triglycerides
62
What does alipathic mean?
No rings
63
What does polyunsaturated mean?
Several double bonds
64
What is the most common naturally occurring fatty acid?
Palmatic acid
65
What is an essential fatty acid?
One that cannot be synthesised by the body e.g. linoleum acid
66
How many carbon atoms does a fatty acid have to have before it is solid at rom temperature
8
67
Where are the products of fat digestion absorbed?
The mucosal cells of the intestine
68
What happens to short and medium length fatty acids?
They enter the portal blood
69
What happens to longer chain fatty acids after they have been absorbed by mucosal cells?
They are resynthesises into trigglycerides and incorporated into chylomicrons
70
What happens to chylomicrons at muscle and adipose tissue?
They are attached and cleaved by lipoprotein lipases into fatty acids where they can be:
1. Resynthesied to triglycerides to be stored in adipose tissue
2. Oxidised to provide energy
3. Dependant on amount available
71
What is lipolysis?
The breakdown of lipids
72
What causes the initial cleavage lipids?
Hormone sensitive lipases
73
What has to happen to fatty acids before the can be oxidised to convert energy?
The have to be converted to CoA derivatives.
| fatty acid + CoA------->> acyl CoA
74
Where does fatty acids conversion occur? How much energy does this require?
Cytoplasm
| 2ATP
75
Where does further oxidation of fatty acids occur?
Mitrochondrial matrix
76
Ho are acyl coA groups transported to the mitochondria
In the cytoplasm, fatty acids are transferred from acyl-CoA to carnitine. There is an acyl carnitine transporter in the inner membrane which facilitates transport of these into the mitochondria. In the matrix of the mitochondria the acyly group is removed and transferred out through the acyl canritine transporter.
77
Where does beta oxidation of fats occur?
Mitochondrial matrix
78
What are the products of each beta oxidation cycle?
1 acetyl coA
1 FADH2
1 NADH + H+
1 Fatty acyl - coA, shortened by 2 carbon atoms
79
How is glycerol broken down?
1. Activated to glycerol 3 phosphate by glycerol kinase
| 2. Dehydrogenated to dihydroxyacetone phosphate which is a normal intermediate of carbohydrate metabolism
80
How are ketone bodies formed?
Formed in the liver mitochondria from the acetyl coA from beta oxidation
81
What do ketone bodies do?
Diffuse into the blood stream and into peripheral tissues where they are important molecules of energy metabolism for the heart and kidney. Here they are converted to acetyl coA which then enters the TCA cycle.
82
What happens in diabetic ketosis?
1. Oxaloacetate is consumed for gluconeogeneis
2. Fatty acids are then oxidised to provide energy
3. Acetyl coA is converted to ketone bodies
4. High levels of ketones in blood
5. This is too much for extra hepatic tissue
6. accumulation leads to severe acidosis
7. This impairs tissue function particularly in the CNS
8. The smell of acetone can be detected in the breath.
83
What is lipogenesis?
Fatty acid synthesis
84
What happens when we taken in excess carbohydrates?
They are converted to fatty acids and triglycerides in the liver
Free fatty acids are transported in plasma bound to albumin
Triglycerides formed in the liver are transported to adipose tissue by VLDL for storage
85
What kind of process in lipogenesis?
Reductive. Electrons are required
86
What is the main organ for lipogenesis?
Liver
87
What is the series of events involved in converting carbohydrates into fat?
```
Starch
glucose
pyruvate
acetyl coA
Fatty acids
Triglycerides
```
88
Where exactly does the synthesis of fatty acids from acetyl coA occur?
The cytoplasm of liver cells
89
Where is acetyl coA generated?
The mitochondria (by pyruvate dehydrogenase complex)
90
How is citrate formed?
Condensation of acetyl with oxaloacetate (first step in the `TCA cycle)
91
How are acetyl groups transported into the cytoplasm?
Citrate. If there is increase in a acetyl coA there is an increase in citrate which cases movement.
92
Where is acetyl coA generated?
Mitochondrial matrix
93
Why is citrate needed to move acetyl coA?
Inner mitochondrial membrane is impermeable to it.
94
What is the vital first step in lipolysis?
The activation of acetyl coA to malonyl CoA by acetyl coA carboxylase
95
Where do you find acetyl coA carboxylase?
Liver and adipose tissue
96
What does malonyl coA do?
Donates carbon atoms to new lipid
97
What does fatty acid synthase do?
Catalyses synthesis of saturated long chain fatty acids from malonyl coA, acetyl coA and NADPH
98
What is the longest fatty acid length that can be created by fatty acid synthase?
16 carbons. Palmitic acid
99
What enzyme converts acetyl coA to malonyl coA?
Acetyl CoA carboxylae
100
What happens in terms of lipolysis if adrenaline is present?
Stops.
101
When is palmitoyal CoA expressed?
When fatty acids are in excess
102
Where is the major site of amino acid degradation?
Liver
103
What do amino acids contain that makes them different from the other digestive substances?
Nitrogen
104
What potentially toxic products does amino cid breakdown produce?
ammonia and ammonium ions
105
What is main molecule that is used to excrete nitrogen?
Urea
106
Name all the molecules used to excrete nitrogen
Urea
Uric acid
Creatinine
Ammonium ion
107
What are the three stages in the synthesis of urea?
1. Transamination (amino acid to leto acid)
2. De amination (ketoglutarate to glutamic acid as there is the removal of one amino group)
3. Urea cycle
108
Where does transamination occur?
Can occur in all tissues
109
Where does de amination occur?
Liver
110
What happens in the urea cycle?
ammonium's come from aspartic acid and a free ammonium and are converted to urea.
111
What happens in transamination?
Aminotransferases move the amino group from amino acids to keto acids to give glutamate.
112
How is glutamate transported to the liver?
Glutamate is transferred to pyruvate and gives alanine
| Or glutamine syntheses adds NH4 to glutamate giving glutamine.
113
What is alcaptonuria?
The degradation of phenylalanine and tyrosine is blocked
114
What is maple syrup urine disease?
The degradation of valine, isoleucine and leucine is blocked and the urine smells like maple syrup
There is also mental and physical retardation
Can be prevented by appropriate diet
115
What is phenylketonuria?
Phenylalanine accumulates in all body fluids and result in severe mental retardation.
Treated by a low phenylalanine diet.
