Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

BS - Gastrointestinal System pt.1 > Post-absorption Processing of Carbohydrates > Flashcards

Post-absorption Processing of Carbohydrates Flashcards

1
Q

Which 3 sugars are absorbed from the GI tract?

A
  1. glucose
  2. galactose
  3. fructose
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where do glucose and fructose come from?

A

Glucose comes from starch and glycogen breakdown (animal products)

Fructose comes from sucrose (sugar)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Where does galactose come from?

A

Galactose is one of the monomers of lactose

Lactose comes from dairy products

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Which metabolic pathway will fructose and galactose enter?

A

They are converted to compounds that will enter the same metabolic pathway as glucose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the 2 potential products with galactose and fructose metabolism?

How common are they?

A
  1. hereditary fructose intolerance occurs in 1 in 20,000 births
  2. galactosaemia occurs in 1 in 23,000 births

They are genetically inherited and are associated with an absence of enzymes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the 4 possible fates of glucose?

A
  1. metabolism to produce energy (ATP)
  2. conversion to glycogen for storage
  3. synthesis of other cellular components
  4. conversion to fat for storage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the other cellular components that glucose may be converted to?

A

It can be converted into ribose phosphate, which is used to make DNA and RNA

It can be converted into glycoproteins and glycolipids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Where will glucose be stored as glycogen after a meal?

A

In the liver and skeletal muscle

Some glucose is also stored as fat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

At what concentration should blood glucose be maintained at and why?

A

Maintaining blood glucose at around 5 mM is crucial for survival

This is because the brain relies on glucose for ATP synthesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens if blood glucose falls below 3 mM?

A

This leads to confusion and coma

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens if blood glucose rises above 8 mM?

Why does this occur?

A

It leads to long term vascular damage

Damage to the vascular system occurs through protein glycation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What must glucose be converted to before it can be used to produce energy?

A

Glucose and fatty acids are converted to acetyl CoA

Glucose must be first converted to pyruvate, then acetyl CoA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What happens once glucose (and fatty acids) are converted to acetyl CoA?

A
  1. Acetyl CoA enters the Krebs cycle
  2. The Krebs cycle produces reduced coenzymes (e.g. NADH)
  3. NADH carries high energy electrons to the IMM and passes them to the electron transport chain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why is glucose a universal metabolic fuel?

A

It is used by all cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Where does glycolysis take place?

What is significant about when glycolysis can generate ATP?

A

It takes place in the cytosol of ALL cells

Glycolysis can generate ATP in the presence or absence of oxygen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the 2 phases of glycolysis?

A
  1. preparative phase

2. generating phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does the preparative phase require?

Where does it run to?

A

It requires ATP

It runs from glucose to the generation of fructose 1,6-bisphosphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Where does the generating phase run to?

What does it generate?

A

It runs from fructose 1,6-bisphosphate to pyruvate

It generates ATP and NADH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the overall equation for glycolysis?

A

glucose + 2 ADP + 2 Pi + 2 ATP + 2 NAD+

————>

2 pyruvate + 2 NADH + 4ATP + 2 H+ + 2 H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How many molecules of ATP are produced per molecule of glucose during glycolysis?

A

4 molecules of ATP are generated per glucose molecule

2 ATP are consumed during the preparative phase

The net production is 2 ATP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Under anaerobic conditions, how much ATP is generated per glucose molecule?

What is this process?

A

2 molecules of ATP are generated per molecule of glucose via glycolysis

This process is substrate level phosphorylation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Under aerobic conditions, how many molecules of ATP are generated per glucose and why?

A

Under aerobic conditions, ATP is used to generate a further 3-5 molecules of ATP through oxidative phosphorylation

Aerobic glycolysis generates 5-7 ATP molecules per glucose molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How many molecules of ATP are produced per glucose molecule after complete oxidation of glucose via the Krebs cycle?

A

This yields 30 - 32 molecules of ATP per glucose molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the first reaction in glycolysis which requires ATP?

Why is this reaction important?

A

Conversion of glucose to glucose-6-phosphate

This involves hexokinase and glucokinase

It prevents glucose from leaving the cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What is the second reaction in glycolysis which requires ATP? Which enzymes are involved?
Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate This involves phosphofructokinase-1
26
What is significant about the ATP-requiring reactions in glycolysis?
Most reactions in glycolysis are reversible These reactions are IRREVERSIBLE so allow for control of the pathway
27
What are the 3 key control points in glycolysis?
1. Hexokinase/glucose 2. Phosphofructokinase-1 3. Pyruvate kinase
28
Why does the hexokinase/glucose stage act as a control point in glycolysis?
It converts glucose to glucose-6-phosphate so it is only performed when it is needed
29
Why is phosphofructokinase-1 the main control step of glycolysis?
It involves splitting a 6 carbon molecule into 2 3-carbon units This is the start of the generating phase
30
Why does the generating phase run twice per molecule of glucose?
Each 3 carbon unit produced by phosphofructokinase enters the generating phase Per glucose molecule, 2 3C units are produced
31
What is involved in the pyruvate kinase control step?
This converts phosphoenolpyruvate into pyruvate It generates 1 ATP
32
What is the other reaction in the generating phase that generates a molecule of ATP?
Conversion of 1,3-bisphosphoglycerate into 3-phosphoglycerate This is catalysed by phosphoglycerate kinase
33
What happens to pyruvate in the absence of oxygen?
It is NOT converted to acetyl CoA to enter the Krebs cycle It is converted to lactate and NAD+ is regenerated
34
During the process of converting pyruvate to lactate, how much ATP is produced?
2 molecules of ATP are produced per molecule of glucose
35
Why is the conversion of pyruvate to lactate important for maintaining the rate of glycolysis?
It prevents the build-up of pyruvate at the end of the metabolic pathway by removing it Build-up of pyruvate would slow down glycolysis
36
Why is the conversion of pyruvate to lactate important in maintaining NAD+ levels?
There is a requirement to regenerate NAD+ If NADH builds up, NAD+ levels fall This also leads to a slowing down of glycolysis
37
What is meant by the Warburg effect?
High lactate production under aerobic conditions can be diagnostic of cancer
38
What type of glycolysis is used by tumour cells?
Tumour cells absorb glucose more rapidly than normal cells They use anaerobic glycolysis in preference to oxidative phosphorylation, even in the presence of oxygen
39
Why do tumour cells use anaerobic glycolysis?
It aids the growth of the tumour in the absence of a good blood supply As the tumour grows, it outstrips its own blood supply and it takes time for new blood vessels to grow
40
What type of scan can be used to identify tumours? How does this work?
Positron emission tomography (PET) scans using 2-18F-deoxyglucose It does this by identifying the increased glucose uptake and glycolysis of the tumour
41
What can glucose be converted into for storage?
1. glycogen | 2. fatty acids which are then converted into lipids
42
Where is glycogen found in the body?
Every cell contains a small amount of glycogen It is mainly found in the liver and skeletal muscle
43
What is the structure of glycogen and what types of linkages does it contain?
It has a branched structure a-1,4 linkages form the main body of the molecule a-1,6 linkages form the branch points
44
Why is the branched structure of glycogen beneficial?
The branched effect allows glucose to be rapidly added to glycogen, and rapidly released when it is needed
45
What is the role of glycogen within the liver? How does it achieve this?
The role of glycogen is to maintain blood glucose levels Glycogen is broken down in the liver to release glucose into the bloodstream
46
How do glycogen levels in the liver fluctuate?
Glycogen levels fluctuate a lot Liver glycogen levels are particularly low in the morning before food is consumed - this can lead to fainting
47
What is the first stage in glycogen synthesis? What enzyme is required?
glucose-6-phosphate is converted to glucose-1-phosphate This is performed by phosphoglucomutase
48
What happens to the glucose-1-phosphate that is formed in glycogen synthesis?
UTP and glucose-1-phosphate come together to form UDP-glucose and phosphate UDP acts as a carrier
49
What is the role of UDP in glycogen synthesis?
UDP transfers glucose-1-phosphate to glycogenin Glycogenin attaches to the hydroxyl group of a tyrosine residue
50
What factor limits the amount of glycogen that can be stored?
The amount of glycogenin present limits storage of glycogen
51
What happens once glucose-1-phosphate has joined to glycogenin?
The glycogen chain is elongated and branch points are added The key control enzyme is glycogen synthase
52
What is glycogenolysis?
The breakdown of glycogen
53
What is the enzyme involved in the first stage of glycogenolysis? What does it do?
Glycogen phosphorylase removes glucose units from glycogen The glucose-1-phosphate is then converted to glucose-6-phosphate
54
Where will the glucose-6-phosphate be converted to glucose during glycogenolysis?
The glucose-6-phosphate is only converted to glucose in the liver and kidneys This is due to the presence of the necessary enzyme
55
What happens to the glucose-6-phosphate produced in glycogenolysis in muscles?
In muscle cells, the glucose-6-phosphate goes straight into glycolysis
56
What are the 2 main effects of athletic training on muscles?
1. increased numbers of mitochondria allow for more aerobic respiration 2. increased muscle glycogen content
57
What type of energy do long-distance runners rely on? What is "glycogen loading"?
They rely on fat metabolism for energy, but the 'final push' at the end requires glycogen "glycogen loading" involves eating high carbohydrate diets in preparation for racing to increase glycogen stores
58
Why do long distance runners often collapse?
Exhaustion and collapse are caused by the depletion of glycogen The muscles have run out of energy
59
What happens once glycogen storage is saturated?
Glucose can be broken down into acetyl CoA, which is converted to fatty acids
60
What will fatty acids be converted to for storage?
Fatty acids are converted to triacylglycerols for storage
61
In which cells does fatty acid synthesis occur?
It occurs in the cell cytosol of: 1. mainly in the liver 2. in adipose tissue 3. in breast tissue during lactation
62
What happens to acetyl CoA produced from glucose?
It cannot get out of the mitochondria High levels of acetyl CoA in the mitochondria leads to the synthesis of citrate
63
What happens to citrate that is formed when there are high levels of acetyl CoA in the mitochondria?
1. Acetyl CoA carboxylase adds carbon dioxide to citrate This produces malonyl CoA (3C molecule) 2. This reaction is repeated many times, adding 2 carbons each time, until palmitate is produced
64
What is palmitate? What happens once palmitate is formed?
Palmitate is a 16 carbon molecule From palmitate, double bonds can be inserted into the chain and longer-chain fatty acids can be made
65
How can weight be gained from a low-fat diet?
If more sugar is taken in than required, this leads to the synthesis of fat This process results in palmitate and longer chain fatty acids
66
Where does triacylglycerol synthesis occur? What is involved in this process?
Occurs in the endoplasmic reticulum This involves the addition of 3 fatty acids to a molecule of glycerol-3-phosphate
67
Where are triacylglycerols stored? What happens to triacylglycerols in the liver?
They are stored in the cytosol of adipose tissue In the liver, they are packaged to form VLDL, which is secreted into the blood
68
Where are the VLDLs produced in the liver transported to?
1. adipose tissue for storage | 2. other peripheral tissues for use as an energy source
69
What are the 2 main reasons why control of metabolism is needed?
It is needed to ensure that cells and the whole body can: 1. work efficiently to utilise the materials it has to create the metabolites it needs 2. adapt to different conditions
70
How does control of metabolism occur within the cell?
Cells respond to energy availability and the need for specific metabolites
71
How does control of metabolism occur on a whole body level?
hormonal signalling allows the body to adapt to the environment
72
What is meant by product inhibition as a way of controlling reaction rates?
If an enzyme is producing a lot of a product which is not being used, this will slow the reaction rate
73
How may covalent modification affect reaction rate?
Covalent modification can activate or inhibit an enzyme through the addition or removal of phosphate groups
74
How may hormones affect reaction rate?
Some hormones control the amount of enzyme that is present through controlling the rate of synthesis or degradation
75
Why are ATP levels not used to monitor energy status/ What is used instead?
ATP levels fluctuate quite quickly as it is constantly being produced and broken down Levels of AMP are a sensitive monitor of energy status
76
What is the role of AMP-activated protein kinase?
It phosphorylates key enzymes involved in energy metabolism in the heart, adipose tissue, liver and muscle
77
What are the overall effects of AMP-activated protein kinase?
1. it increases energy-providing pathways | 2. it inhibits anabolic/synthetic pathways
78
What happens to levels of insulin after eating? What is the result of this?
Levels of insulin are raised after eating Transporters for glucose are moved into the membrane of the muscle, allowing more glucose to enter the cell
79
What will hexokinase be inhibited by?
It is inhibited by product inhibition The retention of glucose-6-phosphate inhibits hexokinase
80
What controls the rate of glycogen synthesis and break down?
Phosphorylation Phosphorylating glycogen phosphorylase speeds up glycogen breakdown Phosphorylating glycogen synthase slows it down so there is less glycogen synthesis
81
What does high glucagon levels lead to?
high glycogen means that blood glucose levels are low this leads to the breakdown of glycogen to release glucose
82
Why will high ATP inhibit the breakdown of glucose?
It signals that no more ATP is needed
83
How do energy levels influence the synthesis of fatty acids from glucose?
Low energy levels inhibit fatty acid synthesis from glucose This is activated by the presence of insulin When there is lots of food, excess energy will be stored
84
what is the role of insulin?
1. increases expression of genes which code for enzymes of glycolysis 2. decreases expression of genes which code for enzymes of gluconeogenesis
85
What is gluconeogenesis?
The process of making new glucose
86
What will high levels of insulin stimulate?
Glycolysis
87
What is signalled by high levels of glucagon?
A lack of energy
88
What is the role of glucagon?
It regulates the level of fructose-2,6-bisphosphate This will activate glycolysis and inhibit gluconeogenesis
89
What happens when glucagon levels are high?
High glucagon will phosphorylate an enzyme, leading to degradation of fructose-2,6-bisphosphate This decreases glycolysis
90
What happens when glucagon levels are low?
Low glucagon dephosphorylates an enzyme, leading to synthesis of fructose-2,6-bisphosphate This increases glycolysis

BS - Gastrointestinal System pt.1 (22 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions