Biochemistry & metabolism

Question 1

Macronutrients=

Answer 1

Are a big group of specific molecules:
1. Carbohydrates
2. Lipids
3. Proteins

Question 2

Carbohydrates=

Answer 2

a group of molecules which include sugars and starches. They are made up chemically of carbon, hydrogen and oxygen atoms.
Carbohydrates are like building blocks of sugar. They are grouped by how many sugar units they have:
1. Monosaccharides (means one, smallest and simplest sugars)
2. Disacccharides (di means two, made by joining two blocks together)
3. Polysaccharides (poly means many, big chains of sugar blocks linked together)

Question 3

Lipids=

Answer 3

are insoluble in water.
Lipids are also made up of carbon, hydrogen and oxygen.
They include triglycerides, phospholipids, and steroids. The building blocks of lipids are Fatty acids and Glycerol

Question 4

Proteins=

Answer 4

Protein is the basic structural material of the body, accounting for 10-30% of cell mass, and they also make up enzymes, haemoglobin in blood, and the functional contractile proteins of muscle.
The building blocks of proteins are amino acids.

Question 5

Metabolism=

Answer 5

All biochemical reactions occurring in the body. We are extracting nutrients from the food that we’re consuming and we’re using this energy that is provided to drive numerous activities and body processes:
- Muscle contraction
- Nerve impulse conduction
- Active transport
- Digestion
- Biosynthesis
- Storage of nutrients
- Maintenance of body temperature etc
Metabolic pathways are either catabolic or anabolic.

Question 6

Catabolic Vs Anabolic pathways=

Answer 6

Catabolic:
- Break down complex molecules to simpler ones e.g., cellular respiration
- They are exothermic reactions because they release energy as heat + ATP
Anabolic:
- Build up of the complex molecules of life e.g., biosynthetic reactions (protein synthesis)
- They are endothermic reactions because they require energy input in the form of ATP

= all reactions are dependant on the actions of enzymes

Question 7

Stored ATP=

Answer 7

• ATP is stored in very small amounts in the body (80-100g).
• It is an immediate energy source & enough to supply energy for the first 2-6 seconds of physical activity.

Question 8

Catabolism of glucose has three linked metabolic pathways:

Answer 8

1. Glycolysis (‘anaerobic pathway’)
2. Krebs cycle
3. Electron transport chain (‘aerobic pathway’)

Question 9

Glycolysis=

Answer 9

• Glucose (6C) is broken down to 2 pyretic acid (3C) molecules in the cytoplasm
• Uses 2 ATP to ‘activate the glucose’ then forms 4 ATP through the pathway (net gain of 2 ATP)
• Intermediate metabolites are ‘oxidised’, hydrogens and their electrons are removed and picked up by a carrier NAD+ which is converted (reduced) to 2 NADH + H+

Question 10

What are the two possible outcomes of glycolysis?

Answer 10

1. If little oxygen is available pyruvic acid is converted to lactic acid. NADH + H+ converted back to NAD+ (anaerobic pathway)
2. If enough oxygen is available, pyruvic acid enters mitochondria for the Krebs cycle (aerobic pathway)
   Potential for production of 38 ATP per molecule of glucose

Question 11

Krebs cycle=

Answer 11

• Occurs in the mitochondria
• Involves building/ breaking bonds
• During the cycle, carbon atoms are removed as CO2 waste- this depends n acetyl-CoA entering the cycle

Question 12

Oxidation reactions=

Answer 12

Glycolysis and the Krebs cycle include oxidation reactions.
Oxidation= addition of oxygen, removal of hydrogens & removal of electrons

Question 13

When does catabolism of fats/ lipids happen and what are the effects?

Answer 13

When does it happen:
- Low CHO diet
- Starvation
- Uncontrolled diabetes mellitus
What are the effects:
- Kussmaul’s respiration= deep & fast
- Ketone breath= smells like pear
- Ketones in urine
- Eventually coma= death

Question 14

Catabolism of protein=

Answer 14

Used when other sources are unavailable (e.g., starvation) or during prolonged exercise (e.g., the end of a marathon).
1. In the liver, the amine group (NH2) is removed from amino acids= deamination.
- Amine group converted to ammonia (NH3) then to urea (excreted in urine).
2. Remaining part of molecules may be converted to pyruvic acid or Acetyl-CoA.
- Carry on to the Kreb’s cycle

Question 15

Cellular respiration=

Answer 15

Series of metabolic reactions that convert stored energy in nutrients (food) into usable energy- ATP- for biological processes

Question 16

Glycogenesis =

Answer 16

• Glucose molecules are linked together in long chains to form glycogen
• It occurs in absorptive state (when blood glucose levels are surplus to energy requirements)
• Can only happen in presence of insulin

Question 17

Glycogenolysis=

Answer 17

• Is glycogen splitting, happens in stressful situations
• Happens in the post-absorptive state
• Influenced by glucagon, epinephrine and cortisol

Question 18

Gluconeogenesis=

Answer 18

The creation of new glucose from other non CHO (carbohydrate) sources through:
1. lactic acid= by product of anaerobic glycolysis
2. Glycerol= from lipolysis or digestion of dietary fats & oils
3. Amino acids= from dietary protein or body protein stores
So, provides glucose when dietary intake is insufficient or absent.

Question 19

Lipogenesis=

Answer 19

• Storing fat in absorptive state
• Is multiple pathways whereby ingested glucose, FAs and AAs are converted to fat
• Influenced by the presence of insulin

Question 20

Lipolysis=

Answer 20

• In post absorptive state
• Stored triglycerides in adipose are broken down to Glycerol & FAs.
  Fatty acids:
• Can be used for energy in most cells (β-oxidation; Krebs; ETC).

Glycerol:
- Can be converted to Pyruvic Acid for ATP production (Krebs; ETC).
- Or undergo gluconeogenesis (liver) for maintaining blood glucose.
Influenced by Glucagon; Epinephrine; Cortisol; Thyroid hormones.

Question 21

Ketoacids=

Answer 21

1. May enter Kreb’s cycle and be fully catabolised for energy.
2. May be converted to glucose.
3. May be converted to fat.