Lipids, membranes, metabolism

Question 1

Compare a soap bubble with a cell membrane:

Answer 1

• Both have a hydrophilic head that attracts water and a hydrophobic tail which repels water
• Soap bubble has tail pointing out
• Lipid vesicles have tail pointing in

Question 2

How cholesterol is a bidirectional regulator of membrane fluidity…

Answer 2

Adds strength
At high temps - stabilises membrane and raises its melting point
At low temps - prevents phospholipids from clustering together and stiffening

Question 3

Catabolic =

Answer 3

Breakdown of complex molecule to produce energy using oxidation

Question 4

Anabolic =

Answer 4

Formation of complex molecules from simple ones utilising energy, using reduction

Question 5

Exergonic =

Answer 5

Reactions are spontaneous and release energy

DG = negative

Question 6

Endergonic =

Answer 6

Reactions are non-spontaneous and require energy to occur

DG = positive

Question 7

Energy of a reaction:

Answer 7

DG = DH -TDS

Gibbs free energy change of reaction =
Heat exchange with surroundings - (temperature in K x measure of disorder)

Question 8

Measure of disorder (S)…Increase=

Decrease=

Answer 8

Increase in disorder = positive DS

Decrease in disorder = negative DS

Question 9

Heat exchange with surroundings (H)…
Heat released=
Heat absorbed=

Answer 9

Heat released = exothermic = negative DH

Heat absorbed = endothermic = positive DH

Question 10

Standard conditions -

Answer 10

1M concentrations
25 degrees Celsius
PH 7

Question 11

Energy broken down from food is used for…

Answer 11

Synthetic processes
Mechanical work
Active transport

Question 12

Sources of energy -

Answer 12

Carbohydrates
Lipids
Proteins

Question 13

ATP =

Answer 13

Adenosine triphosphate
Energy currency
Contains an adenine base, a ribose sugar and 3 phosphate groups

Question 14

The hydrolysis of phosphoanhydride bonds in ATP release energy because…

Answer 14

Resonance stabilisation of orthophosphate favours ATP hydrolysis
Electrostatic repulsion created by 4 negative charges, is reduced when ATP is hydrolysed
Stabilisation due to hydration, water binds more effectively to ADP and Pi

Question 15

Carrier molecules =

Answer 15

Small molecules that have important roles in passing electrons

E.g. NAD+, NADP, FAD, FMN

Question 16

During catabolic processes…

Answer 16

Intermediates are oxidised and coenzyme (NAD) is reduced, ATP is produced when NADH is reoxidised in oxidative phosphorylation

Question 17

During anabolic processes…

Answer 17

Intermediates are reduced and coenzyme is oxidised

Question 18

Catabolism: stage 1 -

Answer 18

• extracellular
• building block molecules absorbed into circulation
• no energy produced

Question 19

Catabolism: stage 2 -

Answer 19

• many pathways
• intracellular
• building block molecules are even simpler molecules
• oxidative

Question 20

Catabolism: stage 3-

Answer 20

• mitochondrial
• a single pathway - citric acid cycle
• oxidative
• acetyl precursors for biosynthesis
• oxidative phosphorylation
• NADH + FAD2H reoxidised
• O2 required (reduced to H2O

Question 21

Carbohydrates:

Answer 21

General formula = (CH2O)n

Contain aldehyde or ketone groups
Multiple -OH groups
Monosaccharide - Single sugar units

Monosaccharides are linked by alpha - 1,4 - glycosidic bonds to form complex carbohydrates

Question 22

Maltose =

Answer 22

Glucose + glucose

Question 23

Lactose =

Answer 23

Galactose + glucose

Question 24

Sucrose =

Answer 24

Fructose + glucose

Question 25

Glycogen

Answer 25

Alpha - 1,4 and alpha -1,6 glycosidic bonds Highly branched Storage in animal cells

Question 26

Cellulose

Answer 26

Beta -1,4-glycosidic bonds only Unbranched Plants cell wall

Question 27

Starch

Answer 27

Alpha-1,4 and alpha-1,6 glycosidic bonds Less branched Plant storage molecule

Question 28

Glycolysis :

Answer 28

- central pathway of sugar metabolism - present in all cell types - takes place in the cytoplasm

Question 29

Glycolysis step 1

Answer 29

Input of some energy | ATP used to phosphorylate intermediates

Question 30

Glycolysis stage 2

Answer 30

Carbon-6 converted to 2x carbon-3 ATP produced NADH produced

Question 31

Substrate level phosphorylation =

Answer 31

Direct formation of ATP by transfer of phosphate group from 1,3-bisphosphoglycerate to ADP

Question 32

Glycolysis under aerobic conditions…

Answer 32

- pyruvate further oxidised in citric acid cycle - NADH used to form ATP in oxidative phosphorylation - NAD+ regenerated to allow glycolysis to continue

Question 33

Glycolysis under anaerobic conditions…

Answer 33

- stage 3 of catabolism does not occur - NADH would not be oxidised - glycolysis stops due to lack of NAD+ - no ATP produced

Question 34

Glycolysis In yeast…

Answer 34

Conversion of pyruvate to ethanol by pyruvate decarboxylase and alcohol dehydrogenase allows the oxidation of NADH to NAD+

Question 35

Glycolysis in mammals…

Answer 35

When the supply of oxygen is inadequate and cells without mitochondria Pyruvate converted to lactate by lactate dehydrogenase

Question 36

The pentose phosphate pathway -

Answer 36

Phase 1: - oxidative - irreversible - produces NADPH, CO2, 5-carbon sugars Phase 2: - nonoxidative - reversible - produces 3 carbon sugars

Question 37

Lipids :

Answer 37

- insoluble in water | - contain C,H,O (phospholipids contain P,N)

Question 38

Triacylglycerols…

Answer 38

Storage lipids | Made up of 3 fatty acids and glycerol

Question 39

Dietary lipids -

Answer 39

- Lipids are emulsified in the small intestine - digestion of lipids by lipase - absorption by intestinal mucosal cell - transportation to tissues

Question 40

Fatty acid catabolism (beta-oxidation)…

Answer 40

- Occurs in mitochondria - Fatty acid cycles through sequence of reactions - 2 carbon removed at each cycle - 1 NADH and 1 FAD2H produced in each cycle - all intermediate linked to coenzyme A

Question 41

Steps of fatty acid catabolism :

Answer 41

1) Activation of fatty acids by linkage to coenzyme A 2) Transport of fatty Adly CoA into mitochondria by translocase protein 3) Oxidation of fatty acyl CoA

Question 42

Dietary proteins …

Answer 42

- dietary proteins digested in the stomach by proteases - further digestion in The lumen of the intestine by peptidases - transport into intestinal cells and into blood

Question 43

Degradation of amino acids…

Answer 43

Step 1 -transfer of amino groups to alpha-ketoglutarate Step 2 -dehydrogenation to produce ammonium ion

Question 44

Urea cycle: removal of ammonium ion

Answer 44

Toxic NH4+ is converted to urea and excreted

Question 45

When nitrogen balance is positive -

Answer 45

Intake of nitrogen (protein) > loss …during active growth, pregnancy, tissue repair

Question 46

When nitrogen balance Is negative -

Answer 46

Intake of nitrogen (protein) < loss …during starvation

Question 47

Citric acid cycle…

Answer 47

- Removes electrons from acetyl CoA to form NADH and FADH2 | - reoxidation of NADH and FADH2in oxidative phosphorylation produces ATP

Question 48

Link between glycolysis and citric acid cycle =

Answer 48

Pyruvate dehydrogenase | = catalysed formation of Acetyl CoA from pyruvate

Question 49

Regulation of citric acid cycle includes:

Answer 49

- ATP/ADP ratio - NAD+/NADH ratio - allosteric regulation - product inhibition - substrate availability

Question 50

The citric cycle is amphibolic =

Answer 50

Biochemical pathway involves both catabolism and anabolism