Carbohydrates

Question 1

what are the three types of simple sugars found in nature?

Answer 1

glucose
galactose
fructose

Question 2

what are simple sugars made up of?

Answer 2

six carbons (hexoses)

Question 3

what are common types of disaccharides and what are they made up of?

Answer 3

sucrose - glucose + fructose
lactose - glucose + galactose
maltose - glucose + glucose

Question 4

what are the different types of polysaccharides classified?

Answer 4

branched or unbranched

homeopolysaccharides or heteropolysaccharides

Question 5

how can the branching of a polysaccharide be written as?

Answer 5

unbranched (linear) - alpha 1-4

branched - alpha 1-6

Question 6

which disaccharides can or can’t be oxidised?

Answer 6

maltose and lactose can be oxidised

sucrose can’t be oxidised

Question 7

what are the types of starch in plants and their prevalence in starch?

Answer 7

amylose (20%)

amylopectin (80%)

Question 8

what is the animal variant of starch, and where is it found?

Answer 8

glycogen

found in liver and skeletal muscle

Question 9

what is the difference between glycoproteins and proteoglycans?

Answer 9

proteoglycans - made up of GAG and protein. form part of ECM, are found in cell membranes
glycopeptides - can be involved in lots of functions, most proteins have carbohydrates attached

Question 10

what are glycosaminoglycans?

Answer 10

cells secreting mucus, made up of hexuronic acid + amino-sugar

Question 11

what are disorders caused by GAG imbalance, and what is an example?

Answer 11

mucopolysaccharidoses

eg Hurler’s syndrome

Question 12

what enzymes break down carbohydrates and where?

Answer 12

mouth - salivary amylase
duodenum - pancreatic amylase
jejunum - lactase, sucrase, maltase, isomaltase, glucoamylase

Question 13

how is glucose taken up by the blood?

Answer 13

from gut to endothelial cell (through ATPase pump)

from endothelial cell to blood (through GLUT 2 protein)

Question 14

which protein transports which carbohydrate monomer to the blood?

Answer 14

glucose and galactose - GLUT2

fructose - GLUT5 (concentration gradient)

Question 15

where is glucose stored?

Answer 15

in glycogen (liver and skeletal muscle)

Question 16

what is the first thing that happens when glucose enters liver and other tissue cells?

Answer 16

liver: glucokinase adds phosphate and traps glucose in cell

other tissues: hexokinase adds phosphate to trap glucose in cell

Question 17

what are the affinity and efficacy of glucokinase and hexokinase?

Answer 17

glucokinase - high Km and high Vmax

hexokinase - low Km and low Vmax

Question 18

how is glycogen formed?

Answer 18

glycogenin binds glucose to itself
glycogen synthase continues the job
glycogen branching enzyme adds more glucose

Question 19

how is glycogen broken down?

Answer 19

glycogen phosphorylase - removes glucose1phosphate

glucose 6 phosphatase - removes phosphate and allows glucose to leave cell

Question 20

which glycogen breakdown enzyme is only present in liver cells?

Answer 20

glucose 6 phosphatase

Question 21

what are two examples of disorders caused by lack of glucose 6 phosphatase or glycogen phosphorylase?

Answer 21

Von Gierke’s disease (no phosphatase in liver)

McArdle’s disease (phosphorylase in skel muscle)

Question 22

how many steps are there in glycolysis?

Answer 22

10

Question 23

which steps of glycolysis are spontaneous and therefore irreversible?

Answer 23

1, 3 and 10

Question 24

what characterises glycolysis in terms of oxygen need?

Answer 24

it doesn’t require any oxygen

Question 25

what is the net yield of glycolysis?

Answer 25

per cycle (G3P + DHAP): - 2ATP - 2NADH

Question 26

at which stages of glycolysis does ATP get used or produced?

Answer 26

stage 1 - ATP used (-1ATP) stage 3 - ATP used (-1ATP) stage 7 (+2ATP) stage 10 (+2ATP)

Question 27

at which stage in glycolysis is NADH formed?

Answer 27

stage 6

Question 28

what is the start and end result of glycolysis?

Answer 28

glucose --> pyruvate

Question 29

what are the three possible outcomes of pyruvate?

Answer 29

no oxygen: lactate no or low oxygen: ethanol (fermentation) oxygen: acetyl CoA (citric acid cycle)

Question 30

what catalyses the reaction from pyruvate to acetyl CoA?

Answer 30

pyruvate dehydrogenase

Question 31

what are the two main phases of glycolysis?

Answer 31

preparatory phase | pay-off phase

Question 32

what is redox balance, when and why does it occur?

Answer 32

what: it's the recycling of NAD after glycolysis when: when pyruvate becomes acetyl CoA why: so it can be used for the next glycolysis, since NAD is limited

Question 33

what are the stages of gluconeogenesis, and why do they occur?

Answer 33

Step A and B: add 4C (oxaloacetate) to lactate/pyruvate = PEP Step C: removes phosphate from fructose so it can't split (hydrolysis) Step D: remove phosphate from G6P (hydrolysis) exist to bypass the irreversible reactions from glycolysis

Question 34

what is the functional difference between NADH and NADPH?

Answer 34

NADH - used in glycolysis for glucose metabolism | NADPH - used for anabolic reactions (making nucleotides) and as antioxidant

Question 35

why does drinking alcohol stop gluconeogenesis?

Answer 35

because gluconeogenesis needs NAD to start the process, but NAD is used up to metabolise ethanol into acetate

Question 36

what is the pentose phosphate pathway?

Answer 36

a process which produces NADPH and pentose sugars, which are used for nucleotides (riboses)

Question 37

what are the two stages of pentose phosphate pathway an what do they produce?

Answer 37

oxidative (irreversible anabolic) stage - produces lot of nucleotides non-oxidative (reversible catabolic) stage - produces lots of NADPH

Question 38

what causes black water fever?

Answer 38

low NADPH levels, so oxygen free radicals don't get cleared away by antioxidant properties of NADPH - RBC burst and turn urine black

Question 39

when does gluconeogenesis occur?

Answer 39

when there is not enough glucose available for use (eg fasting or low carb diet)

Question 40

what is the yield of the citric acid cycle?

Answer 40

3x NADH 1x FADH2 1x GTP 2x CO2

Question 41

what are the main 3 intermediary molecules in the citric acid cycle, and how many carbons do they each have?

Answer 41

Acetyl CoA - 2C Oxaloacetate - 4C Citrate 6C (oxaloacetate + acetyl CoA)

Question 42

where can Acetyl CoA be produced from?

Answer 42

glycolysis or fatty acid metabolism

Question 43

what are the main functions of the citric acid cycle?

Answer 43

harvest electrons for the electron transport chain | produce CO2

Question 44

does citric acid cycle use oxygen?

Answer 44

not directly, but electron transport chain does so indirectly so does CAC

Question 45

what are the three regulatory points of the citric acid cycle?

Answer 45

pyruvate dehydrogenase isocitrate dehydrogenase alpha-ketoglutarate dehydrogenase

Question 46

what is meant by the term amphibolic in the citric acid cycle?

Answer 46

it is used for catabolic processes (glucose breakdown) and anabolic processes (intermediate molecules used as building blocks for other structures)

Question 47

what is meant by anaplerotic reaction in the citric acid cycle?

Answer 47

it's the process of replenishing intermediary molecules from the citric acid cycle when they have been used up to make other things (eg purines, pyrimidines, glutamate)

Question 48

what triggers the activation of pyruvate carboxylase in a citric acid anaplerotic reaction?

Answer 48

the build up of AcetylCoA at the start of the citric acid cycle

Question 49

what three processes are carried out by pyruvate dehydrogenase?

Answer 49

group transfer of COA-SH decarboxylation (one CO2 taken off) reduction of NAD to NADH

Question 50

how do the electrons from glycolysis-derived NADH get into mitochondrion from cytoplasm?

Answer 50

through glycerol phosphate shuttle, picked up by FAD to form FADH2

Question 51

what happens at the protein complex 1 in the electron transport chain?

Answer 51

electrons from NADH passed through Fe-S clusters to ubiquinone ubiquinone + electrons = ubiquinol, shuttle to complex 2 4 protons are pumped into the intermembranous space

Question 52

what happens at the protein complex 2 in the electron transport chain?

Answer 52

electrons from FADH2 passed through Fe=S clusters to a second ubiquinone ubiquinone + electrons = ubiquinol, shuttle to complex 3 no protons pumped out

Question 53

what happens at the protein complex 3 in the electron transport chain?

Answer 53

electrons from ubiquinol transferred onto cytochrome C cytochrome C shuttles electrons to complex 4 4 protons pumped out

Question 54

what happens at the protein complex 4 in the electron transport chain?

Answer 54

electrons pass through Fe-Cu electrons coupled with O2 to form H2O 2 protons pumped out

Question 55

what is the structure of ATP synthase?

Answer 55

F0 - sits in inner mitochondrial membrane, spins around | F1 - releases ATP

Question 56

what is the mechanism called by which ATP is formed and released, and how does it work?

Answer 56

binding-change mechanism | 3 beta subunits: one for ATP, one for ADP+Pi and one that releases ATP

Question 57

what is meant by coupling and uncoupling of the electron transport chain with ATP synthesis?

Answer 57

coupling - electron transport chain and ATP synthesis are connected uncoupling - protons are pumped out, water formed but no ATP made

Question 58

when can uncoupling of the electron transport chain and ATP synthesis happen in health and in disease, and what happens as a result?

Answer 58

heat production instead of ATP - malignant hyperthermia - brown fat in babies

Question 59

which protein complex of the electron transport chain also acts as an intermediate molecule in the citric acid cycle?

Answer 59

protein complex 2

Question 60

what is the total yield of ATP through glycolysis, citric acid cycle and electron transport chain?

Answer 60

30 to 32 ATP

Question 61

what is the mechanism that allows ATP synthase to rotate and ATP synthesis to occur?

Answer 61

proton motive force

Question 62

how are carbohydrates held together?

Answer 62

with covalent glycosidic bonds