Carbohydrates Flashcards
what are the three types of simple sugars found in nature?
glucose
galactose
fructose
what are simple sugars made up of?
six carbons (hexoses)
what are common types of disaccharides and what are they made up of?
sucrose - glucose + fructose
lactose - glucose + galactose
maltose - glucose + glucose
what are the different types of polysaccharides classified?
branched or unbranched
homeopolysaccharides or heteropolysaccharides
how can the branching of a polysaccharide be written as?
unbranched (linear) - alpha 1-4
branched - alpha 1-6
which disaccharides can or can’t be oxidised?
maltose and lactose can be oxidised
sucrose can’t be oxidised
what are the types of starch in plants and their prevalence in starch?
amylose (20%)
amylopectin (80%)
what is the animal variant of starch, and where is it found?
glycogen
found in liver and skeletal muscle
what is the difference between glycoproteins and proteoglycans?
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
what are glycosaminoglycans?
cells secreting mucus, made up of hexuronic acid + amino-sugar
what are disorders caused by GAG imbalance, and what is an example?
mucopolysaccharidoses
eg Hurler’s syndrome
what enzymes break down carbohydrates and where?
mouth - salivary amylase
duodenum - pancreatic amylase
jejunum - lactase, sucrase, maltase, isomaltase, glucoamylase
how is glucose taken up by the blood?
from gut to endothelial cell (through ATPase pump)
from endothelial cell to blood (through GLUT 2 protein)
which protein transports which carbohydrate monomer to the blood?
glucose and galactose - GLUT2
fructose - GLUT5 (concentration gradient)
where is glucose stored?
in glycogen (liver and skeletal muscle)
what is the first thing that happens when glucose enters liver and other tissue cells?
liver: glucokinase adds phosphate and traps glucose in cell
other tissues: hexokinase adds phosphate to trap glucose in cell
what are the affinity and efficacy of glucokinase and hexokinase?
glucokinase - high Km and high Vmax
hexokinase - low Km and low Vmax
how is glycogen formed?
glycogenin binds glucose to itself
glycogen synthase continues the job
glycogen branching enzyme adds more glucose
how is glycogen broken down?
glycogen phosphorylase - removes glucose1phosphate
glucose 6 phosphatase - removes phosphate and allows glucose to leave cell
which glycogen breakdown enzyme is only present in liver cells?
glucose 6 phosphatase
what are two examples of disorders caused by lack of glucose 6 phosphatase or glycogen phosphorylase?
Von Gierke’s disease (no phosphatase in liver)
McArdle’s disease (phosphorylase in skel muscle)
how many steps are there in glycolysis?
10
which steps of glycolysis are spontaneous and therefore irreversible?
1, 3 and 10
what characterises glycolysis in terms of oxygen need?
it doesn’t require any oxygen
what is the net yield of glycolysis?
per cycle (G3P + DHAP):
- 2ATP
- 2NADH
at which stages of glycolysis does ATP get used or produced?
stage 1 - ATP used (-1ATP)
stage 3 - ATP used (-1ATP)
stage 7 (+2ATP)
stage 10 (+2ATP)
at which stage in glycolysis is NADH formed?
stage 6
what is the start and end result of glycolysis?
glucose –> pyruvate
what are the three possible outcomes of pyruvate?
no oxygen: lactate
no or low oxygen: ethanol (fermentation)
oxygen: acetyl CoA (citric acid cycle)
what catalyses the reaction from pyruvate to acetyl CoA?
pyruvate dehydrogenase
what are the two main phases of glycolysis?
preparatory phase
pay-off phase
what is redox balance, when and why does it occur?
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
what are the stages of gluconeogenesis, and why do they occur?
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
what is the functional difference between NADH and NADPH?
NADH - used in glycolysis for glucose metabolism
NADPH - used for anabolic reactions (making nucleotides) and as antioxidant
why does drinking alcohol stop gluconeogenesis?
because gluconeogenesis needs NAD to start the process, but NAD is used up to metabolise ethanol into acetate
what is the pentose phosphate pathway?
a process which produces NADPH and pentose sugars, which are used for nucleotides (riboses)
what are the two stages of pentose phosphate pathway an what do they produce?
oxidative (irreversible anabolic) stage - produces lot of nucleotides
non-oxidative (reversible catabolic) stage - produces lots of NADPH
what causes black water fever?
low NADPH levels, so oxygen free radicals don’t get cleared away by antioxidant properties of NADPH - RBC burst and turn urine black
when does gluconeogenesis occur?
when there is not enough glucose available for use (eg fasting or low carb diet)
what is the yield of the citric acid cycle?
3x NADH
1x FADH2
1x GTP
2x CO2
what are the main 3 intermediary molecules in the citric acid cycle, and how many carbons do they each have?
Acetyl CoA - 2C
Oxaloacetate - 4C
Citrate 6C (oxaloacetate + acetyl CoA)
where can Acetyl CoA be produced from?
glycolysis or fatty acid metabolism
what are the main functions of the citric acid cycle?
harvest electrons for the electron transport chain
produce CO2
does citric acid cycle use oxygen?
not directly, but electron transport chain does so indirectly so does CAC
what are the three regulatory points of the citric acid cycle?
pyruvate dehydrogenase
isocitrate dehydrogenase
alpha-ketoglutarate dehydrogenase
what is meant by the term amphibolic in the citric acid cycle?
it is used for catabolic processes (glucose breakdown) and anabolic processes (intermediate molecules used as building blocks for other structures)
what is meant by anaplerotic reaction in the citric acid cycle?
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)
what triggers the activation of pyruvate carboxylase in a citric acid anaplerotic reaction?
the build up of AcetylCoA at the start of the citric acid cycle
what three processes are carried out by pyruvate dehydrogenase?
group transfer of COA-SH
decarboxylation (one CO2 taken off)
reduction of NAD to NADH
how do the electrons from glycolysis-derived NADH get into mitochondrion from cytoplasm?
through glycerol phosphate shuttle, picked up by FAD to form FADH2
what happens at the protein complex 1 in the electron transport chain?
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
what happens at the protein complex 2 in the electron transport chain?
electrons from FADH2 passed through Fe=S clusters to a second ubiquinone
ubiquinone + electrons = ubiquinol, shuttle to complex 3
no protons pumped out
what happens at the protein complex 3 in the electron transport chain?
electrons from ubiquinol transferred onto cytochrome C
cytochrome C shuttles electrons to complex 4
4 protons pumped out
what happens at the protein complex 4 in the electron transport chain?
electrons pass through Fe-Cu
electrons coupled with O2 to form H2O
2 protons pumped out
what is the structure of ATP synthase?
F0 - sits in inner mitochondrial membrane, spins around
F1 - releases ATP
what is the mechanism called by which ATP is formed and released, and how does it work?
binding-change mechanism
3 beta subunits: one for ATP, one for ADP+Pi and one that releases ATP
what is meant by coupling and uncoupling of the electron transport chain with ATP synthesis?
coupling - electron transport chain and ATP synthesis are connected
uncoupling - protons are pumped out, water formed but no ATP made
when can uncoupling of the electron transport chain and ATP synthesis happen in health and in disease, and what happens as a result?
heat production instead of ATP
- malignant hyperthermia
- brown fat in babies
which protein complex of the electron transport chain also acts as an intermediate molecule in the citric acid cycle?
protein complex 2
what is the total yield of ATP through glycolysis, citric acid cycle and electron transport chain?
30 to 32 ATP
what is the mechanism that allows ATP synthase to rotate and ATP synthesis to occur?
proton motive force
how are carbohydrates held together?
with covalent glycosidic bonds