Glycogen and Glycolysis and energy cycles

carbohydrates are composed of?

carbon hydrogen and oxygen

2 types of carbohydrates

Monosaccharides - simple sugars that are basic units of carbohydrates eg: glucose, fructose

disaccharides - formed by linkage of two monosaccharides

eg: lactose, sucrose

in animals what is their storage form of energy

what is the structure of it?

Glycogen - highly branched polysaccharide composed of glucose

alpha 1,4 glycosidic links form main chains #

alpha 1,6 links form branches

glycogen storage sites in animals

liver - maintaining blood glucose levels

skeletal muscles - stores glycogen as energy reverse for muscle activity

also can be stored in cytoplasm as visible granules

breakdown of glycogen (glycogenolysis)

glycogen phosphorylase - enzyme that catalyses phosphorolysis of alpha 1,4 glycosidic bonds (breaks 1,4 alpha bonds) releasing glucose 1 phosphate from non reducing end of glycogen

Debranching enzyme - cuts off branches, glucanotransferase which transfers 3 glucose from the branches to main chain,

alpha 1,6 glucosidase - hydrolyses (breaks off) remaining single glucose from branch and releases the glucose

products of glycogen breakdown

glucose 1 phosphate - turned into glucose 6 phosphate

glucose 6 phosphate - can enter glycolysis

free glucose at the end - used in glycolysis or released in bloodstream

glycogen synthesis (glycogenesis)

1. Glucose activation - Glucose is converted into glucose 6 phosphate by hexokinase, then isomerised to glucose 1 phosphate by Phosphoglucomutase

2. UDP Glucose formation - Glucose 1 phosphate reacts with uridine triphosphate (UTP) to form UDP glucose (activated glucose donor)

3. Glucose synthase - enzyme transfers glucose residue from UDP glucose to non reducing end of glycogen chain to form alpha 1,4 glycosidic bond

2 key regulatory enzymes in breakdown and synthesis

glycogen phosphorylase - key enzyme in glycogen breakdown

glycogen synthase - key enzyme for glycogen synthase

hormonal effects in body

insulin - promotes glycogen synthesis in liver and muscle. When blood sugar is high

Glucagon - promotes glycogen breakdown in liver signalling low blood glucose levels

Adrenaline - promotes glycogen breakdown and prepares body for fight or flight

regulation of glucagon

in low blood sugar conditions glucagon binds to receptor leading to:

increased cyclic AMP (cAMP)

Activation of protein kinase A (PKA) which activates glycogen phosphorylase stimulating glycogen breakdown

PKA also inhibits glycogen synthesis

Regulation by Exercise

Increased calcium Ca2+ levels

release of adrenaline

Production of AMP

calcium - activates glycogen phosphorylase kinase

Adrenaline - stimulates cAMP leading to PKA activation and further phosphorylation of glycogen phosphorylase kinase

AMP - activates glycogen phosphorylase b to more active state

Fed state Regulation

when blood glucose is high:

insulin levels rise, promoting glucose uptake and synthesis

glucagon levels fall

Glucose can inhibit glycogen phosphorylase thus inhibiting glycogen breakdown

insulin signalling pathways promote activation of glycogen synthase

glycolysis process

glucose is phosphorylated

2 ATP used

Glucose is split into two - 3 carbon atoms ]

NADH is produced

ATP is produced

The molecules are converted into pyruvate

More ATP is produced

Regulation of Glycolysis - Hexokinase

Hexokinase I,II,III - High affinity for glucose, inhibited by glucose 6 phosphate

Hexokinase IV - low affinity for glucose, not inhibited by glucose 6 phosphate

Regulation of Glycolysis - Phosphofructokinase

controls main rate liming step of glycolysis

Inhibitors

ATP - high energy levels means less glucose broken down

Citrate - indicates enough energy is available

H+ - high levels indicate acidic conditions so glycolysis slows down

Activators -

AMP - signals low energy so glycolysis speeds up

Fructose 2,6 biphosphate - strongly activates PFK and increases glycolysis #

Regulation of Glycolysis - Pyruvate Kinase

controls final step of glycolysis where pyruvate is produced

Activated by:

Fructose 1,6 biphosphate speeds up final steps of glycolysis

Inhibited by: ATP - High energy means less glycolysis is needed

what happens after glycolysis

pyruvate is converted into acetyl coenzyme a and produces NADH and CO2

evidence for endosymbiotic theory for mitochondria

similar size to bacteria

possession of their own circular DNA #

Double membrane structure

Presence of their own Ribosomes and tRNAs

Roles of mitochondria

Energy production

Regulation of calcium concentrations

Detoxification of ammonia through the urea cycle

production of heat

regulation of programmed cell death (apoptosis)

structure of mitochondria

outer membrane - highly permeable membrane

Inner membrane - highly specialised and impermeable to ions, forms folds called cristae that increase surface area. This membranes has electron transport chain and ATP synthase complexes

Intermembrane space - the region between outer and inner membrane

Matrix - innermost compartment containing enzymes for pyruvate and fatty acid metabolism, as well as enzymes of citric acid cycle. Also has mitochondrial DNA, ribosomes and granules

overview of krebs cycle

takes place in mitochondrial matrix

produces co2 as a waste product

generates NADH and FADH2 that are essential for ATP synthesis

what happens in citric acid cycle / krebs cycle

• 2 molecules of CO2 are produced.

• 1 molecule of GTP(which is readily converted to ATP) is produced.

• 3 molecules of NADH are produced.

• 1 molecule of FADH2 is produced.

• A total of 8 electrons are released.

NAD AND FAD

NAD+ is an oxidising agent and accepts electrons to become reduced NADH

FAD is an oxidising agent and accepts 2electrons and 2 protons (H+) to become reduced FADH2

what is oxidative phosphorylation

process by which ATP is generated in aerobic respiration and involves electron transport chain and chemiosmosis

where is electron transport chain located and what is the process

location - inner mitochondrial membrane

process = electrons are passed from one complex to the next releasing energy at several steps. This energy is used to pump protons H+ from mitochondrial matrix into intermembrane space creating electrochemical gradient

Final electron acceptor - Oxygen accepts electrons and combines with protons to form water

what are the complexes associated with etc

complex I - accepts electrons from NADH. Pumps protons

Complex II - accepts elctrons from FADH2, but does NOT pump protons, it is not transmembrane

Complex III - Accepts electrons from ubiquinone, pumps protons

Complex IV - accepts electrons from cytochrome C and transfers them to oxygen, Pumps protons

Proton Gradient and ATP synthesis

Proton Gradient - pumping of protons by ETC creates electrochemical gradient across inner mitochondrial membrane with high concentration of H+ in intermembrane space than the matrix. This represents stored potential energy

ATP synthase - This enzyme uses energy stored in proton gradient to synthesise ATP. Protons flow back into matrix through ATP synthase allowing phosphorylation of ADP to ATP

The electrochemical gradient of protons is the driving force for ATP synthesis

catabolism vs anabolism

catabolism - the breakdown of complex molecules into simpler ones releasing energy

eg: glycolysis, oxidative phosphorylation TCA cycle

Anabolism - The synthesis of complex molecules from simpler ones and requires energy

eg: Gluconeogenesis, fatty acid synthesis

functions of pentose phosphate Pathway

produces NADPH a critical reducing power for biosynthetic reactions

Generates ribose 5 phosphate

interconverts various sugar molecules

pentose phosphate overall reaction

glucose-6-phosphate+2NADP+ + H2​O→ribose-5-phosphate+2NADPH+2H+ + CO2​

Branches of Pentose phosphate pathway

oxidative branch

converts glucose - 6 phosphate into ribulose 5 phosphate producing NADPH and CO2

Non oxidative branch - produces ribulose 5 phosphate and various sugars

where does pentose phosphate pathway occur

cytosol

how is pentose phosphate pathway utilised

high demand for ribulose 5 phosphate

equal demand for ribulose 5 phosphate and NADPH

High demand for NADPH

what is gluconeogenesis

metabolic process that synthesises glucose from non carbohydrate precursors (eg: lactate, amino acids and glycerol)

where does it take place

liver

key enzymes in gluconeogenesis

glucose 6 phosphatase

frcutose 1,6 biphosphatase

pyruvate carboxylase

phosphoenolpyruvate carboxykinase

3 main sources of glucose

lactate

amino acids

glycerol

hormone regulation of gluconeogenesis (insulin and glucagon)

insulin - promotes glycogen synthesis and glucose uptake

inhibits gluconeogenesis

Glucagon - promotes gluconeogenesis by increasing cAMP levels and stimulating enzymes

regulation of gluconeogenesis (Activation and Inhibition)

activated by: ATP, citrate, Glucagon

inhibited by; AMP, Fructose 2,6 biphosphate, Insulin

cori cycle

muscles produce lactate in anaerobic conditions

lactate goes to liver

liver converts lactate to glucose

glucose travels to the muscles