RIN Met Lecture 2 - Energy Production:Carbohydrates 1 Flashcards
What is metabolism ?
Metabolism is the interconversion of biological molecules in small chemical steps
Catabolism -break down of larger molecules into smaller ones - can be split into four stages
What occurs in stage 1?
- Break down of fuel molecules into building block molecules for absorption
- occurs in GI tract (extra cellular)
- no energy released
- short pathways
- breakage of C-N and C-O bonds
Catabolism -break down of larger molecules into smaller ones - can be split into four stages
What occurs in stage 2?
- degradation of building block materials to a small number of organic precursors
- oxidative (H atoms released -reducing power) and some energy released
- C-C bonds broken
- occurs cytosolic and mitochondrial
- many pathways
Catabolism -break down of larger molecules into smaller ones - can be split into four stages
What occurs in stage 3?
- Krebs Cycle
- Carbon (Acetylcholine CoA) oxidised to CO2
- small fraction of energy released
- oxidative (releases reducing power )
- mitochondrial
- single pathway
Catabolism -break down of larger molecules into smaller ones - can be split into four stages
What occurs in stage 4?
Oxidative phosphorylation and electron transport
- large amount of energy is released
- ATP synthesised by conversion of reducing power
- mitochondrial
- O2 required as the last electron acceptor and reduced to H2O
- NADH and FAD2H re-oxidised
Three main dietary monosaccharides
Glucose
Fructose
Galactose
Function of glucose
Predominant sugar in human blood
Used for energy
Function of fructose
Monosaccharides
Fruit sugar
Function of sucrose
Disaccharide (Glucose and Fructose )
Table sugar
Function of lactose
Disaccharide (Galactose and Glucose )
Milk sugar
Maltose
Glucose and glucose
Disaccharide
Function of starch
Polysaccharide
Carbohydrate storage molecule in plants
Function of glycogen
Polysaccharide -highly branched
Carbohydrate storage molecule in plants
Stage 1 of catabolism -breakdown to building blocks
Explain how carbohydrates are broken down ?
Broken down by enzymes at different points
Saliva-Amylase-Starch , Glycogen -> dextrins
Pancreas -Amylase->monosaccharides
Small intestine-Lactase,sucrose,pancreatic amylase and isomaltase -Disaccharides
Why isn’t cellulose beta glucose 1-4 glycosidic bond digestives in human ?
The bond is different from alpha glucose 1-4 glycosidic bond
Amylase enzymes can’t recognise beta glycosidic linkages
What explain the biochemical basis of the clinical condition of lactose intolerance ?
Caused by low activity of lactase so a reduced ability to digest lactose
What occurs in individuals with a low level of lactase and they ingest lactose ?
It will persist into the colon where bacteria can break it down
This increase osmotic pressure of the contents and draws water into the lumen causing diarrhoea
How are monosaccharides absorbed into cells?
Use of different glucose transporters
-affinity for glucose and this transporters differ between tissues and reflect diff in the requirement of tissues for glucose
In what 2 ways can monosaccharides be absorbed into cells?
Active transport - low to high-against their conc gradient -into absorptive cells lining gut
Passive transport - high to low- down their conc gradient -absorptive cells to blood and then tissues
All use glucose transport proteins (GLUT 1-GLUT5)
Describe the glucose-dependency of some tissues
Glucose is the major sugar in the the blood and its conc is normally held relatively constant because some tissues have an absolute requirement for glucose and rate of glucose uptake into these tissue is depended on its con in the blood.
Key Function of Glycolysis
- oxidation of glucose
- NADH production (2 per glucose)
- synthesis of ATP from ADP (net gain of 2 ATP)
- produces C6 (Glycerol phosphate)and C3 (pyruvate) intermediates
Key features of Glycolysis
- central pathway of CHO catabolism
- occurs in all tissues (cytosolic)
- exergonic and oxidative
- C6 —> C3 (no loss of CO2)
- can operate anaerobically
- irreversible pathway -large negative free energy
3 main need to know enzymes of glycolysis and in what step are they used ?
Step 1-Hexokinase (Glucokinase in liver)
Step 3-Phosphofructokinase-1
Step 10-Pyruvate kinase
What is the committing step in glycolysis ?
Step 3- first step that commits glucose to metabolism vis glycolysis
