L6- Carbohydrates 1 Flashcards
catabolism
breakdown of larger molecules into smaller ones
- energy released
catabolic reaction involve
oxidation-release of H atoms
H atoms become
reducing powers
anabolism
synthesises larger important cellular components from smaller molecules
- uses energy
anabolic reactions are
reductive (uses H+ released In catabolism)
sources of catabolism metabolism
amino acid (most excreted)
fatty acids
glucose
alchohol
acetyl co A
is an intermediate for all source of catabolism
Body composition predominately
lipids and proteins (even though we take in more CHO than lipids and proteins)
- we are only 1% CHO
how many stages of catabolism
4
stage 1
breakdown of molecules into molecules that can be absorbed
stage 2
glycoluysis
stage 3
Kreb/TCA cycle
stage 4
electron transport chain
formula of CHO
(CH2O)n
CHO contain which groups
aldos enad ketose groups
monosacchirdes
3-9 carbons
- glucose
- fructose
- galactose
disaccharides
2 units
- sucrose
- maltose
- galactose
oligosaccharides
(3-12 units)
- dextrin
polysacchride
10-1000 units
- glycogen
- starch
- cellulose
glucose is a
major source of sugar in the blood (5mM)
all tissue can metabolise
glucose
which cell have an absolute requirement for glucose
- RBC
- neutrophils
- innermost cells of kidney medulla
- lens of the eye
uptake of glucose depends on
[glucose]
the CNS uses … as fuel
glucose (approx 140g/24h) and no the rfules
in starvation mode the brain can evolve energy from
ketone bodies- body needs time to adapt
digestion of CHO starts in
mouth- amylase
amylase in the mouth breaks down starch nd glycogen to
dextrins
amylase does not work in
the pH of the stomach
amylase is released by the
pancreas
amylase- converts dextrin to monosaccharides
disaccharide attach to
the brush border fo the membrane of epithelial cells
cellulose is
indigestible
why is cellulose indigestible
no enzyme to breakdown the B1-4 linkage present in dietary fibre
- alpha and beta bonds are different
how are monosaccharides absorbed int he blood
Gut into epithelial cells
- Active transport (low to high conc)- energy coming from a sodium dependent glucose transport (SGLT1)
Passive transport from cells to capillaries
Passive transport (high to low conc)
- Using GLUT transporters
GLUT transporters
Glucose uptake into cells from blood in via facilitated diffusion using transport proteins (GLUT1-5)
- GLUTs can be hormonally regulated.
GLUT 1
fetal tissue, adult erythrocytes, BBB
GLUT 2
kidney, liver, pancreatic beta cells, small intestines
GLUT 3
neurones and palcenta
GLUT 4
adipose tissue, striated muscle
GLUT 4 is regulated by
insulin
GLUT 5
spermatozoa and intestine
lactose intolerance causes
Causes… Bloating, flatulence, vomiting, diarrhea etc.
types of lactose deficiency
- primary lactase deficiency
- secondary lactase deficiency
- congenital lactase deficiency
primary lactase deficiency
• Primary lactase deficiency
o Only occurs in adults
o Absence of lactase persistence allele
o High prevalence in Northwest Europe
secondary lactase deificnecy
o Damage to small intestine Gastroenteritis Coeliac disease Crohns disease UC o Occurs in both infants and adults o Generally reversible
• Congenital lactase deficiency
o Extremely rare
o Autosomal recessive defect in lactase gene
o Cannot digest breast milk
stage 2 (glycolysis)- function
o Oxidation of glucose
o Production of 2 NADH/ glucose molecule
o Synthesis of 2 ATP molecules from ADP/ glucose molecule
o Production of 2 pyruvate (C3) / 1 glucose molecule (C6)
features of glycolysis
o Central pathway of carbohydrate catabolism
o Occurs in all tissues
o Cytosolic
o Exergonic and oxidative- releases energy and hydrogen
o No loss of CO2
o With one additional enzyme (LDH), the pathway can operate anaerobically
o Irreversible pathway
key enzymes of glycolysis
Key enzymes: Hexokinase (key glucose sensor), Phosphokinase-1 and pyruvate kinase
why so many steps in glycolysis (10 enzymes, 5 coenzymes, 9 intermediates)
- Chemistry easier in small stages
- Efficient energy conservation
- Gives versatility
o Interconnection with other pathways
o Production of useful intermediates
o Allows part to be used in reverse - Can be controlled
glycolysis clinical application
- Can be used in the diagnosis of cancers
o Rate of glycolysis up to 200 times greater in cancer
o Can measure uptake of FDG
(radioactive modified hexokinase substrate)
o Imaging with positron emission tomography