Metabolism - Lec 2 Flashcards
why can humans not digest cellulose ?
most sugars have alpha (a) glycosidic linkages
cellulose has beta (b) glycosidic linkages
our enzyme can break a1-4 links
but cannot break down (digest) Beta 1-4 links
so we cannot digest cellulose
Describe the biochemical basis of lactose intolerance
3 types of deficiency Primary Lactose deficiency Lack of lactase persistence allele only in adults not enough lactose produced
Secondary Lactose deficiency caused by injury to small intestine ie gastrointestineitis coeliac disease crohns disease in infants and adults is reversible
Congenital Lactose deficiency
very rare
autosomal recessive defect in lactase gene
cannot digest breast milk
symptons are - flatulance, bloating, diarrhea, vomiting
some tissues are glucose dependent, what does this mean ?
glucose is the main blood sugar
all tissues can metabolise it
some have an absolute requirement
RBC’s, Neutrophils, inner cells of kidney meddulla, lens of the eye NEED about 40g of glucose every 24 hours
the central nervous system (brain) also prefers to use glucose. 140g/24 hrs.
if given time to convert it can use ketone bodies
What are the general structure and functions of carbs
carbohydrates are of the general fromula (CH2O)n
they are ester rings with alcohol attached
an ester 1-4 bond provides polymerisations
there are monosaccherides - single sugar unit - glucose
and di/polysaccherides
- sucrose (sugar - glucose and fructose- fruit sugar)
starch (straight chain poly of glucose)
Lactose is a galactose and glucose disaccheride
glycogen is a highly branched polymer of glucose that is used for carb storage
how are carbs digested ?
hint - STAGE 1
1st of 4 stages of catabolic metabolism
complex molecules are broken down to building blocks this happens extracellulary in the GI tract - this is to convert nutrients into a form that cells can take up
the nutrients are absorbed from GI tract to circulation
No energy is produced
we do this breakdown to glucose in the GI tract in stages
Saliva - amylase - breaks starch and glycogen down
Pancreas - amylase - breaks into some monosaccherides
Small intestine - Disaccherides are broken down and all molecules are finally absorbed by- lactase sucrase Pancreatic amylase isomaltase - breaks branching bonds
How are monosaccherides absorbed ?
Hint - what are the Channels and transporters?
on the apical side of the intestinal epithelial cells there are sodium dependent glucose transporter 1 channels (2 na+ into cells with mono’s) - these bring mono’s into cell
this is ACTIVE TRANSPORT
then on the other cell side there are GLUT 2 that PASSIVELY transport glucose into the blood capilliarys
there is also a Na+ pump (3Na+ out, 2K+ in) out of cell into blood to maintain Na+ gradient - it uses ATP
blood transports glucose to target tissues
Glucose is taken up into cells via facilitated diffusion using GLUT’s 1-5 (transport proteins) -
diff GLUT diff tissues
GLUTS can be regulated by hormones like insulin in GLUT 4
Give a brief outline of STAGE 2 of Catabolism
Happens Intracellulary
many pathways - most important is GLYCOLYSIS
breakdown to metabolic intermediates (ie pyruvate)
it is oxidative - NAD is reduced to NADH
some energy as ATP is produced
What happens in Glycolsis ?
use notes to draw stages if you can
- Glucose (C6) is phosphorylated twice
- using 2 ATP -> ADP reactions
- Produces a high energy phosphate glucose (C6 intermediate)
- it is cleaved into 2x C3 molecules
- Each is reduced to produce a NAD+ -> NADH reaction (2x NADH produced)
- Retrieval of phosphate produces 2x ADP -> ATP (2x ATP produced)
- another 2x ADP -> ATP happens
- Net production of 2 ATP molcules - substrate level phosphorylation
- 2 C3 Pyruvate molecules are produced at the end !
What are the features of glycolysis
whole reaction is the oxidation of glucose
it occurs in all tissues
exothermic
irreversible reaction
can occur anaerobically with enzyme - LDH
reaciton produces some substrate level phosphorylation
what are the 3 key enzymes to remember in glycolysis?
Hexokinase - phosphorylates glucose
Phosphofructokinase - 1 - phosphorylates frucotose 6 -P to have two phosophates
a key control enzyme
Pyruvate Kinase - removes the phosphate from phosphopyruvate to produce ATP
why are the so many steps in glycolysis?
lots of enzymes and intermediates involved
chemistry is easier in small stages
Efficient for energy conversion
it gives versitility - interconnections with other pathways, produce useful intermediates and parts are revrsible (extra)
allows for some level of fine tuning and control.
give a clinical use of glycolsis
rate if glycolysis is up to 200 times greater in cancer cells
as they are rapidly dividing cells
we can measure glucose uptake in cells
we can use PET to image/visulaise cancer locations
Briefly outline STAGE 3 of catabolism
happens in mitochondria
the tricarboxylic acid cycle - TCA cycle or Krebs cycle
oxidative - release reducing power - NADH, FADH2 produced from NAD+ ect
some energy produced as GTP
many useful anabolic building blocks are made here - biosynthetic precursors
Acetyl CoA is oxidised to produce 2x CO2
Briefly outline STAGE 4 of catabolsim
happens in mitochondria
converts reducing power (NADH ect) into energy (ATP)
oxidative phosphorylation - electron transport and ATP synthesis
Carriers like NADH are re oxidised
requires O2 and prduces H20
