Carbs 1 Flashcards
What is the general formula for carbs
(CH2O) n
What is a carb with a ketone group called
ketose
What is a carb with an aldehyde group called
aldoes
Describe the structure of a monosaccharide
have an asymmetrical carbon
exist as either D or L forms
natural forms are D
How are disaccharides made
condensation reaction between two monosaccharides to form a glycosidic bond
how many units is an oligosaccharide
3-12
give examples of polysaccharides
glycogen
cellulose
starch
What are two important features of sugars
hydrophilic
partially oxidised (require less oxygen)
What are the 4 stages of metabolism
1) extracellular breakdown
2) glycolysis/ pentose phosphate
3) TCA cycle
4) ETC and ox phosphorylation
List all the dietary carbs
- glucose
- fructose
- sucrose
- lactose
- maltose
- starch
Name the enzymes involved in extracellular breakdown
glycosidase enzymes
- salivary amylase
- pancreatic amylase
Where are the glycosidase enzymes found
large glycoproteins that are attached to the brush border membranes of epithelial cells lining small intestine
Where do the pancreatic amylase enzymes work
duodenum
what enzymes breakdown diasaccharides
diasaccharidases
- lactase
- sucrase
- isomaltase
- glycomaltase
After stage 1 how and where are sugars transported
- actively transported to cells lining gut
- facilitated diffusion to blood then tissues by glucose transport proteins (GLUT1 - GLUT5)
Which GLUT transports glucose to skeletal muscle and adipose tissue
GLUT 4
Which cells are dependent only on glucose
RBC
neutrophils
CNS prefers
kidney medulla
lens of eye
Where does glycolysis occur
cytoplasm
Why is glycolysis important
- oxidation of glucose to pyruvate
-NADH production - ATP synthesis
- important intermediates
How many enzyme catalysed steps are there in glycolysis
10
Why is phase 1 of glycolysis known as investment phase
uses 2 ATP molecules
What is the enzyme of reaction 1 in glycolysis
hexokinase
glucokinase in liver
What happens in reaction one of glycolysis
glucose is phosphorylated to glucose-6-phosphate
Why does reaction one of glycolysis require ATP
to phosphorylate glucose
Why is reaction 1 of glycolysis important
it phosphorylates glucose so
- makes it neg charge so cannot leave cell
- increases reactivity
- allows for substrate level phosporylation
What is the enzyme for reaction 3 in glycolysis
phosphofructokinase-1
What is the main regulatory enzyme in glycolysis
phosphofructokinase-1
What happens in reaction 2 of glycolysis
glucose-6-phosphate is isomerised to fructose-6-phosphate
What happens in reaction 3 of glycolysis
fructose-6-phosphate is phosphorylated to fructose-1,6-bisphosphate
What are some important features of reactions 1 and 3 of glycolysis
- large neg delta G
- irreversible
why is phase 2 of glycolysis known as payback
4 ATP molecules are made to replace the two used and generate two new
What is the enzyme for reaction 10 of glycolysis
pyruvate kinase
In which reactions of glycolysis does substrate phosphorylation occur
7 & 10
What reaction is NADH produced
6
Why must a constant supply of NAD be available for glycolysis
to make NADH in reaction 6
Why must the NADH be reoxidised to NAD
to be used again to make NADH
When does NADH get reoxidised
in stage 4 in cells with a mitochondria ETC
however in cells without mitochondria or lack of O2 NADH is converted back to NAD by lactate dehydrogenase in anaerobic glycolysis
What enzyme converts NADH to NAD in cells without mitochondria or anaerobic resp
lactate dehyrogenase
What are the important intermediates in glycolysis
- 1,3- bisphosphoglycerate
- DHAP (dihydroxyaetone-p)
What is the importance of the intermediate 1,3- bisphosphoglycerate
is converted to 2,3- bisphosphoglycerate by the enzyme bisphosphoglycerate mutase
produced in RBC regulates affinity of Hb to oxygen
What is the importance of DHAP intermediate
- converted to glycerol phosphate by enzyme glycerol-3-phosphate dehydrogenase
- this is important for triaclyglyceride and phospholipid synth
- produced in adipose and liver
Why can humans not digest cellulose
humans do not have the enzymes to break β-1,4 linkages in cellulose
What are symptoms of lactose intolerance
bloating (colonic bacteria releases gas)
diahorrea (lactose in colon means higher oncotic pressure so more water drawn out)
flatulence
vomiting
What happens to lactase activity after infancy in most populations
declines
what is the phenotype name for lactase enzyme remaining after infancy
lactase persistance phenotype
What is the primary deficiency of lactose intolerance and who does it affect
absence of lactase persistant allele
high prevalence in NW euope
adults only
What is a secondary deficiency of lactose intolerance cause by and who does it affect
caused by injury to small intestine
(coeliac, Crohns, ulcerative colitis, gastroenteritis)
infants and adults
generally reversible
What is a congenital deficiency to lactose caused by
rare defect in lactase gene
cannot digest breast milk
What is the treatment for lactose intolerance
remove all lactose from diet
