SfM- Carbohydrates Flashcards
name the two types of starch polymers
- amylose (glucose joined via a1-4 glycosidic bonds)
- amylopectin (mainly a1-4 glycosidic bonds but a1-6 every 20-30 residues = branching)
what is glycogen?
- glycogen is a strategy to store glucose in body
- polymer of glucose of a1-4 bonds but a1-6 more frequent
- makes glycogen more extensively branched than starch (more glucose can be stored in a small space)
why store glucose as glycogen?
- more compact
- has many non-reducing end, means it can be synthesised and degraded easily
- polymers form gels - making it osmotically active but doesn’t disrupt cell balance
what are glycoproteins?
- proteins that have carbohydrates covalently attached
- can vary from 1-80& carbohydrate mass
how can carbohydrates affect protein?
- increase proteins solubility
- influence protein confirmation
- increases stability
- act as communication between cells
what are glycosaminoglycans (GAGs)?
- unbranched polymers of hexuronic acid and an amino-sugar
- very slippery and sticky - also called mucopolysaccharides
- there are groups of genetic disorders meaning the enzymes that breakdown GAGs - can build up in tissues throughout the body (Hurler Syndrome)
what are proteoglycans?
- more carbohydrate than protein
- formed from GAGs attaching to proteins - when next to each other - can interlink = stronger
what are glycoproteins?
- more protein than carbohydrates
different types of carbohydrates
- starch (cereals, potatoes, rice)
- glycogen (meat)
- hemi/cellulose (plant cell walls - don’t digest it)
- oligosaccharides (peas, beans, lentils - a1-6 bonds don’t digest
- lactose/sucrose/maltose - (milk, sugar, beer)
- glucose/fructose (fruit, honey)
how are carbohydrates digested?
- mouth - amylase breaks starch into glucose
- duodenum - pancreatic amylase (same function as mouth)
- jejunum - digestion by mucosal cell-surface enzymes (isomaltases, glucoamylase, sucrase, lactase)
how is glucose absorbed?
- Na+-glucose symporter transports both Na and glucose into the cell (relies on high extracellular Na)
- glucose uniporter moves glucose out of cell into blood
how are monosaccharides absorbed?
- ATP-driven Na+ pump maintains low cellular Na+ to allow glucose to be continually pumped into cell
- galactose also uses gradients to transport
- fructose binds to the channel GLUT5 - moves down conc gradient
how is hemi/cellulose absorbed?
- these cannot be digested by the gut but increase faecal bulk, increases speed of digestion
- polymers are broken down by gut bacteria - yields CH4 and H2 = FARTS
what are the characteristics of a disaccharide deficiency?
- abdominal distension (bloat)
- cramps
- diarrhoea
what is lactose intolerance?
- lactase deficient so lactase can’t be digested
- undigested lactose is broken down by gut bacteria - causes gas build up and irritant acids
- lactose is osmotically active, thus drawing water from the gut into the lumen causing diarrhoea
what is the fate of glucose?
- Glc diffuses through intestine epithelium, into blood and into liver
- Glc is immediately phosphorylated to Glc-6-phosphate - effectively trapping it in cell
- GLUT transporters don’t recognise phosphorylated form
- catalysed by glucokinase (liver), hexokinase (any tissue)
what is the role of glycogenin?
- glycogenin begins binding glucose molecules to itself - forms chains of 8 glucose residues
what does glycogen synthase do?
- glycogen synthase takes over from glycogenin, extends the glucose chains
- chains formed by glycogen synthase are then broken down by glycogen-branching enzymes and re-attached via a1-6 bonds = branching
how is glycogen degraded?
- glycogen phosphorylase removes glucose monomers
- glucose-1-phosphate is left but not a free molecule
- transferase activity of debranching enzyme removes 3 Glc residues and attaches them via a1-4
- Glucosidase activity then removes final Glc by breaking an a1-6 linkage to release free Glc
