carbohydrates Flashcards
Function of carbohydrates
Major energy source Storage Structural Protective Cell- cell communication
Storage from of carbohydrate is
glycogen
what is a monosaccharide
Monomer of 6 C sugars (simplest form)
examples of monosaccharides
glucose, glactose and fructose
disaccharides
from monomers that are linked by glycosidic bonds
how do covalent bonds from in disaccharides
hydroxyl group of one monosaccharide reacts with anomeric carbon of another monosaccharide
What’s an anomeric carbon
carbons mirror images of each other
What does anomeric carbon do
(stabilises glucose)
allows oxidation
anomeric carbon can be either
alpha or beta
Name the 3 disaccharides
Maltose
Lactose
Sucrose
reducing sugar can
readily oxidised
Breakdown form of starch is
maltose
How is lactose formed
glycosidic bond between galactose and glucose
Lactose and Maltose are both what?
Reducing sugar
Whats sugar is only made in plants
sucrose
if anomeric carbon is available for oxidation that makes a
reducing sugar
What is an example of a nonreducing sugar
sucrose
what is a polysaccharides?
polymer of reoccurring monosaccharide monomers
A polymer with a single monomeric species is called a
Homopolysaccharides
what are heteropolysaccharides
polymers that have two or more monomer species
Examples of polysaccharides
Starch and Glycogen
What are the two types of glucose polymers in starch
amylose and amylopectin
What are glucose residues linkage in amylose
α1→4
What is the difference of amylopectin to amylose
Has additional branched linkage α1→6 (every 24-30 residues)
Does starch have lots of reducing ends?
No has a lot of nonreducing ends
what structure does amylose and amylopectin form
alpha helix
What is the linkage in glycogen
glucose (α1→4) linked sub-units
(α1→6) branches every 8 to 12 residues
Why can glycogen release glucose so rapidly
Due to many branching of nonreducing ends
Polymers in solutions are
osmotically inactive
Glucose transformed into glycogen because
can store high concentration of glucose without impacting osmocity of cells
Whats are glycoproteins
Proteins that have carbohydrates covalently attached
Carbohydrates attached to proteins do what?
Increases the proteins solubility
Influence protein folding and conformation
Protect it from degradation
Act as communication between cells
what are glycosaminoglycans composed of
Un-branched polymers made from repeating units of hexuronic acid and an amino-sugar,
what is the function of glycosaminoglycans
forms parts of extracellular mucuses and synovial fluid
Where are proteoglycans found?
found on the surface of cells or in between cells in the extracellular matrix
What do proteoglycans form part of
connective tissue
where are glycoproteins found
found on the outer plasma membrane
extra cellular matrix,
blood
and within cells in the secretory system
What is Mucopolysaccharidoses
Genetic disorder caused by the absence of enzyme that breaks down glycosaminoglycans
examples of mucopolysaccharidoses disorders
Hurler syndromes
Symptoms of Hurler syndrome
Clouding degradation of cornea, arterial wall thickens and causes inflammation and dementia
How is dementia caused due to mucopolysaccharidoses
increase in glycosaminoglycans causes a build up of Cerebrospinal fluid
First digestion of carbohydrates takes place where with what enzyme acting on substrate
Mouth as Salivary amylase hydrolyses
(α1→4) bonds of starch
Main products of carbohydrate digestion
glucose, glactose and fructose
Glucose passes through intestinal lumen and absorbed in the blood following low NA ion concentration by an
Indirect ATP powered process
What happens when blood glucose concentration is high
Glucose is still powered across the lumen into the blood
How does fructose cross lumen membrane and into the blood
Binds to the channel protein GLUT5, moving down conc gradient
What happens to polymers that can’t be digested by the gut
Increase faecal bulk
What are polymers broken down by and yield proceeded
Gut bacteria, CH4 and H2
Disaccaride deficiencies due to
generic or damage to gut wall or intestine
Characteristics of Disaccaride deficiencies
abdominal distension and cramps
Example of Disaccaride deficiencies
Lactose intolerance
absence of enzyme lactase causes what
Lactose intolerance
How is lactose broken down with disaccharide deficiency
By gut bacteria
How can lactose intolerance cause diarrhoea
as Lactose osmotically inactive, therefore draw water from the gut into the lumen
What happens when glucose enter the portal blood
immediately phosphorylated into glucose 6 phosphate
What is the purpose of G6P
traps glucose in the cell
Glucose phosphorylation enzymes
Glucokinase
Hexokinase
where is Glucokinase found
the liver
which Glucose phosphorylation enzymes catalyses high glucose concentration
Glucokinase
Hexokinase properties ie Km and Vmax
Low Km, grab glucose efficiently
Low Vmax, tissues only phosphorylate glucose at lower concentrations
What is the3 pathways of G6P
glycolysis
pentose phosphate pathway
glycogenesis
What is not present in skeletal muscle
G6P
Glycogen formed from
covalently binding
extending chains
chains then broken by glycogen-branching enzyme and re-attached via (α1→6) bonds to give branch points
Glycogen phosphorylase removes what from glycogen
G1P
Enzyme debranching enzymes help release glucose by
removing 3 glucose residues on branch and attaching to nonreducing end by alpha 1-4 bond, forming more of a straight chain
How is glucose finally removed from glycogen
Glucosidase removes the final Glc by breaking a (α1→6) linkage
what si left at the end of glycogen degradation
unbranched chain
what happens to glycogen in the liver compared to muscle
Liver, glucose 6 phosphatase produces glucose
muscle, glycolysis produces lactate giving ATP
von Gierke’s disease cause and symptoms
glucose 6-phosphatase deficiency,
low glucose level
high lactic acid level
Skeletal muscle phosphorylase deficiency causing an inability to meet glucose demand of exercise is the cause of what disease
McArdles
