Carbohydrates Flashcards
How do we store sugar in out body?
As glycogen
What are the 3 important hexoses in human biochemistry?
Glucose
Galactose
Fructose
What is a monosaccharide?
A one sugar monomer
What is disaccharide?
A two sugar polymer
Monomers in sugar are linked by what kind of bonds?
Glycosidic
How is a covalent bond formed between sugar monomers?
When the hydroxyl group of one of the monomers reacts with the anomeric carbon of another sugar monomer
What are the 3 important disaccharides in human biochemistry?
Maltose
Lactose
Sucrose
What is maltose a breakdown product of?
Starch
Why is maltose termed a reducing sugar?
As it itself is oxidised
What is lactose the main sugar in?
Milk
How is lactose formed?
Glycosidic bond between galactose and glucose
On lactose there is an anomeric carbon available for oxidation so it therefore known as what?
A reducing sugar
What is sucrose made by?
Plants
What is the sweetener sugar in most processed food?
Sucrose
What is a polysaccharide?
A polymer of sugarnmonomers ranging from medium to high molecular weight
What is a homopolysaccharide?
A sugar polymer of a single monomeric species
What is a heteropolysaccharide?
A sugar polymer that has two or more monomer species
What two polymers of glucose does starch contain?
Amylose
Amylopectin
What bonds form the backbone of starch?
The a1-a4 bonds
What bonds form the branches of starch?
The a1-a16 bonds
What bonds form the backbone of glycogen?
The a1-a4 bonds
What bonds from the branches in glycogen?
The a1-a6 bond
Which is more extensively branched glycogen or starch?
Glycogen
Where is 90% of glycogen stored in the body?
The liver and in skeletal muscle
What is glycogen rapidly broken down to yield?
Glucose
Why are the polymers of glucose osmotically inactive?
So that energy is not wasted on maintaining correct conc. gradients
What is a glycoprotein?
A protein that has carbohydrate COVALENTLY linked to it
Why do carbohydrate bind to proteins?
To increase their solubility
To influence the proteins folding and conformation
To protect the protein from degradation
To act as communication between cells (extra signalling)
What content is higher in proteoglycans: protein or carbohydrate?
Carbohydrate
How are proteoglycans formed?
Form GAGs covalently attaching to proteins
What do proteoglycans from pars of?
The connective tissues in the body
Where are proteoglycans found?
On the surface of cells or in between cells in the extracellular matrix
What is mucopolysaccharidoses caused by?
The absence of malfunction of enzymes that are required for the breakdown of glycosaminoglycans
Where in the body does carbohydrate digestion begin?
The mouth
What in the mouth breakdowns carbohydrates?
Salivary amylase
Does any carbohydrate digestion occur in the stomach?
No
What does hydrolysing mean?
Breaking down the covalent link between monomers
What are the main products of carbohydrate digestion?
Glucose, galactate and fructose
What concentration gradients drives the glucose molecules through the membrane?
Na+ gradients
How is glucose transported into epithelial cells?
Sodium flows down its concentration gradient into epithelial cells and takes glucose with it
When the sodium gradient takes glucose with it what type of transport is this?
Facilitated transport
Why after facilitated transport does Na+have to be pumped back out of the cell?
To maintain the high Na+ on the outside to keep the process going
What does the process of the absorption of glucose require?
ATP
Does the absorption of glucose continue even if blood glucose is high?
Yes - even though it is working against its concentration gradient
How is galactose absorbed?
Through a similar mode of transport as glucose - utilising gradients
How is fructose absorbed?
It binds to GLUT5 and moves down its concentration gradient
How are cellulose and hemicellulose broken down?
The polymers are broken down by gut bacteria
When gut bacteria break down cellulose an hemicellulose what do they yield?
CH4 and H2
How is absorbed glucose prevented from being re released back out of the cell?
It is converted to G-6-P which cannot diffuse back out of the cell
Why can’t G-6-P diffuse back out of the cell?
Because GLUT transporters wont recognise it
Once glucose diffuses through the intestinal epithelium cells where does it go?
Into the portal blood and on to the liver
Where is glucokinase found?
Liver
Where is hexokinase found?
In the other tissues of the body
What enzyme breaks down glucose-6-phosphate to yield free glucose?
Glucose-6-phosphatase
In skeletal muscle what is glycogen broken down into?
Lactate
From what ends is glycogen broken down- glucose is removed one monomer at a time?
Non-reducing ends
