2 carbohydrate Flashcards
what are the 4 major functions of carbohydrates?
- Oxidation of carbohydrate is the central energy-yielding pathway
- insoluble carbo polymers serve structural and protective elements (cell walls of bacteria and plants and connective tissues in animals)
- some carbo polymers lubricate skeletal joints
- others covalently attach to proteins and lipids as a signal to determine the location + fate
What are the 3 classes of carbohydrates?
monosaccharides
oligosaccharides
polysaccharides
what are monosaccharides? what is the most abundant?
simple sugars with a single unit
d-glucose or dextrose
most of them have a sweet taste
what are oligosaccharides? what is most abundant?
short chain of monosaccharide units 2-10
disaccharides with 2 monosaccharide units (e.g. sucrose = D-glucose and D-fructose)
What are polysaccharides?
more than 20 mono units
some are linear (cellulose) some are branched (glycogen)
What are both glycogen and cellulose made up of?
both are made up of recurring units of D-glucose
are monosaccharides water soluble?
yes
what is monosaccharides molecular formula
(CH2O)n
N>=3
what are the 2 families of monosaccharides
aldoses - carbonyl group at the end of the carbon chain
ketose - carbonyl group at any other position
How can monosaccharides occur as cyclic structures?
if they have 5 or more carbon atoms in the backbone
the carbonyl group forms a covalent bond with the oxygen of a hydroxyl group along the chain
How bond forms disaccharides?
glycosidic bond - for sugars
What are most carbohydrates in nature found as?
polysaccharides
What are homopolysaccharides and heteropolysaccharides?
homo - only one type of monomer
heteropolysaccharides - 2 or more diff type of monomer
What are 5 homopolymers?
- amylose
- amylopectin
- glycogen
- cellulose
- chitin
What makes up starch
starch contains 2 types of glucose polymers
* amylose - long unbranched
* amylopectin - highly branched α1-6 linkers
all with glucose residues
what homopolysaccharides stores fuel?
starch and glycogen
What is the main storage polysaccharide of animal cells?
glycogen
Compare amylopectin to glycogen
glycogen is highly branched, but more extensively branched and more compact (also branch poitns with α1-6 linkers)
Where is glycogen most abundant and where else can it be found?
- abundant in liver (10% of liver mass)
- skeletal muscles (1-2% of muscle mass)
What homopolysaccharides have structural roles?
cellulose and chitin
what is cellulose?
- firbous tought water-insoluble
- fond in cell walls of plants
- cannt be digested by animals
- source of dietary fibre
What is chitin composed of?
- linear homopolysaccharides composed of N-acetylglucosamine residues (variants of glucose)
- the hydroxyl gorup at C2 in glucose is replaced with an acetylated amino group
Where can you find chitin?
exoskeleton of arthropods
what are glycosaminoglycans?
- heteropolysaccharide
- components of the extracellular matrix
- extracellular matrix is the extracellular space filled with a gel-like material made up of an interlocking mesh of glycosaminoglycans and fibrous proteins such as collagen, eslastin, fibronectin and laminin
What is the function of extracellular matrix?
- holds the cells together
- provides a porous pathway for diffusion of nutrients and oxygen to cells
what are glycosaminoglycans composed of?
linear polymers of repeating disaccharide units
one of the monosaccharides is either
* N-acetylglucosamine or
* N-acetylgalactosamine
The other can be
* uronic acid or
* D-glucuronic acid or
* L-iduronic acid
- some have one or more of the hydroxyls esterified with sulphate
What do glycosaminoglycans attach to form?
attached to extracellular proteins to form proteoglycans
what is an example of glycosaminoglycan?
hyaluronic acid
what is hyaluronic acid made up of?
- alternating residues of D-glucouronic acid and N-acetylglycosamine with up to 50,000 repeats
what do hyaluronic form? function?
clear and highly viscous solutions
* lubricant in the synovial fluid of joins
* giving the vitreous humour of the eye its jelly like consistency
* essential component in extracellular matrix of cartilage and tendons
what are some other glycosaminoglycans?
- chondroitin sulphate - contributes to the tensile strength of cartilages, tendons, ligaments and the walls of the aorta
- dermatan sulphate - contribute to the pliability of skil, present in blood vessels and heart valves
- keratan sulphate - no uronic acid, sulphate content variable, found in cornea, cartilage, bond, structures from dead cells: horms, hair, nails, claw, hoof
- heparan sulphate - produced by all animal cells, variable arrangments of sulphated and non-sulphated sugars
- are shorter polymers
- covalently linked to specific proteins
hot cookies dont know + sulphate
What is heparin?
intracellular form of heparan sulphate
what can you use heparin for?
- purified heparin is used as an anti-coagulant
- inhibits the coagulation of blood by binding to the protease inhibitor anti-thrombin (AT)
- the heparin-bound AT then inactivates thrombin, factor Xa and other proteases
- inactivates the blood clotting process
What are glycoconjucates?
polysaccharides covalently linked to a protein or lipid
What are 3 functions of glycoconjugates?
- provide communication between cells and external surroundings
- label protein for transport, localisation in organelles, destruction
- serve as recognition sites for extracellular signal molecules or parasites
what are the 4 types of glycoconjugates
- proteoglycans
- glycoproteins
- glycolipids
- lipopolysaccharides
what is included in a basic proteoglycan unit?
- core protein
- covalently attached glucosaminoglycan(s)
what is the point of attachment of proteoglycans?
serine residue of the sequence - Ser - Gly - X - Gly of the protein via a tetrasaccharide bridge (blue)
X means any residue
How many types of proteoglycans do mammalian cells produce?
at least 40 types
what are the function of proteoglycans?
- act as tissue organisers
- influence cellular activities such as GF activation and adhesion
- many are secreted into the extracellular matrix - provide nutrients and signaling in cells
- some are integral membrane proteins
what are the 2 major families of proteoglycans
syndecans and glypicans
syndecans
* protein has a single transmembrane domain
* extracellular domain with 3-5 chains of heparan sulphate or chondroitin sulphate
Glypicans
* protein is attached to the cell membrane via a lipid anchor
* no transmembrane domain
what are glycoproteins?
- carbohydrate-protein conjugates (similarly with proteoglycan)
- glycans (polysaccharide chains) attached are
- branched, smaller, more structurally diverse than the glycosaminoglycans of proteoglycans
How can the carbohydrate of glycoprotein attached
attached at its anomeric carbon through
* glycosidic link to the -OH group of serine (Ser) or Threonine (Thr) residue (O-link) OR
* N-glycosyl link to the amide nitrogen of an Asparagine (Asn) residue (N-linked)
How is the binding of glycoprotein and proteoglycans diferent?
Glycoproteins does not have to belong to a specific sequence, so any exposed serine can form a glycosidic link with the carbohydrate to form the the glycoprotein
proteoglycans only link to serine residue of the sequence Ser - Gly - X - Gly of the protein via a tetrasaccharide bridge
What are glycolipids?
polysaccharide chains + lipids, covalently linked via a glycosidic bond
What is an example of glycolipid?
gangliosides
* membrane lipids of eukaryotic cells
* the polar head group at the outer surface of the membrane is a complex oluigosaccharide
* some of these oligosaccharide moieties are important for the determination of blood groups in human
* the diff antigens are diff glucosaminoglycan that are exposed and linked onto the membrane lipid in RBC
What are lipopolysaccharides
- dominant feature of the outer membrane of gram-negative bacteria
- large molecules consisting of a polysaccharide chain of O-specific chain and core linked to the lipid via covalent bond
- prime targets of antibodies produces by the immune system in response to a bacterial infection
