Biological molecules I Flashcards
Marcomolecules:
composed of molecular subunits (monomers)
Supramolecular Complexes:
Assembly of macromolecules
Cells and organelles:
Comprised of supramolecular complexes
Biomacromolecules:
Natural polymers (MW > 5000) are assembled from monomers with MW < 500, usually
There are 4 main types of biomacromolecules,
each built using specific “building blocks”
4 types of Biomacromolecules:
Aminoacids > Proteins
Fatty acids > Phopholipids
Carbohydrates > Polysaccharides
Nucleobases > Nucleis acids (DNA/RNA)
Biomacromolecules interact with one another and self-assemble into cellular structures in very specific and highly regulated ways.
The macromolecules are then responsible for fundamental cellular functions but their interactions are often weak and reversible and reliant on their three-dimensional shape.
Biomacromolecules: Important Information
Most of their constituents (natural building blocks) are chiral molecules which exist as single enantiomers
Interactions between bio(macro)molecules are stereospecific: they require specific configurations in the interacting molecules
The environment in which bio(macro)molecules interact is mainly constituted by water: water is the solvent of all biochemical processes, and it often acts also as a reactant in biochemical reactions
Carbohydrates
Carbon (C), Hydrogen (H), Oxygen (O) atoms
Monosaccharide Molecular Formula: Cm(H2O)n
Empirical Formula (most simple sugars): C(H2O)
An exception: Deoxyribose (sugar in DNA)
Has a different molecular formula – Missing one OH group
Fischer Projections
Useful for showing molecules with multiple stereogenic centres (start at most oxidised end)
Carbohydrate
Monosaccharides (simple sugars): carbohydrates cannot be hydrolysed to more simple compounds
Disaccharides
sugar that can be hydrolysed to two monosaccharides
Polysaccharides
carbohydrates that can be hydrolysed to many monosaccharides
Monosaccharides: Classification
1) the number of carbon atoms in the carbon chain
triose (3C), tetrose (4C), pentose (5C)
2) Whether the sugar contains a ketone or an aldehyde group (aldoses or ketoses)
3) The stereochemical configuration of the asymmetric carbon atom farthest from the carbonyl group
Epimers:
diastereomers that differ only in the stereochemistry at a single carbon
Carbohydrate Chemistry:
the FGs of aldehyde to hemiacetal is important in carbohydrate chemistry:
reactions catalysed by a trace of strong acid
Hemiacetals and hemiketals - generally unstable
Nucleophilic addition to C=O
Carbohydrate Chemistry
Step 1: Protonation of the carbonyl group
Step 2: The OH group acts as a nucleophile
Step 3: Deprotonation gives a cyclic hemiacetal
Note: 5- and 6-membered cyclic hemiacetals are stable
Aldohexoses (glucose):
the equilibrium favours six-membrane rings with a hemiacetal linkage between the aldehyde carbon and the hydroxy group on C5
Aldopentoses and ketohexoses (fructose) form…
five-membered rings
OH group at C1 hemiacetal form can be up and down
Diastereomeric products = anomers
C1 = anomeric carbon
Reactions of Carbohydrates
- Reduction
- Oxidation; monosaccharides are reducing sugar, act as a reducing agent because have a free aldehyde group or a free ketone group
- Glycoside formation (conversion to an acetal)
- Alkylation to give ethers and acylation to give esters
Disaccharides
Maltose: An alffa 1-4, Glucosidic Linkage
Cellobiose: A beta 1-4C, Glucosidic Linkage
Lactose: A beta 1-4C Galactsoidic linkage
Gentiobiose: An beta 1-6C Glucodidic Linkage
Sucrose:
alpha-D-glucopyranosyl-B-D-fructofuranoside (or B-D-frutofuranosyl-a-D-glucopyranoside)
Polysaccharides (glycans):
crbohydrates contain many monosaccharide units joined
What kind of bonds are polysaccharides joined by?
glycosidic bonds
Oligosaccharides;
smaller polysaccharides, containing 3-10 monosaccharide units
all anomeric carbon atoms of polysaccharides (except for units at end of chains) are invokved in what kind of links/bonds?
acetal glycosidic links
Cellulose, glycogen, amylose, amylopectin
Cellulose
Polysaccharide of many D-glucose, monomers
Important in human nutrition
> low fibre intake is associated with constipation and some gut disease such as bowel cancer
> high fibre intake can help reduce cholesterol, reduce risk of diabetes and protect against overweight
What are the 3 main functions of Polysaccharide?
Intracellular energy storage e.g. starch, glycogen, polymers of glucose
Confer a rigid structure to cell walls e.g. cellulose
Extra/intra cellular signalling (poly or oligosaccharides attached to membranes, proteins or lipids)
Where we “See” Carbohydrates
sweeteners in drinks, aspartame
“see” lactulose; A beta 1-4 Glucosidic Linkage
an osmotic laxative
not naturally occurring sugar, manufactured synthetically
causes water to accumulate in colon - softens stool
e.g. of drug with unusual mode of action - no ‘target’
“cardiac glycosides”
Digitalis lantana - source of the CV drug digoxin
Foxgloves
Digoxin - used for HF and other CV conditions
Glucosamine
simple amino sugar
Supplement for joint health
No evidence to support any medicinal benefit
Gentamicin - carbohydrate drug (antibiotic)
phase 2 metabolism, drugs are conjugated with glucuronic acid in liver
Important mediators of cellular communication (cell-cell antibody)
e.g. AB0 Blood groups in red blood cells (RBC)
DNA and RNA
repositories of genetic information
DNA - carrier of genetic information
RNA - use of information to make all the biomolecules and components of cells
building blocks of DNA
Nucleoside = base + sugar
Nucleotide = base + sugar + phosphate
What kind of nucleotides in DNA made out of?
deoxyribonucleotides
What kind of nucleotides is RNA made out of?
ribonucleotides
DNA and RNA: Primary Structure
in polynucloetide chain, phosphodiester bonds link two consectutive nucleotide units:
rotation of phospho (deoxy)ribose backbone is
restricted: sugar can adopt four puckered conformations, with 4 atoms nearly in single plane, and 5th atom (C2 or C3) in same endo/ opposite side of plane of C5
DNA and RNA: Secondary Structure
2 chains of DNA or RNA in opposite directions, form double-stranded structures (backbone outside bases inside), held together by base-pairing, follows a specific H-bonding pattern
