Biochemistry Flashcards
Carbohydrates are made of?
Carbon, hydrogen and oxygen
Main groups of carbohydrates?
Monosaccharides
Disaccharides
Polysaccharides
General formula of a monosaccharide?
(CH2O)n
Monosaccharide structure?
(CH2O)n formula
Contain carbonyl group (C=O)
Classified by number of carbons in carbon skeleton (triose, pentose)
Structure of glucose?
C6H12O6
Hexose sugar
Straight line or ring structure
In aqueous solution a cylindrical ring is formed, more stable
Difference between Alfa glucose and beta glucose?
Alfa has hydroxyl group on bottom
Beta has hydroxyl group on top
Examples of monosaccharide?
Glucose Fructose Galactose Ribose Deoxyribose
Maltose is made up of?
Two Alfa glucose molecules
Sucrose is made up of?
One alfa glucose and one beta fructose
Lactose is made up of?
One beta galactose and one Alfa glucose
How do monosaccharides form disaccharides?
Condensation reaction forming a glycosidic bond between a hydroxyl group from each molecule
Main polysaccharides?
Starch
Cellulose in plants
Glycogen in animals
Structure of starch?
Made of many Alfa glucose molecules
Either amylose and amylopectin
Amylose forms helix structure only 1,4 bonds
Amylopectin forms branch structure has 1,4 and 1,6 bonds
How to test for starch?
Use iodine
Positive is blue/black blue to iodine molecules fitting down helix structure of amylose forming a polyiodide-starch complex
Structure of glycogen?
Similar to amylopectin but more branches
1,6 bonds to form branches
Compact structure
Stored in muscles and liver cells
Structure of cellulose?
Made up of beta glucose molecules
1,4 bonds
Molecules have to rotate 180 to bond leading to long chain, hydrogen bonds form between parallel chains giving it strength
How to test for reducing sugars?
Benedicts test Reducing sugars donate an electron to copper and become oxidised to a carboxylic acid Blue= zero Green= low Orange= medium Red= high
Reducing vs non- reducing sugar?
Reducing contain an aldehyde or ketone group whereas non reducing do not
How to test for non-reducing sugars?
Heat with HCL to hydrolyse then as sodium bicarbonate to neutralise before performing benedicts test
Structure of lipids?
Contain carbon, hydrogen and oxygen
Insoluble in water, hydrophobic, non-polar, covalent bonds
Triglycerides, cholesterol, steroid, wax and phospholipids
Not true polymers
Structure of triglyceride?
Glycerol backbone joined to three fatty acid chains joined together by ester bond formed in a condensation reaction between OH group of glycerol and COOH of fatty acid
Structure of glycerol?
An alcohol
Formula of C3H8O3
Contains three hydroxyl groups
Structure of fatty acids?
Long chain hydrocarbons contain a carboxylic group (COOH) at one end
General formula is CH3(CH2)nCOOH
What is a saturated fatty acid?
Contain maximum number of hydrogen atoms so no double bonds
Straight chains
Tend to be solid at room temperature
What is an unsaturated fatty acid?
Contain some double carbon bonds as not all spaces are taken by hydrogens
Not a straight chain
Tend to be liquid at room temperature
Phospholipid structure?
Contain glycerol and two fatty acid chains
Phosphate group joined to third hydroxyl group and an alcohol group is usually bound to the phosphate group affecting the properties of the phospholipid
Why is the phospholipid head hydrophilic?
Contains a polar phosphate group
Why is the phospholipid tail hydrophobic?
Fatty acid chains repel water
Amphipathic meaning?
A molecule with both hydrophilic and hydrophobic sections
Test for lipids?
Emulsion test
Add ethanol to sample and shake to dissolve
Add to pure water after where a white cloudy emulsion forms
Lipids are non-polar so dissolve in ethanol but not water
Structure of amino acids?
Central alpha carbon An amino group (NH2) A carboxyl group (COOH) A hydrogen atom And an R group (20 different varieties which determines properties) Empirical formula of C2H4NO2+R group Tetrahedral The carbon in the middle is known as a chiral centre
Types of amino acids?
Polar
Non-polar
Electrically charged
Amino acids in relation to acid/bases?
They can act as both as the NH2 group can gain a hydrogen ion to become positively charged
The carboxyl group can lose a hydrogen ion to become negatively charged
This means they are amphoteric
What is it called when two amino acids join together?
An amide
How do amino acids bond together?
By a condensation reaction to form a peptide bond
Forms between carboxylic group on one molecule and the amino acid on the other molecule producing water OH and H bond together
Peptide bond between the carbon and nitrogen atoms
How break a dipeptide to two amino acids?
A hydrolysis reaction
Water is added
What are the four levels of protein structure?
Primary
Secondary
Tertiary
Quaternary
What is primary structure of proteins?
Sequence of amino acids in polypeptide chain, held by peptide bonds
Determined by DNA sequence
R groups alternate sides of chain so they do not get in the way of each other
What is secondary structure of proteins?
Coiling or pleating of polypeptide chain
Hydrogen bonds form between amino acid backbones (H to O)
Bonds are individually weak but collectively strong
What is tertiary structure of proteins?
Secondary structure folded into a 3D shape
Precise 3D shape due to interactions between R-groups (hydrophobic interactions, van der Waal forces, ionic bonds, hydrogen bonds, disulfide bridges)
Shape determines function
What is quaternary structure of proteins?
Multiple protein subunits held together by weak forces
Arrangement of two or more polypeptide chains held by the same bonds as tertiary structure
How to determine protein structure experimentally?
X-ray crystallography
Magnetic resonance spectroscopy
Two types of secondary structure?
Alpha helix or beta pleated sheet
What is the alpha helix?
Secondary structure
Hydrogen bonds between the NH group of one amino acid and the CO group of an amino acid four places ahead
Helix is tightly packed therefore van der Waal forces are present
R-groups point outwards from helix
What is the beta pleated sheet?
Secondary structure
Hydrogen bonds form between H and O between neighbouring polypeptide chains
Either parallel or non-parallel depending on the directions the polypeptide chains run
Anti-parallel structure is more stable as the hydrogen bonds are straight not angled
Structure of haemoglobin?
4 polypeptide chains 2 alpha subunits 2 beta subunits 4 haem groups (non-polypeptide) Haem groups contain Fe ions that binds oxygen and a histidine amino acid
What are enzymes?
Proteins
Biological catalyst that speed up reactions
What is the molecule that an enzyme acts in?
Substrate
What is the region where substrate bonds called?
Active site
Catabolic reactions of enzymes?
Larger substrates into smaller products with the release of energy (exergonic)
Chemical bonds of substrate are broken
Such as digestion, cellular respiration and detoxification
Anabolic reactions of enzymes?
Smaller substrates joined to form larger products, requires energy (endergonic)
New chemical bonds formed
Such as protein synthesis and polysaccharide synthesis
Lock and key model?
1894
Proposed substrates and active sites are complementary
Determined by tertiary structure
Induced fit model?
Active site not rigid shape but modified by reactions between R group and substrate
Increases rate of catalysis
Active shape returns to resting shape when product formed
How do enzyme speed up reactions?
Lower the activation energy needed allowing reactions to take place at lower temperatures as they are held under stress and in the correct position
What is an enzyme cofactors?
Non-protein components that are required to make the enzyme work
Can be a permanent prosthetic group or temporarily bound, for example ions, ATP, vitamins or NAD
