M2C3 - Biological Molecules Flashcards
Biological Molecules
What are carbohydrates made from?
Carbon, hydrogen and oxygen atoms.
Functions of carbohydrates
Energy store, energy source and structural uses.
Monosaccharides
Simplest carbohydrate. Larger carbohydrates can be made by joining them together.
Examples of monosaccharides
Glucose, Fructose, Ribose
Disaccharides
Carbohydrates made by joining two monosaccharide units. They’re bonded by glycosidic bonds.
Examples of disaccharides
Sucrose (glucose + fructose)
Maltose (glucose + glucose)
Lactose (galactose + glucose)
Polysaccharides
Carbohydrates made from a large number of monosaccharide units. They’re bonded by glycosidic bonds.
Examples of polysaccharides
Starch, cellulose, glycogen.
Structure of Glucose
C6H12O6
Alpha and Beta glucose
Alpha - the hydrogen atom is above the carbon
Beta - the hydrogen atom is below the carbon
Starch
Starch is a polysaccharide made up of many alpha glucose molecules arranged into two different structural units:
Amylopectin
Amylose
Amylose
Straight chains of alpha-glucose molecules
Joined together by a 1-4 glycosidic bond
Forms a helix shape
Amylopectin
Branched chain of alpha-glucose molecules
Joined together by 1-4 and 1-6 glycosidic bonds
Starch
Starch is the major storage molecules in plants.
Stared as grains in chloroplasts,
Produced from glucose made during photosynthesis
Broken down during respiration to provide energy.
Structure of Glycogen
Glycogen has a similar structure to amylopectin. It contains even more alpha 1-6 glycosidic bonds that produce an even more branched structure.
It is stored as small granules.
Cellulose
Consists of long chains of beta-glucose molecules joined together by beta 1-4 glycosidic bonds.
Glucose chains form rope-like microfibrils, which are layered to form a network
Water
Water is a polar molecule with the formula H2O. A hydrogen bond forms between the slightly negative oxygen and slightly positive hydrogen atoms.
Properties of water
Excellent solvent
High latent heat of evaporation
High specific heat capacity.
Functions of lipids
Energy storage, insulation and protection, hormones and water storage.
Structure of a triglyceride
Glycerol and 3 fatty acids
Main roles of triglycerides
Energy store, insoluble in water.
Structure of phospholipids
Glycerol, 2 fatty acids and a phosphate head.
Main roles of phospholipids
Cell membrane, hydrophilic and hydrophobic regions
Features of phospholipids
Hydrophilic phosphate heads, and hydrophobic fatty acid tails enable the formation of a bilayer.
Centre of the bilayer is hydrophobic so polar molecules cannot pass through it.
Fatty acid tails can be saturated or unsaturated allowing organisms to control the fluidity of the membrane.
Structure of cholesterol
Four carbon based rings
Main roles of cholesterol
Small molecule that fits into the bi-layer giving strength and stability. Buffer for fluidity
What is a protein
Long chains of amino acids (monomers) joined together with peptide bonds
Uses for proteins
Structural uses, catalytic uses, signalling uses, immunological uses and carriers.
Structure of proteins
Amine group, R-group and carboxyl group.
Primary structure of proteins
Sequence of amino acids held together by peptide bonds
Secondary structure of proteins
Coiling or folding of amino acid chains due to the hydrogen bonding in between amino acids.
Tertiary structure of proteins
Folding of the coils/pleats to form a complex 3D shape.
What bonds are present in a tertiary structure
Disulphide bonds
Ionic bonds
Hydrogen bonds
Hydrophobic and hydrophilic interactions.
Quaternary structure of proteins
Linking together of a number of polypeptide chins (e.g. haemoglobin)
What reaction joins together amino acids
Condensation reaction.
What are globular proteins?
Spherical shaped proteins caused by tightly folded polypeptide chains. Part of quaternary structure. The hydrophobic groups are on the inside and the hydrophilic groups on the outside.
Examples of globular proteins
Transport proteins - haemoglobin
Enzymes - lipase, catalase and DNA polymerase
Hormones - insulin and oestrogen
Insulin
Hormone secreted by the pancreas. Involved in regulating blood glucose levels. Quaternary structure consists of two polypeptide chains
Haemoglobin
Made up of four polypeptide chains. Each chain is wrapped around a group of atoms called a haem group, which holds an iron Fe2+ ion in the centre. Each iron ion is able to bond with two oxygen atoms (one oxygen molecule)
Catalase
Common enzyme found in nearly all living organism. Catalyses the decomposition of hydrogen peroxide to water and oxygen.
Fibrous proteins
Parallel polypeptide chains held together by cross links. They form long, rope-like fibres with high tensile strength and are generally insoluble in water
Examples of fibrous proteins
Collagen, Keratin, Elastin, Silk
Collagen
Found in connective tissues. Consists of three helical polypeptide chains which twist around each other. One in every three amino acids is a glycerine. The strands are held together by hydrogen bonds, and collagen molecules can form covalent bonds with other parallel collagen molecules to form collagen fibrils.
Keratin
Found in hair, skin and nails. Contains large proportions of cysteine, which contains sulphur so results in strong disulphide bonds forming.
Elastin
Found in skin, blood vessels and the alveoli. Allows structures to return to their original shape and size after stretching (like an elastic band)
What are the 5 different nucleotide bases
Adenine
Guanine
Thymine
Cytosine
Uracil
Purine bases
Adenine and Guanine which are double carbon rings
Pyrimidine bases
Thymine, cytosine and uracil which are single carbon rings
How are nucleotides bonded
Linked together by a condensation reaction between the phosphate of one nucleotide and the sugar of another. This is known as a phosphodiester bond
Double helix
Held together by hydrogen bonds. Each strand has a phosphate head group (5’) at one end and a hydroxyl group (3’) at the other. The two strands run antiparallel to eachother.
DNA vs RNA
DNA: Deoxyribose, AT and GC, double stranded, polynucleotide, larger
RNA: RIbose, AU and GC, single stranded, polynucleotide, smaller
Key stages of DNA replication
1) the double helix unwinds and the DNA ‘unzips’ as hydrogen bonds are broken between the polynucleotide chains.
2) complimentary base pairing occurs between free nucleotides and the exposed bases
3) as the free nucleotides are added, strong bonds form between the phosphate and the sugar groups to form the sugar phosphate backbone.
What is the role of DNA Helicase
‘unzips’ the DNA
What is the role of DNA Polymerase
Synthesises the new DNA strand by adding the nucleotides
What is the issue with DNA Polymerase
It only goes 3 to 5, it cannot go 5 to 3. This is difficult for the antiparallel strand, causing fragments Okazaki fragments
Transcription
RNA polymerase enzyme attaches to the double helix at the beginning of a gene - the hydrogen bonds between the 2 DNA strands break
Only one side of the DNA molecule is copied - this is the sense strand (template). The other uncopied side is the antisense strand (coding)
The RNA polymerase moves along the DNA adding complimentary mRNA nucleotides to the DNA bases to form a complimentary strand of mRNA
Translation
mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome.
tRNA bring amino acids to the mRNA molecule, the order determined by the base codes.
The amino acids are joined with peptide bonds to form the primary structure of the polypeptide
What is ATP?
Adenosine Triphosphate (ATP) is the universal energy carrier - it is the immediate source of energy for biological processes.
Describe the test for starch
Add a few drops of iodine to the food. If the colour changed from brown to blue/black starch is present
Describe the test for reducing sugars
Add Benedict’s solution and heat 80’C in a water bath. If red coloured precipitate forms then reducing sugars is present. The higher the concentration of colour, the higher the concentration of reducing sugars.
Describe the test for non-reducing sugars
Follow the test for reducing sugars. Then boil with HCl. Cool and neutralise with sodium hydrogen carbonate solution, then repeat the Benedict’s test. The same outcome for reducing sugars test will be present
Describe the test for a protein
Add Biuret reagent. If the colour changes from blue to lilac, proteins are present.
Describe the test for a lipid
Add ethanol and shake. White emulsion layer will form near the top if lipids are present
How do you calculate the Rf value
distance from start to substance stop / distance from origin to solvent front.
Calcium ions (Ca2+)
Involved in muscle contraction and nerve impulse transmission
Sodium ions (Na+)
Involved in co-transport, reabsorption if water in the kidney and nerves impulse transmission
Potassium ions (K+)
Involved in stomatal opening and nerve impulse transmission
Hydrogen ions (H+)
Involved in chemiosmosis, pH determination and catalysis of reactions
Ammonium ions (NH4+)
Involved in nitrogen cycle, where by bacteria convert ammonium ions into nitrate ions
Nitrate (NO3-)
Mineral ion absorbed by plants to provide a source of nitrogen to make amino acids
Hydrogencarbonate (HCO3-)
Maintains pH of blood
Chloride (Cl-)
Provide a negative charge to balance to positive sodium ion and potassium ions in cells
Phosphate (PO43-)
Involved in the formation of phospholipids for cell membranes, nuclei acid and ATP formation and making in bones
Hydroxide (OH-)
