Biological molecules Flashcards
What are monomers?
Monomers are the smaller units from which larger molecules are made.
What are polymers?
Polymers are molecules made from a large number of monomers joined together.
Examples of monomers
Monosaccharides, amino acids and nucleotides
What is a condensation reaction?
A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.
What is a hydrolysis reaction?
A hydrolysis reaction breaks a chemical bond between two molecules and involves the addition of a water molecule.
What are monosaccharides?
Monosaccharides are the monomers from which larger carbohydrates are made.
Examples of monosaccharides
Glucose, galactose and fructose
What bond does a condensation reaction of two monosaccharides form?
Glycosidic bond
What does a condensation reaction of two monosaccharides form?
Disaccharide
Examples of disaccharides
Maltose, sucrose, lactose
What monosaccharides form maltose?
The condensation of two glucose molecules
What monosaccharides form sucrose?
The condensation of a glucose molecule and a fructose molecule
What monosaccharides form lactose?
The condensation of a glucose molecule and a galactose molecule.
What are the isomers of glucose?
alpha- glucose and beta-glucose
What are polysaccharides?
Long chain polymers formed by the condensation of many glucose units.
Examples of polysaccharides
Starch, glycogen, cellulose
Which polysaccharides are formed by a-glucose molecules?
Starch and glycogen
Which polysaccharides are formed by b-glucose molecules?
Cellulose
What are the two groups of lipids?
Triglycerides and phospholipids
What forms triglycerides?
Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.
What forms an ester bond?
A condensation reaction between glycerol and 3x fatty acids (RCOOH)
What is the emulsion test for lipids?
- Add ethanol and shake the test tube to dissolve any lipids in sample
- Add water and gently shake
- Milky white emulsion indicates a positive result
What are the properties of triglycerides?
Source of energy- high ratio of energy storing carbon- hydrogen bonds to carbon atoms
Energy storage- low mass to energy ratio (animals reduce mass they carry)
Insoluble- large, non polar molecules so have no osmotic effect
Source of water- high ratio of hydrogen- oxygen atoms and release water when oxidised (good for organisms in deserts)
Difference between unsaturated and saturated fatty acids
Unsaturated- one or more carbon double bonds
Saturated- no carbon double bonds
What are amino acids?
Amino acids are the monomers from which proteins are made.
What is formed by the condensation reaction of two amino acids?
A peptide bond
What is formed by the condensation reaction of many amino acids?
Polypeptide
What is the biuret test for proteins?
- Add sodium hydroxide solution
- Add drops of dilute copper (II) sulfate solution and gently mix
- Positive result turns blue to a purple colour
What is a functional protein?
containing one or more polypeptides
What is the induced fit model?
Proposal that active site forms as enzyme and substrate interact, the proximity of the substrate causes a change in enzymes functional active site (enzyme is flexible and moulds around substrate)
As it changes shape, enzyme puts a strain of substrate distorting bonds in substrate lowering activation energy.
What are the functions of DNA and RNA?
They are important information-carrying molecules. In all living cells, DNA holds genetic information and RNA transfers genetic information from DNA to the ribosomes.
What makes up a nucleotide?
A pentose, a nitrogen-containing organic base and a phosphate group.
Examples of polymers
DNA, RNA, polypeptides, polysaccharides
What are ribosomes made up of?
Ribosomes are formed from RNA and proteins.
What forms a phosphodiester bond?
A condensation reaction between two nucleotides.
Components of DNA
Deoxyribose sugar, a phosphate group and nitrogen containing organic bases adenine, cytosine, guanine or thymine.
Components of RNA
Ribose sugar, a phosphate group and nitrogen containing organic bases adenine, cytosine, guanine or uracil.
What forms ATP?
A molecule of ribose, a molecule of adenine and three phosphate groups.
Properties of water
Metabolite, solvent, relatively high heat capacity, large latent heat of vapourisation, strong cohesion
Test for reducing sugars
- Add benedicts reagent
- Heat in a water bath for 5 mins
- Positive result turns from blue to yellow/green/ brick red
What is a reducing sugar?
A sugar which can donate electrons (reduce) to another chemical.
Test for non-reducing sugars
- Add benedicts reagent
- Heat in a water bath for 5 mins
(if colour change doesnt occur a reducing sugar isnt present) - Add dilute hydrochloric acid
- Heat in a water bath for 5 mins
- Add sodium carbonate to neutralise acid
- Add benedicts reagant
- Test with pH paper to check solution is alkaline
- The place again in water bath for 5 mins
- Positive result turns yellow/green/brick red
Why is there different tests for sugars?
In order to dectect a non-reducing sugar, it must be hydrolysed into its monosaccharide components as the disaccharides do not change the colour of Benedicts reagent.
Test for starch
- Add drops of iodine solution and shake or stir
- Positive result turns from yellow to blue/ black
Starch
Polysaccharide found in parts of a plant in small grains (seeds and storage organs)
A- glucose monomers
Roles of starch
Insoluble - doesn’t have an osmotic effect
Compact and Helical- a lot can be stored in a small space
a- glucose- easily transported and readily used in respiration
Large- doesn’t diffuse out of cells
Glycogen
Polysaccharide found in animals and bacteria, major carbohydrate storage product of animals served as small granules in the muscles and liver.
A- glucose monomers
1, 4 and 1.6 glycosidic bonds
Roles of glycogen
Insoluble- has no osmotic effect
Compact- a lot can be stored in a small space
Highly branched- more ends and so hydrolysis occurs quicker, rapidly breaking glycogen down to form glucose monomers for respiration
High metabolic rate- higher respiratory rate
Cellulose
Polysaccharide found in plant cell walls providing rigidity to the cell.
B- glucose monomers
1,4 glycosidic bonds
Roles of cellulose
B - glucose monomers - form long straight unbranched chains which run parallel to each other and are cross linked by H+ bonds adding collective strength
Microfibrils- form fibres providing more strength
Permeable- allows solutes to leave or reach plasma membrane
Insoluble- no osmotic effect on cell
Roles of lipids
Source of energy, waterproofing, insulation, protection
Name for single double bond
Mono- unsaturated
Name for more than one double bond
Polyunsaturated
What makes up phospholipids
Hydrophillic head- interacts and is attracted to water, not with fat
Hydrophobic tail- repels water, mixes with fat
Structure of an amino acid
Amino group (NH2) carboxyl group (COOH)
hydrogen atom (H) variable group (R)
Formation of a peptide bond
Condensation reaction combining a OH from carboxyl group of one amino acid and with a H from amino group of another amino acid
Polypeptides structure
Primary, secondary, tertiary, quaternary
Conditions for a reaction to take place
- Collision of molecules with sufficient energy
- Free energy of products must be less than substrates
- Activation energy required
What is the activation energy?
The minimum amount of energy needed to activate the reaction
Enzyme structure
Globular protein
Active site- functional region of enzyme, made up of amino acids
What is a substrate?
Molecule which the enzyme acts on, this forms an enzyme- substrate complex where substrate is held in active site by bonds temporarily formed between amino acids
Factors affecting enzyme action
Temperature, pH, enzyme concentration, substrate concentration
Complementary base pairing in DNA
Adenine - Thymine
Guanine - Cytosine
Who worked out the structure of DNA?
James Watson and Francis Crick in 1953
- following work by Rosalind Franklin on the X- ray diffraction patterns of DNA
Stability of DNA
- Phosphodiester backbone protects organic bases in double helix
- Hydrogen bonds link organic base pairs forming bridges between phosphodiester uprights
Properties of DNA
Large molecule- carries large amount of genetic information
Helical cylinder- protects genetic information from external forces
Base pairing- allows DNA to be replicated
Hydrogen bonds- join two strands allowing them to separate during replication
Stable structure- persistent mutations are rare
Uses of ATP
Metabolic processes, movement, active transport, secretion, activation of molecules
Hydrolysis of ATP
ATP + H20 = ADP + Pi + E
- reaction catalysed by ATP hydrolase
Condensation of ADP
Conversion of ATP to ADP is a reversible reaction and so through the synthesis of ATP from ADP it is catalysed by enzyme ATP synthase. Also includes addition of phosphate molecule to ADP
Enzyme involved in hydrolysis of ATP
ATP hydrolase
Enzyme involved in synthesis of ATP
ATP synthase
Occurences of the synthesis of ATP from ADP
- Chlorophyll- containing plant cells during photosynthesis (photophosphorylation)
- Plant and animal cells during respiration (oxidative phosphorylation)
- Plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate-level phosphorylation)
Amylose
Staight chain
Unbranched and compact so broken down slowly by enzymes
1.4 glycosidic bonds
Amylopectin
Branched chain so has more accessible ends
More easily broken down by enzymes to release glucose
1,4 and 1,6 glycosidic bonds
Semi conservative replication
-unwinding of the double helix
-breakage of hydrogen bonds between complementary bases in the polynucleotide strands
-the role of DNA helicase in unwinding DNA and breaking its hydrogen bonds
- attraction of new DNA nucleotides to exposed bases on template strands and base pairing
-the role of DNA polymerase in the condensation reaction that joins adjacent nucleotides.
Role of DNA polymerase
The condensation reaction that joins adjacent nucleotides.
Role of lipids
- insulation
Fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells.
Role of lipids
- source of energy
When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water.
Role of lipids
- waterproofing
Lipids are insoluble in water and therefore useful as a waterproofing. Both plants and insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin.
Role of lipids
- protection
Delicate organs are surrounded by a layer of fat.
Structure of phospholipids
- head and tail
a hydrophilic ‘head’- interacts with water (is attracted to it) but not with fat
a hydrophobic ‘tail’- which repels from water but mixes readily with fat.
Properties of phospholipids
- Phospholipids are polar molecules so in an aqueous environment, phospholipid molecules form a bilayer within cell-surface membranes
- The hydrophilic phosphate ‘heads’ of phospholipid molecules help to hold at the surface of the cell-surface membrane.
- The phospholipid structure forms glycolipids by combining with carbohydrates within the cell-surface membrane, important in cell recognition.
Primary structure of a polypeptide
The sequence of amino acids in a polypeptide chain that are joined by peptide bonds.
Secondary structure of a polypeptide
Folding of the polypeptide chain due to hydrogen bonding into an alpha helix structure or beta pleated sheet
Tertiary structure of a polypeptide
A specific 3D shape of a protein after further folding. Maintained by different bonds, disulfide bridges, ionic bonds and hydrogen bonds.
Disulfide bridges
Fairly strong and therefore not easily broken.
Ionic bonds
Formed between any carboxyl and amino groups that are not involved in forming peptide bonds. They are weaker than disulfide bonds and are easily broken by changes in pH.
Hydrogen bonds
Numerous but easily broken. It is the 3-D shape or a protein that is important when it comes to how it functions. It makes each protein distinctive and allows it to recognise, and be recognised by, other molecules. It can then interact with them in a very specific way.
Competitive inhibitors
Have a molecular shape similar to that of the substrate. This allows them to occupy the active site of an enzyme. They therefore compete with the substrate for the available active substrate molecule sites.
Non-competitive inhibitors
Non-competitive inhibitors attach themselves to the enzyme at a binding site which is not the active site. Upon attaching to the enzyme it changes the shape of the active site in such a way that substrate molecules can no longer occupy it. and so the enzyme cannot function
Disulphide bridges
Strong covalent bonds
Function and structure of globular protein
a protein that is water-soluble and shaped like a sphere or a globe upon folding
- acting as enzymes, hormones, and transport molecules
Function and structure of fibrous protein
- can form of long chains
- insoluble in water
- useful for structure and support
What are enzymes?
Biological catalysts for intra and extra cellular reactions
Quarternary structure of a polypeptide
Two or more polypeptide chains joined together
