Biological Molecules Flashcards
Monomers & Polymers
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What do the molecules of life all contain?
Carbon
Hydrogen
Oxygen
What four can they be grouped into? (molecules of life)
Carbohydrates
Lipids
Proteins
Nucleic Acids
Define monomers
Smaller units that join together to form larger molecules
Examples of monomers
Monosaccharides - galactose, glucose, fructose
Amino acids
Nucleotides
Define polymer
Molecules that form when many monomers join together
Examples of polymers
Polysaccharides
Polypeptide
Polynucleotide
Proteins
DNA/RNA
What happens in a condensation reaction?
A chemical bond (covalent bond) forms between two monomers and a molecule of water is removed
What happens in a hydrolysis reaction?
A water molecule is used to break the chemical bond (covalent bond) between the two monomers
Carbohydrates
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Name 3 hexose monosaccharides
Glucose
Fructose
Galactose
Name the bond formed when monosaccharides react
1,4 or 1,6 glycosidic bond
2 monomers = 1 chemical bond = disaccharide
Multiple monomers = many chemical bonds = polysaccharide
What are disaccharides?
Two monosaccharides joined together through a condensation reaction, forming a bond between the OH groups
Name 3 disaccharides
Maltose
Sucrose
Lactose
How are the disaccharides formed
Maltose
Sucrose
Lactose
Maltose = glucose + glucose
Sucrose = glucose + fructose
Lactose = glucose + galactose
What is a polysaccharide?
More than two monosaccharides join through a condensation reaction
When can polysaccharides form?
Can be formed from glucose monomers that are joined by 1-4 or 1-6 glycosidic bonds
Describe the structure of starch
Mixture of two polysaccharides -
Amylose - long unbranched forms coiled/ spring shape
Amylopectin - long branched chain due to 1-6 glycosidic bonds
(Alpha - glucose)
Properties of amylose and amylopectin in starch
Amylose - coiling makes it compact and can store more in smaller space
Amylopectin- branches increase surface area for enzymes to hydrolyse glycosidic bonds allowing glucose to be quickly released
Functions of starch
Plants use it as a store for excess glucose as it’s too large to leave cells and insoluble (no osmotic effect of plants)
Starch can be hydrolysed to release glucose for respiration
Describe the structure and properties of glycogen
A long, branched chain with lots of side branches - increase surface area for enzymes to hydrolyse glycosidic bonds allowing a quick release of glucose.
Compact so good for storage
Glycosidic bonds = 1-6
(Alpha glucose)
Function of glycogen
Animals - store excess glucose as glycogen in muscles and insoluble the liver - therefore an energy store.
Can be quickly released when needed for respiration
Describe the structure and properties of cellulose
Long unbranched straight chains. Cellulose chains are linked by hydrogen bonds between glucose molecules - form thicker & stronger fibres - microfibrils.
Glycosidic bonds are 1-4
(Beta glucose)
Function of cellulose
Major structural component in cell walls in plants, provides support. Allows cells to become turgid
Lipids
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What’s different about lipids? (compared to proteins & carbohydrates)
Aren’t polymers like proteins and carbohydrates
Common uses for lipids?
An energy source
To insulate organisms
Act as waterproofing
Form membranes & hormones
What are the two types of lipids?
Triglycerides
Phospholipids
Structure of triglycerides
A glycerol molecule and three fatty acid chains
How do triglycerides form?
A condensation reaction between one glycerol molecule and three fatty acid, forms an ester bond
What is a saturated fatty acid?
Contain only single bonds between carbon atoms, has all hydrogen atoms, straight chain molecules.
Higher melting point (solid @ room temp)
What is an unsaturated fatty acid?
Have double bonds between carbon atoms, fewer hydrogen atoms, double bond means it will bend or kink, can contain many carbon double bond.
Lower melting pint (liquid @ room temp)
Functions of triglycerides
Used as a energy store - a lot of energy released when the fatty acid chains are broken
Structure of phospholipids
A glycerol molecule, a phosphate group and two fatty acid chains
How do phospholipids form
An ester bond is formed by condensation reaction between the glycerol and the fatty acids
Properties of phospholipids
Phosphate group = hydrophilic and the fatty acid chains = hydrophobic Allows phospholipid to form bilayers - make up membranes in & around cell
Functions of phospholipids
Membranes, hormones
Compare phospholipids and triglycerides
- Both have glycerol backbone
- Both formed by condensation reactions
Contrast phospholipids (1) and triglycerides (2)
(1) has 2 fatty acids (2) has 3
(1) has a hydrophilic head and hydrophobic tail (2) entirely hydrophobic
(1) used for membrane formation and hormones (2) used for storage
Describe a phospholipid bilayer
Phospholipid heads = hydrophilic and their tails = hydrophobic, so when in water they form a double layer - heads outwards towards the water, tails inwards away from the water
What is the centre of a phospholipid bilayer?
Centre is hydrophobic so water soluble cannot easily pass through. Creates a barrier and allows the separation of solutions - can create different conditions either side of membrane
What’s different about proteins? (compared to lipids & carbohydrates)
Contain nitrogen as well as carbon, hydrogen & oxygen
Proteins
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What is the general structure of an amino acid?
-COOH carboxyl/ carboxylic acid group
-R variable group - only one that changes (connected to a carbon - hydrogen)
-NH2 amine/ amino group
What does the variable group contain?
Generally contains carbon (exception with glycine which is just 1 hydrogen). R group can contain other elements e.g sulfur
How many amino acids are there and how to you differentiate them?
20 amino acids present in all life forms
different combinations determine shape & structure
each has the same general structure with a variable R group (changes)
How does a dipeptide form?
When two amino acids join through a condensation reaction, peptide bond is formed, water molecule released.
peptide bond formed between amine group and hydroxyl group.
Can be broken through hydrolysis
How does a polypeptide form?
When more than two amino acids join through a condensation reaction, peptide bond is formed, water molecule released.
Can be broken through hydrolysis
Proteins can be made of either single or multiple polypeptide chains joined.
What are the four levels of protein structure?
Single chain -
Primary
Secondary
Tertiary
Multiple polypeptide -
Quaternary
Describe the primary structure
The number and sequence of amino acids in the polypeptide chain, joined together by peptide bonds.
Describe the secondary structure
Hydrogen bonds form between amino acids in the chain, causes it to coil into an α-helix or fold into a β-pleated sheet.
Many hydrogen bonds = stable
Most channel proteins = alpha helices
Describe the tertiary structure
3D shape of the polypeptide chain.
Creates a specific shape due to amino acid sequence in the chain - as hydrogen bonds, ionic bonds & disulphide bridges (covalent bonds) form between R groups.
Change to sequence of amino acids = would affect secondary and tertiary structure - as bonds would form in different places
All enzymes, antibodies & some hormones have this structure
Describe the quaternary structure
Proteins made of more than one polypeptide chain - joined to create quaternary structure
Antibodies and haemoglobin are examples of these
Other non protein groups may be associated e.g haem group in haemoglobin
Enzymes
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What do enzymes do?
They speed up the rate of metabolic reactions by lowering the activation energy of a reaction
Allow reactions to happen at a lower temperature than they would without the enzyme
They hold the substrates close together, reducing repulsion and allowing them to bond more easily or put more strain on the bonds of a substrate - break apart more easily
What are enzymes?
Proteins with a 3D structure, they have an active site that has a specific shape, only bind to a certain substrate
When an enzyme binds to a substrate an enzyme - substrate complex if formed - shape of active site is complementary to that substrate.
After reaction products leave and enzyme makes more ES-complexes
Explain the lock and key model
Original model
States the shape of an active site is exactly complimentary (like a lock) to the specific substrate molecule (the key) and the substrate fits in exactly when they collide forming and ES- complex
Explain the induced fit model
New molecular evidence suggests -
Shape of the active site of an enzyme is not exactly complimentary to the substrate molecule. When the substrate collides with the enzyme, the active site shape changes slightly to fit around the substrate and form and ES- complex
Name the 4 factors that affect the rate of enzyme action?
Enzyme concentration
Substrate concentration
Temperature
pH
How does enzyme concentration affect enzyme action?
Increasing conc - increases number of active sites available for substrate to collide with
More ES- complexes can form as enzyme conc increases
rate of reaction increase until amount of substrate becomes limiting factor - as there are more enzymes than substrate so increasing enzyme conc will no longer effect rate
Gradient can calculate how fast rate changing
How does substrate concentration affect enzyme action?
Increasing conc - increases rate of reaction as there is more substrate molecules
More ES- complexes can form as more collisions
Rate of reaction slows as enzyme conc becomes a limiting factor
When all enzyme active sites are occupied (saturation point) increasing conc will no further effect rate
How does temperature affect enzyme action?
As temp increases, rate of reaction increases - More kinetic energy - molecules move faster - more collisions, Increasing number of ES-complexes formed
Every enzyme has an optimum temp - once reached increasing temp more = decrease in rate of reaction
At high temps enzyme molecules vibrate too much - bonds break (which maintain tertiary structure) active site changes shape - no more ES-complexes can be formed - enzyme permanently denatured- reaction stops
How does pH affect enzyme action?
All enzymes have an optimum pH - most work best at pH 7 but some at pH 2 (e.g pepsin in stomach)
Above and below optimum pH for each enzyme the H+ and OH- ions disrupt ionic & hydrogen bonds holding enzymes tertiary structure in place
At extremes of pH the active site changes site and no more ES-complexes can be formed - substrate no longer fits
Enzyme permanently denatured - reaction stops
What do enzyme inhibitors do and what are the two types?
Reduce/slow the rate of reaction
Competitive & Non-competitive
Explain competitive enzyme inhibitors
Have a similar shape to the the substrate molecules
Compete with the substrate to bind to the active site of the enzyme
They block the active site so the substrate cannot bind, no ES-complexes are formed
Explain non-competitive enzyme inhibitors
Do not bind to active site as have a different shape to the substrate so don’t compete
Bind to a site away from the active site - allosteric site
Causes the active site of the enzyme to change shape so it is no longer complimentary to the substrate, no ES-complexes are formed
How does increasing the substrate concentration impact a competitive inhibitor?
Increasing conc still increases rate of reaction
Reverses the effects of a competitive inhibitor as substrate will out compete the inhibitor for active site
How does increasing the substrate concentration impact a non-competitive inhibitor?
Increasing conc will not affect rate of reaction
No effect on rate of reaction as they can’t bind to the active site
Compare competitive (1) and non-competitive (2) inhibitors
(1) similar shape to substrate - binds to active site (2) not similar - binds to allosteric site
(1) reaction can still occur when inhibitor released (2) may permanently stop reaction - active site changes shape
(1) increasing substate conc -decreases inhibitors effect (2) increasing substrate conc - has no impact on inhibitors effect
Practicals
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Test for presence of lipids
Reagent - Emulsion test - ethanol & water
1. add ethanol to sample
2. add water to the sample and shake for a minute
Positive result - Forms a milky white emulsion (layer on top of ethanol/water)
More lipids present the more milky/opaque the precipitate will be
Hazards for the presence of lipids test
Ethanol is flammable - do not conduct near a naked flame
Test for presence of proteins
Reagent - Biuret’s reagent - pale blue (dilute copper sulphate + sodium hydroxide)
1.Add excess biuret’s reagent to sample
2. Shake and leave at room temp
Positive result - purple precipitate forms
Negative result - solution stays blue
More amino acids present stronger the purple colour
chromatography can be used to identify amino acids in a mixture by separating by mass
Hazards for the presence of proteins test
Biuret’s solution is a irritant - wear goggles, wash hands on contact of skin
Test for presence of starch
Add iodine to sample
Positive result - turns blue/black
Negative result - stays brown/yellow
Test for reducing sugars (monosaccharides, some disaccharides inc maltose & lactose)
Reagent - Benedict’s reagent - pale blue
1.Add excess Benedict’s reagent to the sample
2. Heat in water bath above 80º (boiling) for 5 minutes
Positive result - predicate forms - blue to green to yellow to orange to brick red - more red = higher conc of reducing sugars
Negative result - remains blue
Hazards for the reducing sugars test
Benedict’s reagent is an irritant - wear goggles, wash hands on contact with skin
Hot water can cause burns - use caution when pouring/carrying
Test for non-reducing sugars (disaccharides, polysaccharides - sucrose)
Used if reducing test is negative
Reagent - Benedict’s reagent - pale blue
1. Add dilute Hydrochloric acid & heat in a water bath (break bonds & produce monosaccharides)
2. Cool the solution
3. Add an alkali to neutralise
4. Add excess Benedict’s reagent to the sample
Positive result - predicate forms - blue to green to yellow to orange to brick red - more red = higher conc of reducing sugars
Hazards for the non-reducing sugars test
Benedict’s reagent is an irritant - wear goggles, wash hands on contact with skin
Hot water can cause burns - use caution when pouring/carrying
Dilute HCL and NaOH can be corrosive - wear goggles and wash hands on contact with skin
