Chapter 1 - Biological Molecules Flashcards
What are carbohydrates?
Compounds comprising only of hydrogen, carbon and oxygen units
What type of molecule is a carbohydrate?
A polymer
Characteristics of polymers
Long, complex molecules made of chains of monomers
Examples of monomers (3)
Monosaccharides, amino acids and nucleotides
What are the monomers of carbohydrates?
Monosaccharides
Examples of monosaccharides (3)
Glucose, fructose, galactose
What type of sugar is glucose and why?
Hexose sugar - it has 6 hydrogen atoms
Glucose + glucose =
Maltose
Glucose + fructose =
Sucrose
Glucose + galactose =
Lactose
What are the two types of glucose?
Alpha - and Beta - glucose
What are isomers?
Molecules with the same molecular formula but the atoms are bonded in a different way
What is a condensation reaction?
Two monosaccharides join together to form a disaccharide and a molecule of water is produced
What bond is formed in a disaccharide?
Glycosidic
What can a hydrolysis reaction do?
Break apart polymers
How does a hydrolysis reaction work?
It breaks the glycosidic bond in a disaccharide using a water molecule to form the original monosaccharides but only under the correct conditions
What are reducing sugars?
Chemicals that readily reduce others (donate electrons) when in solution
How to test for a reducing sugar?
Add 1 cm3 sugar to test tube
Add 1 cm3 benedict’s reagent
Heat in a water bath at 70c for 4 minutes
Positive result for Benedict’s test for reducing sugar?
Goes brick red if a lot of sugar is present
How to test for a non reducing sugar?
Add 1 cm3 solution to test tube
Add 1 cm3 hydrochloric acid to hydrolyse the sugar
Add sodium hydrogen carbonate until universal indicator paper turns green
Add 1cm3 benedict’s solution
Place in a water bath at 70c for 4 minutes
non-reducing result for Benedict’s test for non-reducing sugars?
Goes brick red
When are polysaccharides formed?
When more than two monosaccharides join together in a condensation reaction
Examples of polysaccharides (3)
Starch, glycogen and cellulose
Which monomers make up cellulose?
Beta glucose
Structure of cellulose
Straight, unbranched chains of beta glucose run parallel to each other
Hydrogen bonds form between the chains
This forms microfibrils, which group to make fibres
Function of cellulose
Structural support
Which monomers make up glycogen?
Alpha glucose
Structure of glycogen
Large, branched chains of alpha glucose provide a large surface area for enzymes to act upon
Function of glycogen
Stores glucose to be released when we need it
How do you test for starch?
Add a solution of iodine dissolved in potassium iodide solution and it should change from brown to blue black
Function of starch
Plants store excess glucose as starch so it can be broken down into glucose when the plant needs energy
Advantages of starch (2)
Large so can’t fit through cell membranes to upset osmotic potential
Insoluble so doesn’t impact osmotic balance
Which monomers make up starch?
Alpha glucose
Structure of starch
Made of two alpha glucose polysaccharides:
Amylose - long, unbranched chains which coil up and make it very compact
Amylopectin - long, branched chain of glucose which provides a large surface area for enzymes to act on
What are triglycerides?
One molecule of glycerol with three fatty acid tails
What are the fatty acid tails made from?
Hydrocarbons
Are fatty acid tails hydrophilic or phobic?
Hydrophobic - they repel water
How are triglycerides produced?
A condensation reaction occurs between one fatty acid tail and the glycerol molecule, forming an ester bond and a molecule of water. This happens three times
Bonding in triglycerides
Ester
How many molecules of water are released when a triglyceride is made?
3
What are the two kinds of fatty acids?
Unsaturated and saturated
Difference between saturated and unsaturated fatty acids
Unsaturated fatty acids have a double carbon bond which means that the maximum amount of hydrogen isn’t present. This also causes a characteristic kink
What are phospholipids?
One molecule of glycerol, two fatty acid tails and one phosphate tail
Is the phosphate tail hydrophilic or phobic?
Hydrophilic
How to test for lipids
Use the emulsion test:
Take a completely dry and grease fere test tube
Add 2 cm3 sample and 5cm3 ethanol
Shake to dissolve any lipids
Add 5cm3 water and shake again
If lipids are present, a white precipitate will form
Functions of phospholipids
Make up a bilayer of cell membranes
Why do phospholipids form a bilayer of cell membranes?
The heads (phosphate group) are hydrophilic and interact with the water whilst the bodies (fatty acids) are hydrophobic so the water substances can’t easily pass through
Functions of triglycerides 2
Heat insulation
Energy storage molecules
Why are triglycerides used as storage molecules?
The hydrocarbon tails contain a lot of energy which is released when they are broken down
They are insoluble so they don’t affect the osmotic balance of the cell because of their hydrophobic tails and the glycerol heads act like a barrier
What are the monomers of proteins?
Amino acids
What is a dipeptide?
When two amino acids join together
What is a polypeptide?
When more than two amino acids join together
What are proteins made from?
Multiple polypeptides
What will all amino acids contain?
An amine and a carboxyl group
What varies between amino acids?
The ‘R’ group
Formula for amine group
NH2
Formula for carboxyl group
COOH
How are polypeptides formed?
Condensation reaction of amino acids
When does the reverse reaction for making proteins happen?
Digestion
What is the bond in polypeptides?
Peptide bond
How many molecules of water are released?
1 molecule
What is the primary structure of a protein?
The sequence of multiple amino acids in a polypeptide chain
What is the secondary structure of a protein?
Hydrogen bonds form between the amino acids in the polypeptide chain, turning it into a beta pleated sheet or an alpha coil
What is the tertiary structure of a protein?
The coiled chain of amino acids coils further. More bonds form between different parts of the polypeptides
When will the tertiary structure of a protein be its final structure?
When it is made from one single polypeptide chain
What are the three bonds in the tertiary structure of a protein?
Disulfide bridges
Ionic bonds
Hydrogen bonds
When will disulfide bonds form?
Between the sulfurs in the R group of two amino acids
What is the quaternary structure of a protein?
Numerous polypeptide chains are held together by bonds
When will the quaternary structure of a protein be its final structure?
When it is made from multiple polypeptide chains
What is special about the quaternary structure of a protein?
It may include a prosthetic group ( a non-protein group)
What are the four main jobs of proteins?
Antibodies
Enzymes
Transport proteins
Structural proteins
Characteristics of enzymes
They are roughly spherical in shape because of the tight folding of the polypeptide chains
Soluble
Have roles in metabolism
Characteristics of structural proteins
Long polypeptide chains lying parallel to each other with cross-links between them
Characteristics of antibodies
Two short and two long polypeptide chains bonded together
Characteristics of transport proteins
Channel proteins found in cell membranes contain both hydrophobic and hydrophilic amino acids which cause the protein to fold up and form a channel along which substances can trave
What is the test for proteins?
Add sodium hydroxide solution to the sample to make it alkaline Add copper (II) sulfate solution Purple = protein Blue= no protein
What are enzymes?
Biological catalysts that lower the activation energy of a reaction without being affected themselves
How do enzymes lower the activation energy of a reaction? (2)
If two substrates are to be joined together, being attached to the enzyme holds them close and overcomes any repulsion
If a substrate is to be broken down then fitting it into the active site puts a strain on the bonds so it is easier to break
What is the lock and key model?
The substrate fits into the active site in the same way a key does to a lock
What is the induced fit model of enzyme action?
The active site can change to accommodate the substrate if they aren’t complimentary
Why will enzymes only catalyse one reaction?
Every enzyme has a different tertiary structure and a different shaped active site, which can be impacted by pH or temperature. This means that only one substrate is complimentary and so will be broken down
What is the effect of temperature on enzymes?
A rise in temperature increases the kinetic energy of the molecules, which leads to an increase in more successful collisions and more enzyme-substrate complexes being formed
What happens when the temperature gets too high?
The vibrating molecules break some of the bonds that hold the active site in shape, so the enzyme and substrate are no longer complimentary. The enzyme has denatured
What is the effect of pH on enzyme activity?
At any pH other than the optimum, the Oh- and H= ions mess up the hydrogen bonds in the protein’s tertiary structure. This makes the active site change shape and the enzyme is denatured.
How does enzyme concentration affect the rate of reaction?
The more enzyme molecules there are, the more likely that an enzyme-substrate complex will be formed. If the substrate concentration is limited, then it will have no further effect
How does substrate concentration affect the rate of reaction?
The higher the substrate concentration, the higher the rate of reaction because collisions will be more likely. After the ‘saturation’ point though, all the active sites are full and so an increase in substrate concentration makes no difference
What are competitive inhibitors and how do they work?
Competitive inhibitors have a similar shape to the substrate so they directly compete for the active site. When they bind, they block the active site so no enzyme-substrate complexes can be formed
Are competitive inhibitors affected by substrate concentration?
Yes, a higher concentration of substrate means that there is a lower chance of the inhibitor binding successfully to the active site. This increases the rate of reaction
What are non-competitive inhibitors and how do they work?
They bind to the allosteric site of the enzyme and cause the active site to change shape so the substrate can’t bind and create a complex
Are non-competitive inhibitors affected by substrate concentration?
No, they don’t compete directly with the substrate for the active site
What is covalent bonding?
Atoms share a pair of electrons in their outer shells
What is ionic bonding?
Ions with opposite charges attract each other - electrostatic attraction
What is hydrogen bonding?
The electrons in a bond aren’t evenly spread between the two atoms. This forms a polar molecule because one region is more electronegative than another
What is metabolism?
All the chemical reactions that take place in an organism
What is a molar solution?
A solution containing one mole of solute in each litre of solution
Why do most molecules contain carbon?
They form bonds very readily, so form a carbon ‘backbone’ for many molecules
Why does Benedict’s reagent turn red when heated with a reducing sugar?
The sugar donates electrons that turn the blue copper (II) sulfate to red copper (I) oxide
What is produced when maltose is hydrolysed?
Glucose
What is produced when starch is hydrolysed?
Maltose
