Chapter 1 - Biological Molecules Flashcards
What are the 4 carbon based compounds?
- carbohydrates
- Lipids
- Proteins
- Nucleic acids
What is the main function of Nucleic acids?
DNA - stores genetic information
RNA - transports genetic information during protein synthesis
KEY property of water 1
Metabolite
- water is a metabolite in many metabolic reactions
- Condensation reaction - monomers joined by removal of water
- Hydrolysis reaction - monomers are released by addition of a water molecule.
What do the terms metabolite and metabolism mean?
Metabolite - a substance formed in or necessary for metabolism
Metabolism - chemical processes that occur within a living organism to maintain life.
KEY property of water 2
Water as a solvent
Water is a solvent and dissolves the solute
- it is polar so makes excellent solvent of charged particles
- molecules need to move around in reactions - lots of KE for colliding
KEY property of water 3
Explain the high heat capacity of water
Water has a high heat capacity = lots of energy
- water molecules stick via hydrogen bonds so lots of energy is needed to get them to move when heating … therefore also needs to lose a lot of energy to cool down
=BUFFERING CHANGES IN TEMPERATURE
KEY property of water 4
Latent heat of vaporisation
Water has a high latent heat of vaporisation due to hydrogen bonds
SWEATING: heat energy transferred to water in body allows us to sweat without too much water loss by evaporation = good for cooling down
KEY property of water 5
What is cohesion and give an example.
Cohesion - tendency for molecules to stick together (via hydrogen bonding)
- water has large cohesive forces so can be pulled through a tube e.g. xylem vessels
Adhesion - molecules stick to walls of tubes
KEY property of water 6
What does surface tension refer to?
Explain in terms of water meeting air.
- water molecules are more stable when bonded together
- Where surface water meets air, they can’t bond with air above so they get really close to each other
… therefore allows small organisms to walk on water (pond skaters)
What are monomers and polymers?
List 3 examples for each
Monomers - molecules that can be bonded to other IDENTICAL molecules to form a larger polymer
E.g. monosaccharides, amino acids, nucleotides
Polymers - molecules made from a large number of monomers bonded together
E.g. polysaccharides, protein, nucleic acids
How are monomers joined and broken?
Joined: via a condensation reaction
- formation of a chemical bond and involves removal of a water molecule
Broken: via a hydrolysis reaction
- breaks a chemical bonds and involves use of a water molecule
What are carbohydrates made of + what is their chemical formula?
- carbohydrates are made from monosaccharides
E.g. glucose, galactose and fructose are all monosaccharides - ALL have chemical formula of C6H12O6
What is an isomer?
List the two types of glucose isomers.
- molecules that have identical chemical formulae but different structural formulae
E.g. glucose has alpha and beta glucose - both being C6H12O6
DISACCHARIDES
How are they formed and what bond is formed? List an example
- formed by the condensation of 2 monosaccharides which results in a glycosidic bond
MALTOSE is a disaccharide formed by condensation of 2 glucose molecules (broken by hydrolysis)
- chemical formulae of C12H22O11 +H2O (remember condensation = removal of water)
What are sucrose and lactose?
- SUCROSE is a disaccharide formed by the condensation of a glucose molecule and a fructose molecule
- LACTOSE is a disaccharide formed by the condensation of a glucose molecule and a galactose molecule.
How are polysaccharides formed and list the 3 main examples.
- formed by the condensation of MANY glucose units (many monosaccharides)
- STARCH + GLYCOGEN are formed by the condensation of alpha glucose
- CELLULOSE is formed by the condensation of beta glucose
- all form glycosidic bonds
List the function of starch
- major glucose (energy) store in plant cells = not found in animals
List the function of glycogen
- major glucose (energy) store in animals = not found in plants
Why are there more branches in glycogen than in starch? Is there a difference in length?
- starch is found in plants, glycogen in found in animals
- need to be more branches in glycogen as animals are more active so there are more branches for enzymes to be able to catalyse reactions on
- glycogen branches are shorter
Shape and structure of glycogen and starch
- Helical = more compact
- Insoluble in water = osmotically inactive
- Branched = glucose easily released for respiration
- Large molecule = cannot escape from cell across cell surface membrane
Where is cellulose found and what is its function?
- found in cell walls of plants
- makes cell wall strong and stops cells from bursting due to osmotic pressure (PRESSURE FROM WATER UPTAKE)
What is the shape and structure of cellulose like?
- Straight - beta glucose monomers are used in which beta glucose molecules are alternately flipped over.
- Strong - cellulose fibre made of many micro fibrils = rigidity and strength
- Side by side - weak hydrogen bonds but strong when together
What are the 4 key roles of lipids?
- Source of energy: when oxidised they provide twice as much energy as carbohydrates do at the same mass. Also release valuable water
- Waterproofing: insoluble in water so plants have waxy cuticles to conserve water
- Insulation: slows conductors of heat to retain heat
- Protection: stored around important organs
LIPID 1 - TRIGLYCERIDE
How are they formed? Refer to what bond it forms and the special type of group.
- formed by condensation of 1 molecule of glycerol and 3 molecules of fatty acid which forms an ESTER bond
- RCOOH group: COOH = carboxyl group/ carboxylic acid
- R = variable “r” group which can be saturated or unsaturated - hydrocarbon chain
LIPID 1 - TRIGLYCERIDE
Describe the different types of “r” groups in terms of saturation.
- Saturated - no double bonds between carbon atoms
- Mono unsaturated - one double bond between carbon atoms
- Poly unsaturated - more than 1 double bond between carbon atoms
- double bonds cause molecule to bend = cannot pack together = liquid at room temperature = oils
LIPID 2 - PHOSPHOLIPID
Describe how they are formed and it structure. Refer to its tail and head.
- formed by the condensation of one glycerol, 2 molecules of fatty acid and a phosphate containing group (phosphorus + oxygen)
- Hydrophilic head = attracted to water (due to phosphate group)
- Hydrophobic tail = repels water (due to fatty acids)
This creates a structure called a phospholipid bilayer = essentially cell membranes
What are proteins made of and what is the general structure?
- made by the condensation reaction of monomers called amino acids
R. = variable side chain | H2N—C—COOH | H
What is a dipeptide? Is it a polymer?
- a condensation reaction between 2 amino acids forms a peptide bond and a dipeptide
= NOT A POLYMER AS NOT MANY REPEATING UNITS
What is a polypeptide and how many polypeptides does a functional protein have?
List 2 examples of functional proteins and how many polypeptides they have.
- a polypeptide is a POLYMER formed by condensation of MANY amino acids
- a functional protein may contain 1 or more polypeptides
AMYLASE - 1 polypeptide chain
HAEMOGLOBIN - 4 polypeptide chains
LEVELS OF PROTEIN STRUCTURE 1
Primary structure
This is the sequence of amino acids in a polypeptide chain, specific to each polypeptide chain.
LEVELS OF PROTEIN STRUCTURE 2
Secondary structure
This is where there is folding of a polypeptide chain due to hydrogen bonding between N-H group of one peptide bond and C=O group of another e.g. alpha helix + beta sheets
LEVELS OF PROTEIN STRUCTURE 3
Tertiary structure
Specific 3D folding of a protein occurs due to bonding between R groups, specifically:
- Hydrogen = weakest
- Ionic = medium
- Covalent = strongest (disulfide bridge)
- hydrophobic R groups in middle, away from water
LEVELS OF PROTEIN STRUCTURE 4
What is the Quaternary structure
2 or more polypeptide chains bonded together to make final protein - not all proteins have this
E.g. haemoglobin has 4 chains
Describe the test for reducing sugars
Benedict’s test
- heat sample with Benedict’s reagent (blue)
- positive result: red or orange precipitate forms
Describe the test for non reducing sugars
Non reducing sugar = disaccharide
- do Benedict’s test and it should stay blue (negative)
- with fresh sample, boil with acid then neutralise with alkali
- heat with Benedict’s reagent again and should from red/orange precipitate
Explanation for non reducing sugars test
Step 1: proves sample is not a reducing sugar
Step 2: uses acid to HYDROLYSE disaccharide into its reducing monosaccharides ; acid then neutralised since Benedict’s test needs alkali conditions
Step 3: test for presence of these monosaccharides
Describe the test for starch
- ADD iodine in potassium iodide solution (yellow)
- Positive result should show solution turn blue/ black
Describe the test for lipids
Emulsion test
- add ethanol then add water and shake
- positive result: white milky emulsion
An emulsion is tiny insoluble droplets of one liquid forming in another
Describe the test for proteins
- add biuret reagent (blue) and it should become PURPLE/ LILAC if protein is present
What are enzymes and what sort of reactions do they catalyse?
Enzymes are biological catalysts that speed up chemical reactions in an organism.
- they catalyse a wide range of intracellular (inside cell) and extra cellular (outside cell) reactions
Can an enzyme be reused?
YES
It starts and ends in the same state so can be reused.
What determines the shape of the active site?
- enzymes are proteins
Therefore the TERTIARY structure determines shape of active site + its ability to bind to complementary substrates.
What is the activation energy and describe how enzymes change this?
- it is the energy needed to start a reaction.
Enzymes LOWER the activation energy of the reaction that it’s catalyses from around 800c to 37c for reactions to occur in the body!
Describe the induced fit model of enzyme action. [4]
- Before the reaction, the active site is not fully complementary to the substrate;
- Induced fit causes the shape of the active site to change as the substrate binds so that an enzyme-substrate complex forms;
- In turn this bends bonds in the substrate, allowing the reaction to occur with a lower activation energy;
- Bonds in the substrate are then broken so that new bonds can form;
Factors affecting enzyme activity 1
ENZYME CONCENTRATION
- increased enzyme concentration increased the rate of reaction
- This is because:
1. More active sites available, increasing the chance that substrate molecules collide with and enter active sites
2. More enzyme - substrate complexes therefore form - rate of reaction increases until SUBSTRATE CONCENTRATION becomes limiting factor, at which point the graph plateaus.
Factors affecting enzyme activity 2
SUBSTRATE CONCENTRATION
- increased substrate concentration increases the rates of reaction
This is because:
1. It increases the chance that substrate molecules collide with and enter active sites
2. More enzyme-substrate complexes form
- rate of reaction increases until ENZYME CONCENTRATION becomes limiting factor, at which point the graph levels off as all active sites are SATURATED.
Factors affecting enzyme activity 3
PH
- Low PH = increase in the concentration of H+ which attach to amino acids (R groups) of the enzyme
- This disrupts hydrogen and ionic bonds in protein= changed tertiary structure + active site shape
- enzyme becomes DENATURED so no E-S complexes can form
- Therefore rate of reaction decreases
Factors affecting enzyme activity 4
TEMPERATURE
- At higher temperature = increased KE of both enzyme and substrate
- this increases chance of collisions between enzyme and substrate = more E-S complexes = increases rate of reaction
Beyond optimal temp:
1. Polypeptide chain undergoes major vibrations which break hydrogen and ionic bonds = tertiary structure unfolds
2. Active site changes shape = denatured enzyme
3. So no more E-S complexes can form and rate of reaction decreases
What is enzyme inhibition?
Enzyme action stopped/slowed down by another substance
What are competitive inhibitors?
What do they do and are they substrates?
- competitive is where the inhibitor has a similar shape to the substrate therefore…
1. It fits in the active site of the enzyme and prevents formation of E-S complexes
2. Instead Enzyme-inhibitor complexes form - they ARE NOT SUBSTRATES - not involved in reaction, just prevent it.
What is meant by competitive inhibitors being reversible?
The inhibitors rapidly dissociates from active site then attempts to rebind
What is a non competitive inhibitor?
Where do they bind?
Has a different shape to substrate
- instead binds to the ALLOSTERIC SITE which is away from the active site
- causes tertiary structure of enzyme to change so the active site changes shape and substrates can no longer bind.
-also reversible and due to being non competitive substrate cannot out-compete inhibitor
