1. Biological Molecules Flashcards
Definition: monomer
smaller units from which larger molecules are made.
Definition: polymer
molecules made from a large number of monomers joined together.
Give an example of 3 monomers in biology
monosaccharides, amino acids, nucleotides
Definition: condensation reaction
a reaction that joins two molecules together with a chemical bond involving the elimination of a water molecule
Definition: hydrolysis reaction
a reaction that breaks a chemical bind between two molecules involving the use of a water molecule
Definition: monosaccharides
the monomers from which larger carbohydrates are made
Give 3 examples of monosaccharides
glucose, galactose, fructose
Name the bond that joins two monosaccharides
glycosidic
How are disaccharides made
they are formed by the condensation of two monosaccharides
Name the disaccharide made by the condensation of glucose and glucose
maltose
Name the disaccharide made by the condensation of glucose and fructose
sucrose
Name the disaccharide made by the condensation of glucose and galactose
lactose
Give an example of 3 disaccharides
maltose, sucrose, galactose
Draw the structure of alpha glucose
.........CH2OH ...H...|\_\_\_\_\_\_\_\_\_O...H ......\/H..OH....... H..\/ ....../\ _|\_\_\_\_\_\_|_ /\ HO ...H.................OH..OH
Glycogen is formed by the condensation of which monomer
alpha glucose
Starch is formed by the condensation of which monomer
alpha glucose
Cellulose is formed by the condensation of which monomers
alpha and beta glucose
Name three reducing sugars
fructose, galactose, glucose, maltose, lactose
Describe a test for reducing sugar
- Add Benedict’s solution to the sample (sample must be in liquid form, if not grind sample up and add to water)
- Heat in water bath
Describe a positive and negative test for the reducing sugar test
Positive: turns green/yellow/orange/red
Negative: remains blue
Describe a test for non reducing sugars
- perform negative reducing sugar test.
- add more sample and add HCl
- put in water bath
- add sodium hydrogencarbonate till solution is no longer acidic
- add benedict’s solution and put in water bath
Describe a positive result for a non reducing sugar test
First test of benidicts solution will yield a negative result.
Second test after adding HCl will yield a positive test.
In the test for non reducing sugars why must you add HCl then sodium hydrogencarbonate
HCl- added to hydrolyse disaccharides to monosaccharides allowing a positive result on the second Benidicts Test.
Sodium hydrogencarbonate used to neutralise the solution as benidicts doesn’t work under acidic conditions
Describe a test for starch
- Add iodine solution to the sample
Describe a positive and negative result for the starch test
Positive: sample will turn blue/black
Negative: remains orange/brown
Name a storage molecule only found in plants
starch
Name a storage molecule only found in animals
glycogen
Describe the chains in a starch molecule
- branched and unbranched chains
- of alpha glucose
- linked by glyosidic bonds
- branched chains are coiled
What is the main role of starch in plants
Energy storage (in the form of alpha glucose)
Name 3 features of starch that make it suited for its function
- large and insoluble so it doesn’t diffuse out the cell
- compact (due to branched/ coiled nature) meaning a lot can be stored in a smaller space.
- branched chains allow the starch to be rapidly converted to glucose as many enzymes can simultaneously act on end.
Name a structural difference in starch and glycogen
glycogen has shorter chain that are more highly branched (conversely starch has longer less branched chains)
Name 3 features that make glycogen a suitable storage molecule
- large and insoluble so it doesn’t diffuse out the cell
- compact as its highly branched meaning a lot can be stored in a smaller space.
- branched chains allow the starch to be rapidly converted to glucose as many enzymes can simultaneously act on end.
Why is it important that animals use glycogen as opposed to plants using starch
glycogen is more branched so can be broken down faster by enzymes into glucose monomers. this is important as animals have a higher respiratory rate as they are more active than plants (use starch) and need glucose for respiration more rapidly
Name the elements present in lipids
C, H, O
Name the two main groups of lipids
triglycerides and phospholipids
Name 3 roles of lipids
1) source of energy (when oxidised provide 2x amount of energy than carbohydrates)
2) waterproofing (as insoluble in water, plants and insects have waxy cuticles and mammals have an oily skin secretion to preserve water)
3) insultation (fats are slow conductors of heat and electrical insulation around nerve cells)
4) protection ( fats is often stored around delicate organs)
Name the components of a triglyceride
3 fatty acids bonded to a glycerol molecule
Name the bond that joins glycerol and a fatty acid
ester bond
Describe the difference between a saturated/unsaturated fatty acid
Saturated: all the carbon bonds have the maximum number of hydrogens bonded to the carbons. (no double bonds)
Unsaturated: have at least one carbon double bond.
Name 3 features that make triglycerides a suitable storage molecule
1) they have a high energy to mass ratio making them good storage molecules as large amounts of energy can be stored in a small volume.
2) they are large and non-polar molecules so they do not affect osmosis in cells/ or the water potential of them.
3) They have a high proportion of oxygen and hydrogen so when oxidised they provide an important source of water.
Name the components of a phospholipid
a hydrophobic tail (2 fatty acids) and a hydrophilic head (a glycerol molecule and a phosphate molecule)
Describe the terms hydrophilic and hydrophobic
hydrophilic: molecules interact with water but not with fat
hydrophobic: repelled by water but mixes readily with fat
Name 2 features that make triglycerides a suitable for its function
1) the phospholipid structure allows them to form glycolipids by combining with carbohydrates on the cell surface membrane
2) due to the hydrophilic and hydrophobic parts of the phospholipid, in aqueous environments a bilayer is formed on the outside of the cell forming a hydrophobic barrier around the cell.
Describe a test for lipids
1) add ethanol
2) add water
Describe a positive and negative result for the lipid test
Positive: a milky white emulsion will appear
Negative: it will remain clear
Name the components of proteins
amino acid monomers form polypeptide chains which form proteins
Draw the structure of an amino acid
……………...R ……………….| H2N-------C-------COOH …………...….| …………..….H
How are dipeptides made
The condensation of two amino acids
Name the bond that forms between two amino acids
peptide
How many polypeptides does a functional protein contain
one or more
Name all 4 bonds present in a protein
peptide (between amino acids)
hydrogen (hold together proteins secondary and tertiary shape)
disulfide bridges (hold together proteins tertiary structure)
ionic bonds (hold together proteins tertiary structure)
Describe the primary structure of a protein
A polypeptide chain of amino acids joined by peptide bonds formed in a condensation reaction.
Why is a proteins primary structure important
- the primary structure that determines a proteins shape and therefore function
- single change in the polypeptide chain causes bonds formed in different places
- changing the proteins tertiary shape which may
- cause it to function less well or differently
- as a proteins shape is very specific to its function.
Describe the secondary structure of a protein
When amino acids are joined by peptide bonds they become polar. This allows hydrogen bonds to form (between the H d+ of -NH and O d- of C=O) between amino acids in the polypeptide chain causing it to form alpha helixes or beta plated sheets.
Describe the tertiary structure of a protein
Beta plated sheets and alpha helixes form a more specific shape which is known as the proteins tertiary structure. This is stabilized by disulfide bridges, ionic bonds and hydrogen bonds.
Describe the quaternary of a protein
complex molecules containing a number of polypeptide chains and even groups not associated with proteins such as the iron group in haemoglobin (prosthetic group). This is held together by hydrogen ionic bond + disulfide bridges
Describe a test for protein
Add biuret reagent to sample
Describe a positive and negative result for the protein test
Positive: solution turns purple
Negative: solution remains blue
Name two types of basic protein shapes and their functions
1) Fibrous proteins (eg. collagen)- structural functions
2) Globular proteins (eg. enzymes and haemoglobin)- carry out metabolic reactions
Definition: enzyme
globular proteins that act as a biological catalyst
Definition: catalyst
catalysts are substances that alter the rate of reaction without altering themselves by lowing the activation energy of the reaction
Describe the induced-fit model of enzyme action.
the induced fit model proposes the proximity of the substrate leads to a change in the enzyme that forms the functional active site so that it becomes complementary to the substrate and can bind
Name the earlier outdated enzyme action model
The lock and key model
Why was the lock and key model replaced with the induced fit model
The lock and key model suggests enzymes are rigid structures.
However, scientists have observed that other molecules could bind to enzymes at sites other than the active site,
which changed the enzymes activity.
This suggests the enzyme shape is being altered and that enzymes are a flexible structure (not as the lock and key suggests)
which caused the lock and key model to be replaced by the induced fit model
Describe and explain the effect of temperature on enzyme action
At first a rise in temperature increases rate of reaction,
as molecules have more kinetic energy.
This means more enzyme substrate complexes per unit time are formed,
as enzymes successfully collide more frequently with substrate molecules.
However, the rate begins to decrease,
as the temperature causes bonds (eg. hydrogen bonds) to break
resulting in the enzymes active site to change.
Eventually the enzyme denatures (permanently) and the reaction ceases.
Describe and explain the effect of pH on enzyme action
A change in pH (from the enzymes optimum pH) alters the charges on the amino acids
this breaks the bonds stabilizing the enzymes tertiary structure causing the active site to change shape.
This means less enzyme substrate complexes are formed per unit time resulting in a decreased rate of reaction.
Describe and explain the effect of enzyme concentration on the rate of reaction.
When there is excess substrate, an increase of enzyme concentration is proportionate to the rate of reaction.
This is because more substrate molecules are now being acted on at once.
However if there is limiting substrate increasing enzyme concentration wont effect the rate of reaction.
This is because there are enough active sites to accommodate all remaining substrate.
Describe and explain the effect of substrate concentration on the rate of reaction.
When enzyme concentration is fixed, an increase in substrate is proportionate to the rate of reaction.
This is because at low concentrations there are excess enzymes not acting on a substrate and an increase in substrate would mean more substrate is being acted on at once.
However at a certain point substrate concentration wont have an effect on reaction rate as there is a limited amount of enzyme and all the active sites are being occupied at one time.
Definition: competitive inhibitor
a molecule that binds to the active site of an enzyme
Definition: non-competitive inhibitor
a molecule that binds to an enzyme at a position other than the active site (allosteric site)
Describe and explain the effect of substrate concentration (with a fixed concentration of competitive indicator) on rate of reaction.
An increase in substrate increases the rate of reaction as competitive inhibitors reduce the rate of reaction
by occupying the enzymes active site so adding substrate would
reduce the inhibitors concentration and therefore effect.
Describe and explain the effect of substrate concentration (with a fixed concentration of non-competitive indicator) on rate of reaction.
An increase in substrate concentration does not decrease the effect of the inhibitor as they are not competing for the same active site.
However it does reduce the maximum rate of reaction as inhibitor molecules can permanently change the shape of an enzyme, reducing the number of enzymes that can catalyse the reaction.
How does cellulose differ from starch or glycogen
- beta rather then alpha glucose
- uncoiled unlike helical starch
- unbranched chains unlike starch
What is the function of cellulose
To provide support and rigidity
How is cellulose suited to its function
- made of B-glucose so long straight unbranched chians
- run parallel so form hydrogen bond cross links =support
- molecules form microfibrils which are grouped into fibres = strength
