Topic 1 : Biological molecules Flashcards
1
Q
Monomers
A
Smaller, repeating units from which larger molecules are made
2
Q
Polymers
A
Molecules made from many monomers
3
Q
Condensation reaction
A
Formation of a chemical bond between 2 molecules, joining them together and releasing a water molecule
4
Q
Hydrolysis reaction
A
Breaking a chemical bond between 2 molecules, separating them using a water molecule
5
Q
Monosaccharides
A
Monomers from which larger carbohydrates are made, e.g. glucose, fructose and galactose
6
Q
Function of starch
A
Energy storage in plant cells
7
Q
Function of glycogen
A
Energy storage in animal cells
8
Q
Function of cellulose
A
Provides strength and structural support to plant cell walls
9
Q
Structure of starch
A
- Polysaccharide of alpha glucose
- Contains amylose which has 1,4 - glycosidic bonds so unbranched
- Contains amylopectin which has 1,6 and 1,4 - glycosidic bonds so it is branched.
10
Q
Structure of glycogen
A
- Polysaccharide of alpha glucose
- Contains 1,4 and 1,6 - glycosidic bonds so it is highly branched
11
Q
Structure of cellulose
A
- Polysaccharide of beta glucose
- Contains 1,4 - glycosidic bonds and each beta glucose is inverted 180 degrees so it forms long, straight and unbranched chains.
- Parallel chains are linked by hydrogen bonds to form microfibrils
12
Q
How does the structure of starch relate to its function
A
- Insoluble so it doesn’t affect water potential of the cell
- Large and insoluble so it can’t leave the cell across the cell membrane
- [AMYLOSE] Helical structure so it’s compact, a lot can be stored in a small area
- [AMYLOPECTIN] Branched so more compact, a lot can be stored in a small area.
- [AMYLOPECTIN] Branched so it has more ends for hydrolysis so glucose is released more readily for respiration
13
Q
How does the structure of glycogen relate to its function
A
- Insoluble so it doesn’t affect water potential of the cell
- Large and insoluble so it can’t leave the cell across the cell membrane
- Branched so more compact, a lot can be stored in a small area.
- Branched so it has more ends for hydrolysis so glucose is released more readily for respiration
14
Q
How does the structure of cellulose relate to its function
A
Every other beta glucose molecule is inverted which forms long, straight, unbranched chains.
Hydrogen bonds form between parallel strands (crosslinks) to form microfibrils
Due to collective strength of hydrogen bonds, strength is provided to plant cell walls.
15
Q
Test for reducing sugars [monosaccharides, maltose, lactose]
A
- Add Benedict’s solution to the sample
- Heat in a boiling water bath
- If reducing sugar is present, solution goes from blue to a brick red precipitate.
16
Q
Test for nonreducing sugars [sucrose]
A
- Do Benedict’s test for reducing sugars and the solution stays blue - negative result
- To a new sample add dilute hydrochloric acid and heat in a boiling water bath - to hydrolyse into monosaccharides
- Add sodium hydrogencarbonate to neutralise the solution
- Add Benedict’s solution and heat in a boiling water bath
- If nonreducing sugar is present a brick red precipitate forms.
17
Q
Test for starch
A
- Add iodine dissolved in potassium iodide and shake
- The solution goes from orange-brown to blue-black if starch is present.
18
Q
Saturated fatty acids
A
Contain no C=C double bond
19
Q
Unsaturated fatty acids
A
Contain one or more C=C double bond
20
Q
Formation of triglycerides
A
Condensation reactions between glycerol and 3 fatty acids forming 3 ester bonds [ ester bond between glycerol and fatty acid] , releasing 3 water molecules.
21
Q
Function of triglycerides
A
Energy storage
22
Q
How does the structure of triglycerides relate to its function
A
- High ratio of C-H bonds to carbon atoms in hydrocarbon chain so used in respiration to release more energy than the same mass of carbohydrates
- Hydrophobic so insoluble in water so no effect on the water potential of the cell
23
Q
Function of phospholipids
A
Make up the bilayer in a cell membrane [allowing diffusion of lipid-soluble or very small substances and restricting movement of water soluble or larger substances]
24
Q
How does the structure of phospholipids relate to its function
A
- Formed of hydrophilic phosphate heads and hydrophobic fatty acid tails
- Phosphate heads are attracted to water so point to the aqueous environment (water) on either side of the membrane
- Fatty acid tails are repelled by water so point away from the aqueous environment / to interior of the membrane
25
Emulsion test for lipids
- Add ethanol to the sample and shake
- Then add water
- If lipids are present in the sample, a milky white emulsion forms
26
Formation of a peptide bond
Condensation reaction between carboxyl (COOH) group of one amino acid and the amine (NH2) group of another amino acid, removing a water molecule and forming a peptide bond
27
Primary structure of a protein
The sequence of amino acids in a polypeptide chain
28
Secondary structure of a protein
Folding of polypeptide chain, e.g. alpha helix and beta pleated sheets, due to hydrogen bonding between NH group of one amino acid and C=O group of another amino acid.
29
Tertiary structure of a protein
3D folding of a polypeptide chain due to interactions between amino acid R groups, forming hydrogen bonds, ionic bonds and disulphide bridges
30
Quaternary structure of a protein
More than one polypeptide chain which is formed by interactions between polypeptides- hydrogen bonds, ionic bonds, disulphide bridges.
31
Test for proteins
- Add biuret reagent (sodium hydroxide + copper (II) sulphate)
- If proteins are present in the sample, the solution goes from blue to purple.
32
Induced fit model of enzyme action
- Substrate binds to (not completely complementary) active site of enzyme
- Causing the active site to change shape slightly so it is complementary to its substrate
- So enzyme-substrate complex forms
- Causing bonds in substrate to bend / distort, lowering activation energy
33
Basic function of DNA
Holds genetic information which codes for polypeptides
34
Basic function of RNA
Transfers genetic information from DNA to ribosomes
34
Formation of polynucleotides
Condensation reactions between nucleotides, removing water molecules, between the phosphate group of one nucleotide and pentose sugar (deoxyribose/ribose) of another. Forming a phosphodiester bond
35
Comparison of DNA and mRNA in terms of structure
- DNA pentose sugar is deoxyribose whereas mRNA pentose sugar is ribose
- DNA has the base thymine whereas mRNA has the base uracil
- DNA is double stranded / double helix whereas mRNA is single stranded / single helix
- DNA is long (more nucleotides) whereas mRNA is shorter (fewer nucleotides)
- DNA has hydrogen bonds between complementary base pairs whereas mRNA does not.
36
How does the structure of DNA relate to its functions
- Two strands so both can act as templates for semi-conservative replication
- Hydrogen bonds between bases are weak so strands can be separated for replication
- Complementary base pairing so there's accurate replication
- Many hydrogen bonds between bases so it's a stable / strong molecule
- Double helix with sugar phosphate backbone → protects bases / hydrogen bonds
- Long molecule so it store lots of genetic information (that codes for polypeptides)
- Double helix (coiled) so it's compact
37
Describe DNA replication
- DNA helicase breaks hydrogen bonds between complementary base pairs, unwinding the double helix
- Both strands act as templates
- Free DNA nucleotides are attracted to the exposed bases and join by specific complementary base pairing.
- Hydrogen bonds form between adenine and thymine, and guanine and cytosine.
- DNA polymerase catalyses the formation of phosphodiester bonds between adjacent nucleotides on the new strands through condensation reactions.
- Each new DNA molecule contains one strand from the original / parent molecule and one new strand.
38
Who determined the structure of DNA and came up with the theory of semi-conservative replication
Watson and Crick
39
Describe the work of Meselson and Stahl in validating the Watson-Crick
model of semi-conservative DNA replication
1. Bacteria grown in medium containing heavy nitrogen (15N) so nitrogen is incorporated into DNA bases
- DNA extracted & centrifuged - settles near bottom, as all DNA molecules contain 2 ‘heavy’ strands
2. Bacteria transferred to medium containing light nitrogen (14N) and allowed to divide once
- DNA extracted & centrifuged - settles in middle, as all DNA molecules contain 1 original ‘heavy’ and 1 new ‘light’ strand
3. Bacteria in light nitrogen (14N) allowed to divide again
- DNA extracted & centrifuged - half settles in middle, as contains 1 original ‘heavy’ and 1 new ‘light’ strand; half settles near top, as contains 2 ‘light’ strands
40
Describe the structure of ATP
Ribose bound to adenine and 3 phosphate groups - nucleotide derivative
41
Describe how ATP is broken down
- ATP ---> ADP + Pi
- Hydrolysis reaction using a water molecule, catalysed by ATPase enzymes, e.g. ATP hydrolase.
42
Uses of ATP hydrolysis in cells
- Coupled to energy requiring reactions within cells (releases energy) e.g. active transport, protein synthesis.
- Inorganic phosphate that is released can be used to phosphorylate other compounds, making them more reactive.
43
Describe how ATP is made
- ADP + Pi ---> ATP
- Condensation reaction, removing a water molecule, catalysed by ATP synthase during respiration or photosynthesis.
44
How does the properties of ATP make it a suitable immediate source of energy for cells
- Releases energy in relatively small amounts / little energy is lost as heat
- Single reaction / one bond hydrolysed to release energy so immediate release of energy
- Cannot pass out of the cell
45
Importance of water being a metabolite
Used in condensation / hydrolysis / photosynthesis / respiration
46
Importance of water being a solvent
- Allows metabolic reactions to occur
- Allows transport of substances, e.g. nitrates in xylem, urea in blood
47
Importance of water having a high specific heat capacity
Water buffers changes in temperature as it can gain / lose a lot of energy without changing temperature so...:
- Good and stable habitat for aquatic animals as temperature is more stable than land
- Helps organisms maintain a constant internal body temperature
48
Importance of water having a high latent heat of vaporisation
- Allows effective cooling va evaporation of a small volume of water, e.g. sweat, so helps organisms maintain a constant internal body temperature
49
Importance of water having strong cohesion between water molecules
- Supports columns of water in tube-like transport cells of plants, e.g. transpiration stream through xylem in plants
- Produces surface tension where water meets air, support small organisms to walk on water
