Biological Molecules Topic 1 Flashcards
(53 cards)
1
Q
Define the terms monomer and polymer
A
Monomer: small units from which larger molecules are made.
Polymer: large molecule made up of many similar / identical monomers joined together.
2
Q
Give three examples of a monomer and 3 examples of a
polymer
A
Monomer:
Monosaccharide
Amino Acid
Nucleotide
Polymer:
Polysaccharide
Polypeptide
DNA/RNA
3
Q
What is a condensation reaction?
A
A condensation reaction:
- Joins 2 molecules together.
- Elimination of a water molecule.
- Formation of a chemical bond e.g. glycosidic bond.
4
Q
What is a hydrolysis reaction?
A
A hydrolysis reaction:
- Separates 2 molecules.
- Addition of a water molecule.
- Breakage of a chemical bond e.g. glycosidic bond.
5
Q
What are Monosaccharides? Give 3 examples.
A
Monosaccharides are the monomers from which larger carbohydrates
are made.
- E.g. glucose, galactose and fructose.
6
Q
How are disaccharides formed? Explain using the examples:
maltose, sucrose and lactose.
A
- Disaccharides are formed by the condensation of 2 monosaccharides.
- E.g. maltose, sucrose and lactose
- Glucose + glucose = maltose
- Glucose + fructose = sucrose
- Glucose + galactose = lactose
7
Q
Define the term Isomer
A
Isomer: when molecules have the same molecular formula but the atoms are arranged differently.
8
Q
How many isomers does glucose have?
A
Glucose has 2 isomers, alpha-glucose and beta-glucose.
9
Q
What are the differences between the 2 isomers of glucose?
A
Difference in structures:
- Alpha-glucose: OH groups below C1 and below C4.
- Beta-glucose: OH groups above C1 and below C4 i.e. position of
OH on C1 is reversed compared to alpha glucose.
10
Q
How are polysaccharides formed? Name 3 examples of
polysaccharides.
A
Polysaccharides are formed by the condensation of many glucose
units. Examples include:
Starch
Glycogen
Cellulose
11
Q
How is the structure of glycogen related to its function?
A
Function: energy store in animal cells.
- Structure:
- Polysaccharide of alpha-glucose.
- C1-C4 and C1-C6 glycosidic bonds so branched.
- Structure related to function:
- Branched; can be rapidly hydrolysed to release glucose for respiration to provide energy.
- Large polysaccharide molecule; can’t leave cell.
- Insoluble in water; water potential of cell not affected i.e. no osmotic effect.
12
Q
How is the structure of starch related to its function?
A
- Function: energy store in plant cells.
- Structure:
- Polysaccharide of alpha-glucose.
- Made of amylose and amylopectin.
- C1-C4 glycosidic bonds in amylose; unbranched.
- C1-C4 and C1-C6 glycosidic bonds in amylopectin; branched.
- Structure related to function:
- Helical; compact for storage in cell.
- Large polysaccharide molecule; can’t leave cell.
- Insoluble in water; water potential of cell not affected i.e. no osmotic effect.
13
Q
How is the structure of cellulose related to its function?
A
Function: provides strength and structural support to plant cell walls.
Structure related to function:
. Every other beta-glucose molecule is inverted in a long, straight, unbranched chain.
. Many hydrogen bonds link parallel strands (crosslinks) to form micro
fibrils (strong fibres).
. H bonds are strong in high numbers.
. Provides strength and structural support to plant cell walls.
14
Q
Which sugars are reducing sugars and which are non-reducing
sugars? What is the test for them?
A
Benedicts Test can detect reducing and non reducing sugars
Reducing Sugars:
- All monosaccharides e.g. glucose
- Some disaccharides e.g. maltose/lactose
Non-Reducing Sugar:
- No monosacharides
- Some disaccharides e.g. sucrose
15
Q
Describe how to carry out the Benedict’s test for reducing sugars
A
Benedict’s test for reducing sugars:
- Add benedict’s reagent (blue) to food sample.
- Heat in a boiling water bath.
- Positive = green / yellow / orange / red precipitate (reducing sugar
present).
* If negative result (Benedicts reagent doesn’t change colour) then test for non-reducing sugar.
16
Q
Describe how to carry out the Benedict’s test for non-reducing
sugars
A
Benedict’s test for non-reducing sugars:
- Add an equal volume of sample and dilute hydrochloric acid to
hydrolyse the sugar. - Heat in a boiling water bath.
- Neutralise with sodium bicarbonate.
- Carry out normal benedict’s test.
- Non-reducing sugar present = green / yellow / orange / red precipitate.
17
Q
Explain how the concentration of glucose in a sample can be
determined.
A
- Produce a dilution series of glucose solutions of known concentrations.
- Perform a Benedict’s test on each sample (use same amount of
solution for each test) and remove any precipitate (e.g. by
centrifuging). - Using a colorimeter, measure the absorbance of each sample to
establish a calibration curve. - Repeat with unknown sample and compare the absorbance to the
calibration curve to determine glucose concentration.
18
Q
Describe the test for starch
A
- Add iodine dissolved in potassium iodide to solution and shake/stir.
- Blue-black colour = starch present.
19
Q
Name 2 groups of lipid
A
Triglycerides and phospholipids are 2 groups of lipid.
20
Q
Describe how triglycerides are formed
A
Triglycerides are formed by the condensation of:
* 1 molecule of glycerol and 3 molecules of fatty acid.
* A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.
* 3 condensation reactions; therefore 3 ester bonds present.
21
Q
Describe the differences between saturated and unsaturated fatty
acids
A
- The R-group of a fatty acid may be saturated or unsaturated.
- Saturated: no C=C double bonds in hydrocarbon chain; all carbons
fully saturated with hydrogen. - Unsaturated: one or more C=C double bonds in hydrocarbon chain.
22
Q
Describe the structure of a phospholipid
A
In phospholipids, one of the fatty acids of a triglyceride is substituted by
a phosphate-containing group.
23
Q
Describe the emulsion test for lipids
A
Add ethanol (alcohol) and shake (to dissolve lipids).
* Then add water.
* Positive: milky/cloudy white emulsion.
Any solid food samples must be crushed/ground up as the first step.
24
Q
Describe how the properties of triglycerides relate to their
structure.
A
- Triglycerides: energy storage molecules / energy source.
- High ratio of C-H bonds to C atoms in hydrocarbon tail.
- Release more energy than same mass of carbohydrates.
- Insoluble in water (clump together as droplets)
- No effect on water potential of cell i.e. no osmotic effect.
25
Describe how the properties of triglycerides relate to their
structure.
Phospholipids: form cell membrane (phospholipid bilayer); allowing
movement of non-polar / lipid soluble / small molecules down a
concentration gradient.
* Phosphate heads are polar / hydrophilic.
* Attracted to water → orient to aqueous environment either side of
membrane.
* Fatty acid tails are non-polar / hydrophobic.
* repelled by water → orient to interior of membrane.
26
Describe what amino acids are. Draw and label the general
structure of an amino acid.
Amino acids are the monomers from which proteins are made.
* The general structure of an amino acid:
* NH2 represents an amine group.
* COOH represents a carboxyl group.
* R represents a variable side chain.
27
Describe the formation and product(s) of a peptide bond. Draw
and label the position of the bond using the general structure of
an amino acid.
A condensation reaction between 2 amino acids forms a peptide
bond.
* Dipeptides are formed by the condensation of two amino acids.
* Polypeptides are formed by the condensation of many amino acids.
* A functional protein may contain one or more polypeptides.
28
Describe the different structural levels of proteins and the bonds
present at each level.
Primary (1°) structure: Sequence of amino acids in a polypeptide chain
(joined by peptide bonds).
- Secondary (2°) structure: Hydrogen bonding between amino acids
(between the carbonyl O of one amino acid and the amino H of another).
. This causes the polypeptide chain to fold into a repeating pattern e.g.
alpha helix or beta pleated sheet
- Tertiary (3°) structure: Overall 3D structure of a polypeptide.
Held together by interactions between the amino acid side chains (R
groups): Ionic bonds; Disulfide bridges; Hydrogen bonds
- Quaternary (4°) structure: Some proteins are made of 2+ polypeptide
chains.
. Also held together by more hydrogen, ionic and disulfide bonds.
29
Describe the test for proteins.
The biuret test for proteins:
* Add biuret solution: sodium hydroxide + copper (II) sulfate
* Protein present: purple colour (no protein present – stay blue).
* Detects presence of peptide bonds.
30
Describe the nature and function of enzymes. Draw and label
the free energy graph for reactions with and without enzymes.
Enzymes are biological catalysts; they catalyse a wide range of intracellular (within cells) and extracellular (outside cells) reactions that determine structures and functions from cellular to whole-organism level.
Each enzyme lowers the activation energy of the reaction it catalyses (see diagram) → speed up rate of reaction
31
Describe the old and current models of enzyme action.
Lock and Key
- Old, outdated
- Active site is a fixed shape/complementary to one substrate
- After a successful collision, an enzyme substrate complex forms leading to a reaction
Induced Fit Model
- Recent, accepted
1) Before reaction, enzyme active site not completely complementary to substrate/doesnt fit substrate
2) Active site shape changes as substrate bonds and an enzyme substrate complex forms
3) This stresses/distorts bonds in substrate leading to a reaction
32
Describe the specificity of an enzyme with regards to its tertiary
structure.
The properties of an enzyme relate to the tertiary structure of its active site and its ability to combine with complementary substrate(s) to form an enzyme-substrate complex.
Enzymes have a specific shaped tertiary structure and active site - Sequence of amino acids (primary structure) determines tertiary structure.
Active site is complementary to a specific substrate.
Enabling only this substrate to bind to the active site (induce fit)
→ enzyme-substrate complex.
33
Explain how enzyme concentration affects the rate of reaction.
- Increasing enzyme conc. → rate of reaction increases.
- Enzyme conc. = limiting factor (substrate in excess).
- More enzymes → more available active sites.
- More successful E-S collisions and E-S complexes.
- At a certain point, rate of reaction plateaus.
- Substrate conc. = limiting factor (all substrates in use).
34
Explain how substrate concentration affects the rate of an enzyme-catalysed reaction.
Increasing substrate conc. → rate of reaction increases.
. Substrate concentration = limiting factor (too few enzyme molecules to occupy all active sites).
. More successful E-S collisions and E-S complexes.
. At a certain point, rate of reaction plateaus.
. Enzyme conc. = limiting factor (all active sites saturated; excess substrate).
35
Explain how temperature affects the rate of an enzyme-catalysed reaction.
. Increasing temp. up to optimum → rate of reaction increases.
. Increase in kinetic energy.
. More successful E-S collisions and E-S complexes.
. Increasing temp. above optimum → rate of reaction falls.
. Enzymes denature; tertiary structure and active site change shape (hydrogen and ionic bonds break).
. Fewer E-S collisions and E-S complexes (substrate no longer binds to active site).
. Rate of reaction 0 when all enzymes denatured.
36
Explain how pH affects the rate of an enzyme-catalysed reaction.
. pH above/below optimum pH → rate of reaction decreases.
. Enzymes denature; tertiary structure and active site change shape (hydrogen and ionic bonds break).
. Complementary substrate no longer binds/fits to active site.
. Fewer E-S collisions and E-S complexes.
37
Explain how concentration of competitive and non-competitive
inhibitors affects the rate of an enzyme-catalysed reaction.
. Competitive inhibitors decrease rate of reaction.
. Similar shape to substrate.
. Competes for / binds to / blocks active site so substrates can’t bind.
. Fewer E-S complexes.
. Increasing substrate conc. reduces effect of inhibitor (level of inhibition dependent on relative concs. of substrate and inhibitor).
. Non-competitive inhibitors decrease rate of reaction.
. Binds to site away from the active site (allosteric site).
38
What are the functions of DNA and RNA in living cells?
. Deoxyribonucleic acid (DNA) holds genetic information.
. Ribonucleic acid (RNA) transfers genetic information from DNA to ribosomes.
39
Draw and Label the structure of DNA and RNA Nucleotides
DNA nucleotide:
Phosphate group
Deoxyribose
Nitrogen Containing Base (Adenine, Thymine, Guanine, Cytosine)
RNA nucleotide:
Phosphate group
Ribose
Nitrogen Containing Base (Adenine, Uracil, Guanine, Cytosine)
40
What are the differences between DNA and RNA structure?
DNA nucleotides have pentose sugar deoxyribose whereas RNA nucleotides have ribose.
DNA nucleotides can have thymine whereas RNA nucleotides have uracil instead.
DNA molecules are double stranded whereas RNA molecules are single stranded.
DNA is longer whereas RNA is shorter.
41
Compare the structure and bonding between DNA & RNA polymers?
DNA: 2 strands joined in anti-parallel held together by hydrogen
bonds between specific complementary base pairs – AT (2 H
bonds) and CG (3 H bonds).
A condensation reaction between 2 nucleotides forms a phosphodiester bond.
42
Describe how the structure of DNA is related to its function.
Large number of (individually) weak hydrogen bonds between complementary bases on different strands → stable / strong molecule and can be unzipped for replication.
Double helix (with sugar phosphate backbone) → protects bases / hydrogen bonds.
Long molecule → store lots of (genetic) information (can code for sequence of amino acids in the primary structure of a protein).
Double stranded → semi-conservative replication can occur as both strands can act as templates.
Complementary base pairing (A-T, C-G) → accurate replication / identical copies can be made
Double helix (coiled) → compact.
43
Describe the process of DNA replication.
1) DNA Helicase breaks hydrogen bonds between bases, unwinds double helix.
🡪 Two strands which both act as templates.
2) Free floating DNA nucleotides attracted to exposed bases via specific
complementary base pairing, hydrogen bonds form (adenine-guanine;
guanine-cytosine).
3) DNA polymerase joins adjacent nucleotides on new strand by condensation, forming phosphodiester bonds (🡪 sugar phosphate backbone).
🡪 Replication is semi-conservative – each new strand formed contains one original / template strand and one new strand.
🡪 Ensures genetic continuity between generations of cells.
44
Describe the experiment carried out by Meselson & Stahl and how it was used to provide evidence for semi-conservative replication.
Bacteria grown in a nutrient solution containing heavy nitrogen (15N) for several generations.
Nitrogen incorporated into bacterial DNA bases.
Bacteria then transferred to a nutrient solution containing light nitrogen (14N) and allowed to grow and divide twice.
During this process, DNA from different samples of bacteria was extracted, suspended in a solution in separate tubes and spun in a centrifuge.
45
Give the basic equation for ATP hydrolysis and name the enzyme
involved in this process.
ATP → ADP + Pi
Catalysed by the enzyme ATP hydrolase.
46
What occurs during ATP hydrolysis and what does this result in?
Bonds between inorganic phosphate groups are high energy bonds so by breaking one of these bonds a small amount of energy is released.
Can be coupled to energy requiring reactions within cells, to provide energy for e.g. active transport, protein synthesis.
The inorganic phosphate released can be used to phosphorylate other
compounds e.g. glucose, often making them more reactive (i.e. lowers
activation energy).
47
Give the basic equation for ATP condensation and name the
enzyme involved in this process.
ADP + Pi 🡪ATP
Catalysed by the enzyme ATP synthase.
48
When does ATP condensation occur?
Happens during respiration or photosynthesis
49
Describe the properties of ATP that make it a suitable immediate
energy source.
ATP releases energy in small, manageable amounts (so no energy
wasted).
Only one bond is hydrolysed (single reaction) to release energy
(which is why energy release is immediate).
50
Describe the structure and bonding present in water.
Water is a covalent compound made up of 2 hydrogen atoms + 1 oxygen.
Oxygen has a slight negative charge and hydrogen atoms have a slight positive charge = (di)polar.
Hydrogen bonds (attractive force between opposite charges) form between water molecules causing them to ‘stick together’.
51
Properties of Water
1) Cohesion between water molecules
- water molecules stick together - polar molecules - hydrogen molecules form between molecules
- produces surface tension on the surface of the water, allowing pond skaters to walk on the water
2) Water is a metabolite
- water is reactive
- hydrolysis requires H2O to break a bond, e.g amino acids joined by condensation reactions to form polypeptides
3) Universal Solvent
- water = polar molecule - positive end of a water molecule attracted to a negative ion whilst the negative end is attracted to a positive ion - ions and polar molecules can be dissolved
- water can dissiove other substances e.g. oxygen, urea, inorganic ions -> metabolic reactions take place in solution, causing the random movement of molecules increasing so the reate of successful collisions increase
4) High specific Heat Capacity
- Water absorbs a large amount of heat before its temperature changes
- water acts as a buffer against temperature fluctuations, which is important as it helps to maintain a constant internal body temperature
5) Large Latent Heat of Vaporisation
- Water absorbs a large amount of heat before it evaporates.
- evaporating water is a method of cooling organisms to help eachother maintain a constant body temperature
52
State where inorganic ions can be found in the body.
- Occur in solution in the cytoplasm and body fluids of organisms.
- Some in high concentrations and others in very low concentrations.
53
What are the 4 key inorganic ions and what role do they have in the body?
PHOSPHATE IONS – PO43-
Attached to other molecules as a phosphate group.
Phosphate ions form the phosphate groups of DNA/RNA nucleotides.
Enables nucleotides to join together – phosphodiester bonds form.
Phosphate ions form the phosphate groups of ATP - Breaking the bonds between the phosphate groups in ATP releases energy.
SODIUM IONS – Na+
Co transport of glucose and amino acids across cell membranes.
HYDROGEN IONS – H+
Maintain pH levels in the body. * Too much H+ = acidic (low pH).
Too little H+ = alkaline (high pH).
Affects rate of enzyme controlled reactions as can cause enzymes to denature.
IRON IONS – Fe2+
Component of (haem group of) haemoglobin which is contained in red blood cells.
Transports oxygen around the body – oxygen temporarily binds to it so it becomes Fe3+.
