Topic 1 - Biological Molecules Flashcards
(78 cards)
1
Q
What are monomers and polymers
A
- Monomers = smaller repeating
units/molecules from which larger molecules/polymers are made - Polymers = molecules made from many identical/similar monomers
2
Q
What happens in condensation and hydrolysis reactions
A
- Condensation = 2 molecules join together - forming a chemical bond - releasing a water molecule
- Hydrolysis = 2 molecules separated - breaking a chemical bond - using a water molecule
3
Q
Examples of polymers and the monomers they are made from
A
- Polynucleotide (DNA/RNA) - made of nucleotides
- Polysaccharide (starch) - made of monosaccharides
- Polypeptide (protein) - made of amino acids
4
Q
What are monosaccharides - 3 common examples
A
Monomers from which larger carbohydrates are made
Glucose, fructose, galactose
5
Q
Structure of α-glucose
A
draw it out - OH below C1 starting from after O
6
Q
Structure of β glucose
A
draw it out - OH above C1 starting from after O
7
Q
Differences between structure of α-glucose and β glucose
A
- Isomers = same molecular formula but differently arranged atoms
- OH group is below carbon 1 in α-glucose but above carbon 1 in β glucose
8
Q
What are disaccharides and how are they formed
A
- 2 monosaccharides joined together with a glycosidic bond
- Formed by condensation reaction - releasing a water molecule
9
Q
List 3 common disaccharides and monosaccharides they’re made from
A
- Maltose - glucose + glucose
- Sucrose - glucose + fructose
- Lactose - glucose + galactose
10
Q
Draw a diagram to show how 2 monosaccharides join together
A
11
Q
What are polysaccharides and how do they form
A
- Many monosaccharides join together with glycosidic bonds
- Formed by many condensation reactions - releasing many water molecules
12
Q
Basic function and structure of starch
A
- Starch = energy store in plant cells
- polysaccharide of α-glucose - some have 1,4 - glycosidic bonds so is unbranched (amylose) - some have 1,4 and 1.6-glycosidic bonds so are branched (amylopectin)
13
Q
Basic function and structure of glycogen
A
- Glycogen = energy store in animal cells
- polysaccharide of α-glucose - 1,4 and 1.6-glycosidic bonds so are branched
14
Q
How structure of starch (amylose) relates to its function
A
- Helical -> compact for storage in cell
- Large insoluble polysaccharide molecule -> cant leave cell / cross cell membrane
- Insoluble in water -> water potential of cell not affected so no osmotic effect
15
Q
How structure of glycogen (starch and amylopectin) relates to its function
A
- Branched -> compact/fit more molecules in a smaller area
- Branched -> more ends for faster hydrolysis -> release glucose for respiration to make ATP for energy release
- Large insoluble polysaccharide molecule -> cant leave cell / cross cell membrane
- Insoluble in water -> water potential of cell not affected so no osmotic effect
16
Q
Basic function and structure of cellulose
A
- Cellulose = provides strength and structural support to plant/algal cell walls
- Polysaccharide of β glucose - 1,4 glycosidic bonds so form straight,unbranched chains - chains linked in parallel by hydrogen bonds - forms microfibrils
17
Q
How structure of cellulose relates to its function
A
- Every other β glucose molecule is inverted in a long straight unbranched chain
- Many hydrogen bonds link these parallel strands (crosslinks) - forms microfibrils which are strong fibres
- Hydrogen bonds are stronger in high numbers - provides strength to plant cell walls
18
Q
Describe test for reducing sugars
A
Reducing sugars = monosaccharides, maltose, lactose
1 - add benedict’s solution (blue) to sample
2 - heat in boiling water bath
3 - positive result = green/yellow/orange/red precipitate (increasing quantity of sugar)
19
Q
Describe test for non reducing sugars
A
Non reducing sugars = sucrose
1 - do benedict’s test - should stay blue/negative
2 - heat in boiling water bath with acid (hydrolyse into reducing sugars)
3 - neutralise with alkali (sodium bicarbonate)
4 - heat in boiling water bath with benedict’s solution
5 - positive result = green/yellow/orange/red precipitate (increasing quantity of sugar)
20
Q
Suggest a method to measure the amount of sugar in a solution
A
Carry out benedict’s test - filter and dry precipitate - find mass
21
Q
Suggest another method to measure amount of sugar in a solution
A
1 - Make sugar solutions of known concentrations (eg. dilution series)
2 - Heat a set volume of each sample with a set volume of Benedict’s solution for the same time
3 - Use colorimeter to measure absorbance (of light) of each known concentration
4 - Plot calibration curve - concentration on x axis, absorbance on y axis and draw line of best fit
5 - Repeat Benedict’s test with unknown sample and measure absorbance
6 - Read off calibration curve to find concentration associated with unknown sample’s absorbance
22
Q
Describe biochemical test for starch
A
1 - add iodine dissolved in potassium iodide (orange/brown) and shake/stire
2 - positive result = blue/black
23
Q
Name 2 groups of lipids
A
Triglycerides and phospholipids
24
Q
Describe structure of fatty acid (RCOOH)
A
- Variable R-group - hydrocarbon chain (may be saturated or unsaturated)
- COOH - carboxyl group
25
Describe difference between saturated and unsaturated fatty acids
- 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 (bend/kink)
26
Describe how triglycerides form and draw it out
1 glycerol molecule + 3 fatty acids - 3 condensation reactions - removing 3 water molecules - forming 3 ester bonds
27
How properties of triglycerides are related to their structure
- Function = energy storage
- High ratio of C-H bonds to carbon atoms in hydrocarbon chain - used in respiration to release more energy than the same mass of carbohydrates
- Hydrophobic/non polar fatty acids so insoluble in water (clump together as droplets, tails inwards) - no effect on water potential of cell (can be used for waterproofing)
28
Difference between structure of triglycerides and phospholipids
One of the fatty acids of a triglyceride is substituted by a phosphate containing group
29
Describe how properties of phospholipids relate to their structure
- Function = form a bilayer in cell membrane - allow diffusion of non polar lipid soluble or very small substances - restrict movement of polar water soluble substances
- Phosphate heads are hydrophilic -> attracted to water so point to water either side of membrane
- Fatty acid tails are hydrophobic -> repelled by water so point away from water to interior of membrane
30
Describe test for lipids
1 - add ethanol - shake to dissolve lipids - add water
2 - positive result = milky white emulsion
31
Describe general structure of amino acid - draw it out
COOH = carboxyl group
R = variable side group/chain
H2N = amine group
32
How many amino acids are common in all organisms - how do they vary
20 amino acids common in all organisms - differ in their side group R
33
Describe how amino acids join together
- Condensation reaction - removing a water molecule - between carboxyl group of one and amine group of another - forming a peptide bond
34
What are dipeptides and polypeptides?
- Dipeptide = 2 amino acids joined together
- Polypeptide = many amino acids joined together
- Functional protein may contain one or more polypeptides
35
Describe the primary structure of a protein
Sequence of amino acids in a polypeptide chain - joined by peptide bonds
36
Describe the secondary structure of a protein
- Folding (repeating patterns) of polypeptide chain (alpha helix / beta pleated sheets)
- Due to hydrogen bonding between amino acids
- Between NH group of one amino acid and C=O group of another
37
Describe the tertiary structure of a protein
- 3D folding of polypeptide chain
- Due to interactions between amino acid R groups (dependa on sequence of amino acids)
- Forming hydrogen bonds, ionic bonds and disulfide bridges
38
Describe the quaternary structure of a protein
- More than one polypeptide chain
- Formed by interactions between polypeptides (hydrogen bonds, ionic bonds, disulfide bridges)
39
Describe test for proteins
1 - add biuret reagent (sodium hydroxide + copper (II) sulphate)
2 - positive result = purple/lilac colour (indicates presence of peptide bonds)
40
How do enzymes act as biological catalysts
- Each enzyme lowers activation energy of the reaction it catalyses
- Speeds up rate of reaction
41
Describe induced fit model of enzyme action
1 - substrate binds to (not completely complementary) active site of enzyme
2 - causes active site to slightly change shape so it is complementary to its substrate
3 - enzyme substrate complexes form
4 - bonds in substrate bend/distort - lowers activation energy
42
Describe how models of enzyme action have changed over time
- Initially lock and key which is now outdated (active site is a fixed shape/complementary to one substrate)
- Now induced fit model
43
Explain specificity of enzymes
- Specific tertiary structure determines shape of active site -> depends on sequence of amino acids (primary structure)
- Active site if complementary to a specific substrate
- Only this substrate can bind to active site, inducing fit, forming enzyme substrate complex
44
Describe and explain effect of enzyme concentration on rate of enzyme controlled reactions
- As enzyme concentration increases, rate of reaction increases
-> Enzyme concentration = limiting factor (excess substrate)
-> More enzymes so more active sites are available
->So more enzyme-substrate complexes form
- At a certain point, rate of reaction stops increasing / levels off
-> Substrate concentration = limiting factor (all substrates in use)
45
Describe & explain effect of substrate concentration on rate of enzyme controlled reactions
- As substrate concentration increases, rate of reaction increases
-> Substrate concentration = limiting factor (too few substrate molecules to occupy all active sites)
-> More enzyme-substrate complexes form
- At a certain point, rate of reaction stops increasing / levels off
-> Enzyme concentration = limiting factor
-> As all active sites saturated / occupied (at a given time)
46
Describe and explain the effect of temperature on the rate of enzyme-controlled reactions
- As temperature increases to optimum, rate of reaction increases
-> More kinetic energy
-> So more enzyme-substrate complexes form
- As temperature exceeds optimum, rate of reaction decreases
-> Enzymes denature - tertiary structure and active site change shape
-> As hydrogen / ionic bonds break
-> So active site no longer complementary
-> So fewer enzyme-substrate complexes form
47
Describe and explain the effect of pH on the rate of enzyme-controlled reactions
- As pH increases / decreases above / below an optimum, rate of reaction decreases
-> Enzymes denature - tertiary structure and active site change shape
-> As hydrogen / ionic bonds break
-> So active site no longer complementary
-> So fewer enzyme-substrate complexes form
48
Describe and explain the effect of concentration of competitive inhibitors on the rate of enzyme-controlled reactions
- As concentration of competitive inhibitor increases, rate of reaction decreases
-> Similar shape to substrate
-> Competes for / binds to / blocks active site
-> So substrates can’t bind
-> So fewer enzyme-substrate complexes form
- Increasing substrate concentration reduces effect of inhibitors (dependent on relative concentrations of substrate and inhibitor)
49
Describe and explain the effect of concentration of non-competitive inhibitors on the rate of enzyme-controlled reactions
- As concentration of non-competitive inhibitor increases, rate of reaction decreases
-> Binds to site other than the active site (allosteric site)
-> Changes enzyme tertiary structure / active site shape
-> So active site no longer complementary to substrate
-> So substrates can’t bind
-> So fewer enzyme-substrate complexes form
= Increasing substrate concentration has no effect on rate of reaction as change to active site is permanent
50
Describe basic functions of DNA and RNA in living cells
- DNA -> holds genetic information which codes for polypeptides (proteins)
- RNA -> transfers genetic information from DNA to ribosomes
51
Draw and label DNA and RNA nucleotide
51
Name 2 types of molecules from which ribosomes are made
RNA and proteins
52
Differences between DNA and RNA nucleotide
DNA -> pentose sugar is deoxyribose
RNA -> pentose sugar is ribose
DNA -> base can be thymine
RNA -> base can be uracil
53
How do nucleotides join together to form polynucleotides
- Condensation reactions - removing water molecules
- Between phosphate group of one nucleotide and pentose sugar of another
- Forming phosphodiester bonds
54
Why did scientists initially doubt that DNA carried genetic code
Relative simplicity of DNA -> chemically simple molecule with few components
55
Structure of (messenger) RNA
- Polynucleotide
- Each nucleotide made of ribose, phosphate group, nitrogen containing organic base
- Bases = uracil adenine cytosine and guanine
- Phosphodiester bonds join adjacent nucleotides - single helix structure
55
Structure of DNA
- Polynucleotide
- Each nucleotide made of deoxyribose, phosphate group, nitrogen containing organic base
- Phosphodiester bonds join adjacent nucleotides
- 2 polynucleotide chains are held together by hydrogen bonds between specific complementary base pairs - AT CG
- Double helix structure
56
Compare and contrast structure of DNA and (messenger) RNA
DNA -> pentose sugar is deoxyribose
RNA -> pentose sugar is ribose
DNA -> base thymine
RNA -> base uracil
DNA -> double stranded/double helix
RNA -> single stranded/single helix
DNA -> longer (many nucleotides)
RNA -> shorter (fewer nucleotides)
57
Suggest how you can use incomplete information about the frequency of bases on DNA strands to find the frequency of other bases
% of adenine in strand 1 = % of thymine in strand 2
% of guanine in strand 1 = % of cytosine in strand 2
58
Suggest how structure of DNA relates to its functions
- Two strands -> both can act as templates for semi conservative replication
- Hydrogen bonds between bases are weak -> strands can be separated for replication
- Complementary base pairing -> accurate replication
- Many hydrogen bonds between bases -> stable/strong molecule
- Double helix (coiled) -> compact
59
Why is semi conservative replication important
Ensures genetic continuity between generations of cells
60
Describe process of semi conservative DNA replication
1 - DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix
2 - Both strands act as templates
3 - Free DNA nucleotides are attracted to exposed bases and join by specific complementary base pairing
4 - Hydrogen bonds form between adenine-thymine and guanine-cytosine
5 - DNA polymerase joins adjacent nucleotides on new strand by condensation reactions
6 - Forming phosphodiester bonds
Semi conservative = each new DNA molecule consists of one original/template strand and one new strand
61
Use enzyme action to suggest why DNA polymerase moves in opposite directions along DNA strands
- DNA has antiparallel strands
- Shapes/arrangements of nucleotides on two ends are different
- DNA polymerase is an enzyme with a specific shaped active site
- So can only bind to substrate with complementary shape (phosphate end of developing strand)
62
Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication
Watson and Crick
63
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 is transferred into medium containing light nitrogen (14N) and is allowed to divide once - DNA is 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 it contains 1 original heavy strand and 1 new light strand - half settles near top as it contains 2 light strands
64
What is ATP?
Adenosine triphosphate
65
Describe the structure of ATP
- Ribose bound to a molecule of adenine (base) and 3 phosphate groups
- Nucleotide derivative (modified nucleotide)
66
Give 2 ways in which the hydrolysis of ATP is used in cells
- Coupled to energy requiring reactions within cells (releases energy) - eg active transport, protein synthesis
- Inorganic phosphate released can be used to phosphorylate (add phosphate) other compounds making them more reactive
67
Describe how ATP is broken down
- ATP + water -> ADP (adenosine diphosphate) + Pi (inorganic phosphate)
- Hydrolysis reaction, using a water molecule
- Catalysed by ATP hydrolase (enzyme)
68
Describe how ATP is re-synthesised in cell
- ADP + Pi -> ATP + water
- Condensation reaction, removing a water molecule - catalysed by ATP synthase
- During respiration and photosynthesis
69
Suggest how properties of ATP make it a suitable immediate source of energy for cells
- Releases energy in relatively small amounts/little energy lost as heat
- Single reaction/one bond hydrolysed to release energy (so immediate release)
- Cannot pass out of cell
70
Explain how hydrogen bonds occur between water molecules
- Water is polar molecule
- Slightly negatively charged oxygen atoms attract slightly positively charged hydrogen atoms of other water molecules
71
Explain 5 properties of water that are important in biology
- Metabolite -> used in condensation/hydrolysis/photosynthesis/respiration
- Solvent -> allows metabolic reactions to occur faster in solution
-> allows transport of substances eg- nitrates in xylem, urea in blood
- Relatively high specific capacity -> buffers changes in temperature as it can gain/lose a lot of heat/energy without changing temperatures -> good habitat for aquatic organisms as temperature more stable than land
-> helps organisms maintain a constant internal body temperature
- Relatively large latent heat of vaporisation -> allows effective cooling via evaporation of a small volume - so helps organisms maintain a constant internal body
temperature
Strong cohesion between water molecules -> supports columns of water in tube like transport cells of plants (eg, transpiration stream in xylem)
-> produces surface tension where water meets air, supports small organisms to walk on water
72
Where are inorganic ions found in the body
- In solution in cytoplasm and body fluid, some in high concentration and others in lower concentration
73
Role of hydrogen ions
- Maintain pH levels in the body -> high concentration = acidic/low pH
- Affects enzyme rate of reaction as it can cause enzymes to denature
74
Role of iron ions
- Component of haem group of haemoglobin
- Allows oxygen to bind/associate for transport as oxyhaemoglobin
75
Role of sodium ions
- Involved in co transport of glucose/amino acids into cells
- Involved in action potentials in neurons
- Affects water potential of cells/osmosis
76
Role of phosphate ions
- Component of nucleotides, allows phosphodiester bonds to form in DNA/RNA
- Component of ATP, allowing energy release
- Phosphorylates other compounds to make them more reactive
- Hydrophilic part of phospholipids allowing a bilayer to form
