T1: Biological Molecules Flashcards
1
Q
Define monomer. Give three examples.
A
- is a small , repeating unit from which larger molecules / polymers are made.
- monosaccharides
- amino acids
- nucleotides
2
Q
Define polymer. Give three examples
A
molecules made up of many monomers
- polysaccharides
- proteins
- DNA/RNA
3
Q
Describe a condensation reaction.
A
- A chemical bond forms between 2 molecules & a molecule of water is produced
4
Q
Describe a hydrolysis reaction
A
- a water molecule is used to break a chemical bond between 2 molecules
5
Q
Name the 3 (hexose) monosaccharides
A
- glucose
- fructose
- galactose
6
Q
Name the type of bond formed when monosaccharides react.
A
- glycosidic bond
7
Q
Name three disaccharides and what they consist of. Describe how they form.
draw the formation of glycosidic bond between 2 monosaccharides
A
- condensation reaction forms glycosidic bond between 2 monosaccharides
maltose: 2 glucose
sucrose: glucose + fructose
lactose: glucose + galactose
8
Q
what is an isomer
A
- molecules with the
- same molecular formula but differently arranged atoms
9
Q
What is the difference between an alpha glucose and beta glucose molecule?
A
in beta glucose, hydroxyl group on carbon 1 is facing upwards
10
Q
Describe the structure and function of starch
A
- function: storage polymer of alpha glucose in plant cells
- amylose:
- 1,4 glycosidic bonds
- helical so compact
amylopectin: - 1,4 & 1,6 glycosidic bonds
- branched= many terminal ends for hydrolysis into glucose
- insoluble= no osmotic effect on cells / does not affect water potential
- large= does not diffuse out of cells
11
Q
Starch is a carbohydrate often stored in plant cells .
describe and explain four features of starch that make it a good storage molecule (4)
A
Any two from:
1. Insoluble (in water), so doesn’t affect water potential;
2. Branched / coiled / (a-)helix, so makes molecule compact;
3. Polymer of (a-)glucose so provides glucose for respiration;
4. Branched / more ends for fast breakdown / enzyme action;
5. Large (molecule), so can’t cross the cell membrane
12
Q
Describe how the structure of glycogen is related to its function.
A
- main storage polymer of alpha glucose in animal cells
- 1,4 & 1,6 glycosidic bonds
- it has a helix and branched structure and so is compact
- Branched so more ends for faster hydrolysis;
- polymer of Glucose so provides respiratory substrate for energy (release);
- Insoluble so does not affect water potential/osmosis
- Polymer of glucose so easily hydrolysed
13
Q
Suggest how glycogen acts as a source or energy.
A
- hydrolysed to glucose
- glucose is than used in respiration
14
Q
Describe how the structure of glycogen is related to its function. (4)
A
- it has a helix and branched structure and so is compact
- Branched so more ends for faster hydrolysis;
polymer of Glucose so provides respiratory substrate for energy (release); - Insoluble so does not affect water potential/osmosis
alternatives : - Polymer of glucose so easily hydrolysed
15
Q
Describe and explain how the structure of cellulose relates to its function (4)
A
- 1,4 glycosidic bonds
- cellulose is made up of long unbranched straight chains of beta glucose
- which interact to form microfibrils
- the chains of b glucose are joined together by hydrogen bonds
- which provide strength in cell walls
16
Q
Glycogen and cellulose are both carbohydrates.
Describe 4 differences between the structure of a cellulose molecule and a glycogen molecule.
A
- Cellulose is made up of beta glucose monomers and glycogen is made up of alpha glucose monomers
- cellulose molecule has straight chains and glycogen is branched
- cellulose molecule has straight chain and glycogen is coiled.
- glycogen has 1,4 and 1,6 glycosides bonds and cellulose only has 1,4- glycosidic bonds
17
Q
Describe the test for identifying reducing sugars in a food sample
A
- add an equal volume of Benedict’s reagent to a sample
- heat the mixture in an electric water bath for 100°C
- POSITIVE RESULT: colour change from blue to orange & brick-red precipitate forms
Red / orange / yellow / green (colour); Reject Add HCl
18
Q
Describe the Benedict’s test for non-reducing sugars
A
- negative result: Benedict’s reagent remains blue
- hydrolyse non-reducing sugars e.g. sucrose into their monomers by adding 1cm3 of HCl
- heat in a boiling water bath for 5 mins
- neutralise the mixture using sodium carbonate solution
- proceed with the Benedict’s test as usual
19
Q
Suggest a method to measure the quantity of sugar in a solution
A
- carry out benedict’s test as above, then filter and dry precipitate
- find mass/weight
20
Q
Describe a method to identify the concentration of glucose in an unknown solution.
A
- Make sugar solutions of known concentrations (e.g. dilution series)
- Heat a set volume of each sample with a set volume of Benedict’s solution for same time
- Use colorimeter to measure absorbance of light of each known concentration
- Plot calibration cruve - conc on x axis , absorbance on y
- Draw line of best fit. Repeat Benedict’s test with unknown sample and measure absorbance.
- Red off calibration cruve to find conc associated with unknown sample’s absorbance
21
Q
Describe the test for starch
A
- Add iodine solution dissolved in potassium idide.
- Positive result: colour change from orange to blue-black
22
Q
Describe how to test for lipids in a sample
A
- Dissolve solid samples in ethanol
- shake and mix
- THEN add an equal volume of water
- Positive result: milky white emulsion forms
23
Q
Describe the struture of a fatty acid
A
- variable R group - hydrocarbon chain
- -COOH : carboxyl group
24
Q
How do triglycerides form?
draw one
A
- condensation reaction , which removes 3 H20
- between 1 molecule of glycerol and 3 fatty acids
- forms ester bonds. (3)
25
Compare saturated and unsaturated fatty acids
saturated:
- contain only single bonds
- higher melting point = solid at room temp
- straightly packed
unsaturated:
- contain C=C double bonds
- Kinks or bends caused by double bonds, so they can't pack tightly - greater fluidity : leads to
- lower melting point liquid at room temp
26
Describe how a saturated fatty acid differs in molecular structure from an unsaturated fatty acid (2)
- absence of a double bond;
- in the (hydrocarbon) chain;
- unable to accept more hydrogen / saturated with hydrogen;
27
Give two characteristics of triglycerides
- insoluble hydrocarbon chain so no effect on water potential of cells and used for *waterproofing*
- slow conductor of heat: thermal insulation
28
describe the structure and function of phospholipids
- Amphipathic molecule:
- glycerol backbone
- 2 hydrophobic fatty acid tails
- 1 hydrophilic polar phosphate head,
- forms phospholipids bilayer in water = component of membranes
29
Compare phospholipids and triglycerides
| give 4 similarities
- Both contain a glycerol backbone
- Both contain fatty acid chains (long hydrocarbon chains)
- Both are formed by condensation reactions, creating ester bonds
- Both have hydrophobic fatty acid tails
30
Contrast phospholipids and triglycerides
p:
- 2 fatty acids & 1 phosphate group attached
- hydrophilic head & hydrophobic tail
- used primarily in membrane formation
t:
- 3 fatty acids attached
- entire molecule is hydrophobic
- used primarily as a storage molecule
31
Are phospholipids and triglyceride polymers?
- No, they are not made from a small repeating unit
- they are macromolecules
32
Draw the structure of a nucleotide
- a phosphate group attached to a pentose sugar attached to a nitrogen-containing base
33
Name the pentose sugars in DNA & RNA
DNA: deoxribose
RNA: ribose
34
State the role of DNA in living cells
- contains genetic information
- which determines inherited characteristics = influences structure and function of organisms
35
How do polynucleotides form?
- condensation reaction between nucleotides ( sugar - phosphate)
- forms phosphodiester bonds
- leads to sugar - phosphate backbone
36
Describe the structure of DNA (5)
- Polymer of nucleotides;
- Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
- Phosphodiester bonds (between nucleotides);
- Double helix made up of 2 strands held by hydrogen bonds;
- (Hydrogen bonds/pairing) between adenine, thymine andcytosine, guanine;
37
Which bases are purine and which are pyrimidine?
Adenine and Guanine: 2-ring purine bases
Thymine, Cytosine and Uracil: 1-ring pyrimidine bases
38
Name the complementary base pairs in DNA and their hydrogen bonds
Adenine + thymine : 2 H-bonds
Guanine + Cytosine: 3 hydrogen bonds
39
Name the complementary base pairs in RNA
2 H bonds between Adenine + Uracil
3 H bonds between guanine + cytosine
40
Relate the structure of DNA to its functions (6)
- sugar-phosphate backbone & many H-bonds provide stability
- long molecule stores lots of information
- helix is compact for storage in nucleus
- base sequence of triplets codes for amino acids
- double-stranded for semi-conservative replication
- complementary base pairings for accurate replication
- weak H-bonds break so strands separate for replication.
41
Describe the structure of messenger RNA (mRNA)
| give 4 features
- single stranded & linear
- long ribose polynucleotide but shorter than DNA
- contains uracil instead of thymine base
- codon sequence is complementary to exons of 1 gene from 1 DNA strand
42
Relate the structure of messenger RNA to its function
- breaks down quickly so no excess polypeptide forms
- ribosome can move along strand & tRNA can bind to exposed bases
- can be translated into a specific polypeptide by ribosomes
43
Describe the structure of transfer RNA (trna)
- tRNA molecules have a characteristic cloverleaf shape
- are composed of a single strand of RNA with several loop structures.
44
Order DNA, mRNA and tRNA according to increasing length
tRNA
mRNA
DNA
45
Desxribe the difference between a DNA nucleotide and an RNA nucleotide
- deoxyribose sugar vs ribose
- uracil vs thymine
46
Why did scientists initially doubt that DNA carried the genetic code?
- chemically simple molecules with few components
47
Name the two scientists who proposed models of the chemical structure of
DNA and of DNA replication. (1)
- Watson and Crick
48
Why is DNA replication described as semi-conservative?
- strands from original DNA molecule act as a template
- new DNA molecule contains 1 parent strand and one new stand
49
Outline the process of semi-conservative DNA replication
- DNA helicase breaks H-bonds between base pairs
- Each strand acts as a template
- Free nucleotides form nuclear sap attach to exposed bases by complementary base pairing
- DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strands.
- DNA polymerase build the new strand in one direction (5’ to 3’ direction)
- DNA ligase joins Okizaki fragments on lagging strand by catalysing the formation of phosphodiester bonds.
- H-bonds reform
50
Use your knowledge of enzyme action to suggest why DNA polymerase moves in opposite directions along DNA strands.
- DNA has antiparallel strands
- so 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)
51
Describe the Meselson-Stahl experiment
- bacteria were grown in a medium containing heavy isotope N15 for many generation
- some bacteria were moved to a medium containing light isotope 14N. Samples were extracted after 1&2 cycle of DNA replication
- centrifugation formed a pellet. Heavier DNA( bases made from 15N) settled closer to bottom of tube.
- lighter DNA bases would settle towards the top of the tube
52
Explain how the Meselson-Stahl experiment validated semi-conservative replication.
- Because all the DNA molecules settled in the middle of the tube. meaning they contained both the heavy 15N and light 14N nitrogen and settled in the middle of the tube.
- As one strand of each DNA molecule would be from the original DNA containing the heavier nitrogen and the other (new) strand would be made using only the lighter nitrogen).
53
Why is water a polar molecule?
- unevenl distribution of electrons between H and O.
- forms A slightly negative oxygen and a slightly positive hydrogen
54
Explain five properties that make water important for organisms. (5)
- A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
- A solvent so (metabolic) reactions can occur
- High specific heat capacity so buffers changes in temperature;
- Large latent heat of vaporisation so provides a cooling effect (through evaporation);
- Cohesion (between water molecules) so supports columns of water (transpiration stream in plants
- Cohesion (between water molecules) so produces surface tension
supporting (small) organisms
55
What are inorganic ions and where are they found in the body?
- ions that do not contain carbon atoms
- they are found in the cytoplasm and extracellular fluid
- either in very high or low concentrations
56
State and explain the property of water that helps to prevent temperature
increase in a cell.
- High (specific) heat capacity;
- Buffers changes in temperature;
57
State and explain the property of water that can help to buffer changes in
temperature.
- water has a high specific heat capacity
- can gain energy without changing temperature or takes a lot of heat to change temperature
58
Give two properties of water that are important in the cytoplasm of cells.
For each property of water, explain its importance in the cytoplasm. (4)
1. polar molecule
2. acts as a universal solvent
3. reactive
4. takes place in hydrolysis/
condensation /named reaction
59
What are inorganic ions and where are they found in the body?
- ions that do not contain carbon atoms
- they are found in the cytoplasm and extracellular fluid
- either in very high or low concentrations
60
Explain the role of hydrogen ions in the body.
- high concentration of H+ ions = low acidic pH
- it determines the pH of bodily fluids including blood pH
- H+ ions interact with H-bonDs and ionic bonds in tertiary structure of proteins, which can cause them to denature
61
Explain the role of iron ions in the body.
- Fe2+ bInds to porphyrin ring to form haem group in haemoglobin
- are involved in the transfer of electrons during respiration and photosynthesis, so they are key to the biological generation of energy
- Haemoglobin is made up of four polypeptide chains that each contain one Fe2+
62
Explain the role of sodium ions in the body.
- involved in co-transport for absorption of glucose and amino acids in lumen of gut
- involved in transmission of neurons
63
Explain the role of phosphate ions in the body
- it is a component of DNA , ATP , NADP , cAMP
- involved in ATP synthesis
- responsible for the phosphorylation of molecules which lowers activation energy & speeds up metabolic processes
64
Describe the roles of iron ions, sodium ions, and phosphate ions in cells. (5)
Iron ions:
1. Haemoglobin binds/associates with oxygen
2. involved in the transfer of electrons during respiration and photosynthesis, so they are key to the biological generation of energy
Sodium ions:
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;
Phosphate ions:
6. Affects osmosis/water potential;
Accept 5. OR 6. – not both
- Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
8. used to produce ATP;
9. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;
65
A high concentration of sodium in the blood can affect blood volume and
cause hypertension.
Use your knowledge of water potential to suggest how high sodium
concentrations in the medicines taken could affect blood volume.
1. (Sodium ions) lower the water potential (of blood);
2. Water would move into the blood by osmosis (from cells/tissue fluid);
3. Increasing the blood volume;
66
Explain the role of ATP in cells.
- energy released is coupled to metabolic reactions
- phosphate group phosphorylates compounds to make them more reactive
67
Give the equation for the hydrolysis of ATP. Include named enzyme.
ATP hydrolase catalyses ATP --> ADP + Pi
68
How is ATP resynthesized in cells?
- ATP synthase catalyses condensation reaction between ADP + Pi
- during photosynthesis & respiration
69
ATP is useful in many biological processes. Explain why. (4)
1. Releases energy in small /
manageable amounts.
2. It is broken down in one step
3. It's an immediate energy
compound.
4. Phosphorylates substances and makes them more reactive/ lowers activation energy;
6. It can be reformed/resynthesised.
