Biological Molecules Flashcards
1
Q
A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.
A
- Compact
- occupies small space
- tightly packed;
2
Q
The structure of cellulose is related to its role in plant cell walls. Explain how. (3)
A
- Long, straight, unbranched chains of Beta glucose;
- (Joined by) many WEAK hydrogen bonds;
- Form microfibrils / macrofibrils;
- Provide rigidity/strength/support;
Reject reference to strong
3
Q
Compare and contrast the structure of starch and the structure of cellulose. [6 marks]
A
- Both polysaccharides OR Both are glucose polymers OR Both are made of glucose monomers;
- Both contain glycosidic bonds (between monomers);
- Both contain carbon, hydrogen and oxygen/C, H and O;
- Starch has α-glucose and cellulose has β-glucose;
- Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
- Starch (molecule) is branched and cellulose is not/unbranched;
7.Cellulose has (micro/macro) fibrils and starch does not; - Starch has 1–6 glycosidic bonds and cellulose does not
OR Starch contains two types of molecule and cellulose contains one type of molecule
OR Starch is amylose and amylopectin and cellulose is one type of molecule;
4
Q
Give one feature of starch and explain how this feature enables it to act as a storage substance.
A
- Helical / spiral So compact / tightly packed / can fit (lots) into a small space;
- Insoluble So no osmotic effect / does not leave cell / does not affect water potential;
- Large molecule / long chain So does not leave cell / contains large number of glucose units;
- Branched chains So rapid hydrolysis to remove glucose for respiration;
5
Q
Hydrogen bonds are important in cellulose molecules. Explain why.
A
- Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils;
- Providing strength/rigidity (to cellulose/cell wall);
- Weak Hydrogen bonds provide strength in large numbers;
6
Q
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.
A
- Glucose and galactose
- Joined by condensation
- Joined by glycosidic bond
- Added to polypeptide in Golgi
7
Q
Describe how the student would show that reducing sugars were present in a solution. [3]
A
- Add Benedict’s;
- Heat to 95°C;
- Red/orange/yellow/green precipitate (shows reducing sugar present);
8
Q
Describe how you would test a sample of food for the presence of starch. [2]
A
- Add potassium iodide (KI) solution to the food sample;
- Blue/black/purple indicates starch is present;
9
Q
Describe how you would test a liquid sample for the presence of a lipid and how you would recognise a positive result. [2]
A
- (Mix / shake sample) with ethanol, then water and shake;
- Cloudy White / milky (emulsion);
10
Q
Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?
A
- Double bond(s);
- (Bonds) between carbon atoms within the hydrocarbon chain;
11
Q
Describe how an ester bond is formed in a phospholipid molecule. [2]
A
- Condensation (reaction) OR Loss of water;
- Between of glycerol and fatty acid;
12
Q
Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)
A
- Crush/grind;
- With ethanol/ alcohol, to dissolve the lipid;
- Then add water then shake;
- Forms a white emulsion / goes white;
13
Q
Compare and contrast the structure and properties of triglycerides and phospholipids [5]
A
- Both contain ester bonds
- Both contain glycerol
- Fatty acids on both may be saturated or unsaturated
- Both are insoluble in water
- Both contain C, H and O but phospholipids are also contain P
- Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group
- Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region
- Phospholipids form monolayer/micelle/bilayer but triglycerides don’t.
14
Q
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample. [6]
A
Lipid
1. Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water;
2. White/milky emulsion OR emulsion test turns white/milky;
Non-reducing sugar
3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange (precipitate);
Amylase
6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing sugar/absence of starch;
15
Q
A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution. [2]
A
- Filter and dry (the precipitate);
- Find mass/weight;
16
Q
Draw alpha glucose.
A
17
Q
Name the bonds found in Glycogen
A
1-4 AND 1-6 Glycosidic bonds
18
Q
Name the monomers found in Lactose
A
(Alpha) Glucose & Galactose
19
Q
Draw a molecule of glycerol.
A
20
Q
Name the bond found between Glycerol and fatty acids.
A
ESTER
21
Q
Why are lipids not classed as polymers? [3]
A
- Made from Fatty acids and glycerol
- not made from similar of identical repeating monomers
- Polymer are 3 or more (usually thousands) similar or identical monomers
22
Q
Describe how a triglyceride molecule is formed [3]
A
- ONE glycerol molecule and THREE fatty acids
- Condensation reactions AND removal of THREE molecules of water
- Ester bonds are formed.
23
Q
Describe how an ester bond is formed in a phospholipid molecule. [2]
A
- Condensation (reaction) OR Loss of water;
- Between OH of glycerol and OH of carboxyl group of fatty acid;
24
Q
Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane [3]
A
- Glycerol joined to two fatty acid tails. Phosphate group joined to glycerol on opposite side. (joined by condensation reaction with ester bond).;
- Phospholipid has a charged, hydrophilic head (phosphate and glycerol) and non-polar hydrophobic tails (fatty acid chains)
- Arrange to form a phospholipid bilayer; (Hydrophilic head facing out towards water. Hydrophobic fatty acid chains facing in, away from water)
25
Describe how monomers join to form the primary structure of a protein. [3]
* Condensation reaction between amino acids;
* (Forming) peptide bonds;
* Creating (specific) sequence/order of amino acids;
26
Draw the general stucture of an amino acid.
27
Draw and label the general structure of an amino acid.
28
Describe how a peptide bond is formed between two amino acids to form a dipeptide. [2]
* Condensation (reaction) / loss of water;
* Between **amine** / NH2 and **carboxyl** / COOH;
29
Describe how the **structure** of a protein **depends** on the amino acids it contains. [5]
* **Structure** is determined by (relative) **position** of amino acid/R group/interactions;
(Accept for 'interactions', hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions)
* **Primary** structure is **sequence**/order of amino acids;
* **Secondary** structure formed by **hydrogen** bonding (between amino acids);
Accept alpha helix/β-pleated sheet for ‘secondary structure’
* **Tertiary** structure formed by **interactions** **between R groups**;
Accept for 'interactions', hydrogen bonds / disulfide bridges / ionic bonds / hydrophobic-hydrophilic interactions
* Creates active site in enzymes OR Creates complementary/specific shapes in antibodies/carrier proteins/receptor (molecules);
* **Quaternary** structure contains **>1 polypeptide** chain OR Quaternary structure formed by interactions/bonds between polypeptides; Accept prosthetic (group)
30
Describe the structure of proteins. [5]
* **Polymer** of amino acids joined by **peptide** bonds;
* Formed by **condensation** reactions;
* Primary structure is number **AND** order of amino acids;
* Secondary structure is folding of polypeptide chain into Alpha-helix and Beta-pleated sheets due to **hydrogen** bonding;
* Tertiary structure is 3-D folding due to hydrogen bonding **and** ionic bonding **and** disulfide bridges;
* Quaternary structure is **two or more polypeptide** chains **joined** together;
31
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample. [6]
**Lipid**
* Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water;
* White/milky emulsion OR emulsion test turns white/milky;
**Non-reducing sugar**
* Do Benedict’s test and stays blue/negative;
* Boil with acid then neutralise with alkali;
* Heat with Benedict’s and becomes red/orange (precipitate);
**Amylase**
* Add biuret (reagent) and becomes purple/violet/mauve/lilac;
* Add starch, (leave for a time), test for reducing sugar/absence of starch;
32
Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why. [3]
* Lactose has a different **shape**/structure;
* Does not fit/bind to active site of enzyme/sucrase;
OR
* Active site of enzyme/sucrase has a specific shape/structure;
* Does not fit/bind to lactose so no **Enzyme-Substrate Complexes** formed.
33
Describe how an enzyme-substrate complex increases the rate of reaction [2]
* Reduces activation energy
* Due to bending bonds OR Without the enzyme, very few substrates have sufficient energy for the reaction.
34
Describe the induced fit model of enzyme action.(2)
* Active site not complementary (to substrate);
* Active site changes **shape** / is flexible;
* (Change in enzyme allows) substrate to able to fit / Enzyme-Substrate complex to form;
35
Describe the induced-fit model of enzyme action **and** how an enzyme acts as a catalyst.
* Substrate binds to the active site/enzyme OR Enzyme-substrate complex forms;
* Active site changes shape (slightly) so it is complementary to substrate OR Active site changes shape (slightly) so distorting/breaking/forming bonds in the substrate;
* Reduces activation energy;
36
Describe one way that the lock and key model is different from the induced fit model (2)
* Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around
* substrate / (already) fits the substrate / is
* Complementary (before binding);
37
What is the effect of increasing substrate concentration has on the rate of an enzyme controlled reaction (3)
* Rate of enzyme activity increases then plateaus / constant / steady / rate does not change;
* It plateaus as all active sites occupied / enzyme is fully **saturated**;
* (rate of reaction) / maximum number of Enzyme-Substrate complexes per second;
38
Explain the effect of increasing temperature on the rate of an enzyme controlled reaction [3]
* Increase in rate of reaction due to increase in kinetic energy
* More enzyme substrate complxes are formed per second.
* Reaches optimum temperature
* Rate decreases after optimum due to denaturation
* Change in the tertiary structure & active site, therefore substarte no longer bonds to active site/ fewer/no enzyme substrate complexes form.
39
What is the effect of pH on the rate of an enzyme controlled reaction [3]
* pH is changed from the optimum (more acidic or more basic)
* **charge** on the R groups of the amino acids is altered and **ionic bonds (and weak H bonds)** in the **tertiary structure** are broken.
* Active site **changes shape** and the substrate can no longer **bind** (no longer specifically complementary). **Less/No enzyme substrate complexes can be formed**, and the rate of the reaction decreases either side of the optimum. The enzyme is **denatured**.
40
Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein. [4]
* Change in primary structure changes sequence of amino acids;
* Hydrogen bonds and Ionic bonds and Disulphide bonds form in different positions;
* Alters the tertiary structure of the enzyme / alters shape of active site;
* No Enzyme-Substrate complexes can be formed;
41
Explain how a competitive inhibitor works [3]
* Inhibitor is a **similar** shape to substrate;
* Inhibitor enters active site / **competes** with **substrate**;
* Less substrate binds/**fewer enzyme-substrate complexes form per second.**
42
Describe how a non-competitive inhibitor works [3]
* Attaches / **binds** to the enzyme at a site other than the active site (**allosteric** site);
* Changes **shape** of the **active site** OR Changes **tertiary** structure (of enzyme) OR causes **conformational** change to active site;
* (So active site and substrate) **no longer** **complementary** so less/no substrate can fit/bind (‘no longer complementary so less/no enzyme-substrate complexes form’);
43
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/2 strands held by hydrogen bonds;
* (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
44
Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. [3]
* Condensation (reaction)/loss of water;
* (Between) phosphate and deoxyribose;
* (Catalysed by) DNA polymerase;
(5' to 3' direction)
45
Describe how the structure of DNA relates to its function. [5]
* Sugar-phosphate (backbone)/double stranded/helix so provides strength/stability /protects bases/protects hydrogen bonds;
* Long/large molecule so can store lots of information;
* Helix/coiled so compact;
* Base sequence allows information to be stored/ base sequence codes for amino acids/protein;
* Double stranded so replication can occur semi-conservatively/ strands can act as templates;
* Complementary base pairing / A-T and G-C so accurate replication/identical copies can be made;
* (Weak) hydrogen bonds for replication/ unzipping/strand separation;
* Many weak hydrogen bonds so stable/strong molecule;
46
State four structural differences between a DNA molecule and an mRNA molecule [4]
* DNA has deoxyribose, mRNA has ribose;
* DNA has thymine, mRNA has uracil;
* DNA longer, mRNA shorter;
* DNA is double stranded, mRNA is single stranded;
* DNA has hydrogen bonds, mRNA has no hydrogen bonds OR DNA has (complementary) base pairing, mRNA does not;
47
Describe Semi-conservative replication. [5]
* Strands separate / H-bonds break;
* DNA helicase (involved);
* Both strands/each strand act(s) as (a) template(s);
* (Free) nucleotides attach;
* Complementary/specific base pairing due to H bonds forming between bases/ Adenine to Thymine and GC;
* DNA polymerase joins nucleotides (on new strand) forming phoshodiester bonds by condensation;
* Semi-conservative replication / new DNA molecules contain one old strand and one new strand;
48
Describe how the separation of strands occurs. [2]
* DNA Helicase;
* Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases OR Breaks hydrogen bonds between polynucleotide strands;
**Reject Hydrolyses H bonds**
49
Describe the role of DNA polymerase in the semi-conservative replication of DNA. [3]
* Joins (adjacent DNA) nucleotides;
* (Catalyses) condensation (reactions);
* (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
**Reject: forms H bonds**
50
Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA. [3]
* Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip;
* Two strands, so both can act as templates;
* Complementary base pairing allows accurate replication;
51
ATP is an energy source used in many cell processes. Give **two** ways in which ATP is a suitable energy source for cells to use.
* Releases relatively small amount of energy/ little energy is lost as heat;
* Releases energy instantaneously;
* Phosphorylates other compounds, making them more reactive;
* Can be rapidly re-synthesised;
* Is not lost from/ does not leave cells;
52
Describe how an enzyme can be phosphorylated. [2]
* Attachment/association of (inorganic) phosphate (to the enzyme);
* (Released from) hydrolysis of ATP OR (Released from) ATP to ADP + Pi;
53
Draw and label a molecule of ATP.
54
Describe how ATP is resynthesised in cells. [3]
1. From ADP and phosphate;
Reject use of water in the reaction
2. By ATP synthase;
3. During respiration/photosynthesis;
55
Explain five properties that make water important for organisms. [5]
* A **metabolite** in condensation/hydrolysis/ photosynthesis/respiration;
* A **solvent** *so (metabolic) reactions can occur* OR A solvent so allowing transport of substances;
* **High 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 (in plants);*
* **Cohesion** (between water molecules) *so produces surface tension supporting (small) organisms;*
56
State and explain the property of water that helps to prevent temperature increase in a cell. [2]
* High (specific) heat capacity;
SO
* Buffers changes in temperature;
57
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]
* Polar molecule SO Acts as a (universal) solvent;
OR
* (Universal) solvent SO (Metabolic) reactions occur faster in solution;
OR
* Reactive SO Takes place in hydrolysis / condensation / named reaction;
* Polar molecule so acts as (universal) solvent so (metabolic reactions are faster = 3 marks
58
Describe the roles of iron ions, sodium ions, and phosphate ions in cells. [5]
**Iron ions**
* Haemoglobin binds/associates with oxygen OR Haemoglobin transports/loads oxygen;
** Sodium ions**
* Co-transport of glucose/amino acids (into cells);
* (Because) sodium moved out by active transport/Na – K pump;
* Creates a sodium concentration/diffusion gradient;
* Affects osmosis/water potential;
**Phosphate ions**
* Affects osmosis/water potential;
* Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
* Used in/to produce ATP;
* Phosphorylates other compounds (usually) making them more reactive;
* Hydrophilic/water soluble part of phospholipid bilayer/membrane
59
Describe the roles of iron ions, sodium ions, and phosphate ions in cells. [5]
**Iron ions**
* Haemoglobin binds/associates with oxygen OR Haemoglobin transports/loads oxygen;
** Sodium ions**
* Co-transport of glucose/amino acids (into cells);
* (Because) sodium moved out by active transport/Na – K pump;
* Creates a sodium concentration/diffusion gradient;
* Affects osmosis/water potential;
**Phosphate ions**
* Affects osmosis/water potential;
* Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
* Used in/to produce ATP;
* Phosphorylates other compounds (usually) making them more reactive;
* Hydrophilic/water soluble part of phospholipid bilayer/membrane
60
Explain why phospholipids can form a bilayer but triglycerides cannot. [3]
1. Phospholipid **both hydrophobic and hydrophilic**
OR Phospholipid **polar** OR Phosphate group is charged;
2. Triglycerides **only hydrophobic** OR
Fatty acid/triglyceride is** non-polar;**
3. Hydrophilic/**phosphate group attracts water** (to
either side of bilayer);
