3.1 Biological molecules Flashcards
1
Q
3.1.1 Monomers & Polymers
What are monomers?
A
Smaller units from which larger molecules are made. (polymers)
2
Q
3.1.1 Monomers & Polymers
What are polymers?
A
Molecules made from larger number of monomers joined together via a condensation reaction.
3
Q
3.1.1 Monomers & Polymers
Outline some examples of monomers.
A
- Monosaccharides (glucose, fructose, galactose)
- Amino acids
- Nucleotides.
4
Q
3.1.1 Monomers & Polymers
Outline some examples of polymers.
A
- Polysaccharides
- Proteins
- DNA / RNA
5
Q
3.1.1 Monomers & Polymers
What is a condensation reaction?
A
Joins two molecules together with a formation of a **chemical bond **and involves the elimination of a water molecule.
6
Q
3.1.1 Monomers & Polymers
What is a hydrolysis reaction?
A
Breaks a chemical bond between two molecules and involves the addition of a water molecule.
7
Q
3.1.2 Carbohydrates
What are monosaccharides?
A
The monomers from which larger carbohydrates are made.
8
Q
3.1.2 Carbohydrates
Outline some examples of monosaccharides.
A
- Glucose
- Galactose
- Fructose
Formula C6H12O6
9
Q
3.1.2 Carbohydrates
Outline some features of monosaccharides.
A
- Sweet tasting
- Soluble substances
- General formula : (CH2O)n
n can be any number between 1 and 7
10
Q
3.1.2 Carbohydrates
Name the type of bond formed when monosaccharides react.
(Including how diasaccharides and polysaccharides are formed and number of GB.)
A
(1,4 or 1,6) glycosidic bond via a condensation reaction.
2 monomers = 1 chemial (glycosidic) bond = diasaccharide.
many monomers = many chemical (glycosidic) bonds = polysaccharide.
11
Q
3.1.2 Carbohydrates
Name 3 diasaccharides and explain how they are formed.
A
- Maltose: glucose + glucose
- Sucrose: glucose + fructose
- Lactose: glucose + galactose
all have molecular formula C12H22O11
2 monosaccharides form a glycosidic bond via a condensation reaction.
12
Q
3.1.2 Carbohydrates
Glucose has two isomers. What are these two isomers called?
A
A-glucose
B-glucose
13
Q
3.1.2 Carbohydrates
Describe the structure of A-glucose.
A
A H A
(alpha hydrogen above)
-OH bond below
14
Q
3.1.2 Carbohydrates
Describe the structure of B-glucose.
A
BHB
(beta hydrogen below)
OH bond above.
15
Q
3.1.2 Carbohydrates
Outline some features of polysaccharides.
A
1.Very large molecules.
2. insoluble
} makes it good for storage.
16
Q
3.1.2 Carbohydrates
What are 3 examples of polysaccharides?
A
- Starch
- Glycogen
- Cellulose
17
Q
3.1.2 Carbohydrates
Outline the basic structure of starch and its’ role.
A
BASIC STRUCTURE
1. Found in plants.
2. formed from condensation of A-glucose
3. chains may be branched or unbranched.
4. Amylopectin: 1,4 and 1,6 GB.
5. Amylose: 1,4 GB.
ROLE
1. Insoluble ∴ doesn’t affect ψ, so water not drawn into cells by osmosis.
2. large and insoluble } does not diffuse out of cells.
3. Compact, stored in small space.
4. Branched form has many ends } can be acted upon by enzymes simulatenously } glucose monomers released rapidly.
5. When hydrolysed, forms A-glucose, can be transported and readily used in respiration.
18
Q
3.1.2 Carbohydrates
What is the difference between amylopectin and amylose?
A
Amylopectin:
1. 1,4 and 1,6 GB
2. A-Glucose
2. Branched form has many ends } can be acted upon by enzymes simulatenously } glucose monomers released rapidly.
3. Increase in SA
Amylose:
1. 1,4 GB
2. Unbranched helix molecule
3. compact so can fit lots of glucose in small space.
19
Q
3.1.2 Carbohydrates
Outline the basic structure of glycogen and its’ role.
A
BASIC STRUCTURE
1. found in animals only.
2. formed from condensation of A-glucose
3. 1,4 and 1,6 GB.
4. Has shorter chains and is more branched.
5 . stored in small granules mainly in muscle and liver.
ROLE
1. Insoluble ∴ doesn’t affect ψ, so water not drawn into cells by osmosis.
2. Insoluble } does not diffuse out of cells.
3. Compact } lots of it can be stored in small space.
4. More branched than starch } has more ends that can be acted upon simultaneously by enzymes } more rapidly broken down to form glucose monomers used in respiration } important as animals have a higher metabolic rate than plants as they are more active.
20
Q
3.1.2 Carbohydrates
Outline the basic structure of cellulose and its’ role.
A
Basic structure
1. Plants only
2. formed from condensation of B-glucose
3. 1,4 GB.
4. straight chain & unbranched molecule.
5. Chains run paralell to each other } allows H bonds to form cross linkages between adjacent chains.
6. Has adjacent glucose molecules that can rotate 180
7. Celluose molecules are grouped together to form microfibrils.
ROLE
1. Many H bonds provide collective strength.
2. Provides ridgity to plant cell.
3. Cellulose cell wall prevents cell from bursting as water enters it by osmosis.
4. B-glucose } forms long, straight unbranched chains
5. Cellulose molecules grouped together to form microfibrils which are grouped again to form fibres providing more strength.
21
Q
3.1.2 Carbohydrates
Desribe the steps for the biochemical test for reducing sugars.
A
- Add 2cm3 of food sample to a test tube. If sample is not in a liquid form first grind it up.
- Add equal volume of Benedict’s reagent.
- Heat mixture in gently boiling water bath for 5 minuites.
- If reducing sugar present solution turns from blue to orange / brown.
22
Q
3.1.2 Carbohydrates
What is a reducing sugar?
A
Sugar that can donate electrons to reduce another chemical in this case Benedict’s reagent.
23
Q
3.1.2 Carbohydrates
Describe the steps for the biochemical test for non-reducing sugars.
A
- (Using a new sample) if sample is not in liquid form, grind it up.
- Add 2cm3 of the food sample and add 2cm3 of HCL in a test tube and place in a gently boiling water bath for 5 minuites. Dilute HCL will hydrolyse any diasaccharides into its’ consitutent monosaccharides.
- Slowly add NAHCO3 to test tube in order to neutralise HCL.
- Re-test solution by adding 2cm3 of benedict’s reagent into gently boiling water bath for 5 minuites.
- Blue to orange / brown (if non-reducing sugar was present in the original sample)
24
Q
3.1.3 Lipids
Describe the characteristics of lipids.
A
Contain C,H,O
proportions of O: C and H is smaller than in carbohydrates
insoluble in water
Soluble in organic solvents such as alchohol and acetone.
25
# ***3.1.3 Lipids***
What are the roles of lipids?
1. **Source of energy** : When [O] lipids provide >X2 the energy as the same mass of carbohydrate and release valuble water.
2. **Waterproofing** : Lipids are insoluble in H2O
3. **Insulation** : Fats = slow conductors of heat, stored beneath body surface to retain body heat. Act as electrical insulators in myelin sheath around nerve cells.
4. **Protection** : Fats stored around delicate organs such as kidneys.
26
# ***3.1.3 Lipids***
What are the **two main** groups of lipids called?
1. Triglycerides
2. Phospholipids
27
# ***3.1.3 Lipids***
How are triglycerides formed?
By the condensation of **one molecule of a glycerol** and **three molecules of fatty acid** forming an **ester bond.**
28
# ***3.1.3 Lipids***
What is the general formula of a fatty acid?
RCOOH
| R group may be saturated or unsaturated.
29
# ***3.1.3 Lipids***
What is a **saturated** fatty acid?
Contains **no double bond.** (Carbons are linked to max n.o of hydrogen atoms. i.e. saturated with hydrogens.)
**Straight chain** molecules } have many contact points.
Higher mp } solid at room temp
Found in **animal fats.**
30
# ***3.1.3 Lipids***
What is an **unsaturated** fatty acid?
**Contains double bond.**
**Mono-unsaturated** } single double bond between carbon- carbon bond.
**Poly-unsaturated** } +1 double bond between carbon-carbon bonds.
"Kinked" molecules } fewer contact points.
**Lower mp** } liquid at room temp.
Found in **plant oils.**
31
# ***3.1.3 Lipids***
Describe the relation between triglyceride's structure and their properties.
1. **High ratio of energy storing C-H bonds : C atoms** } good source of energy.
2. **Low mass : energy** } good storage molecules as much energy can be stored in small vol. Beneficial to animals as it reduces mass they have to carry when they move around.
3. **Large & non-polar** } insoluble in water } their storage does not affect osmosis in cells or ψ of cells.
4. **Have high H:O** } release water when [O] } provide important source of H2O especially for organisms living in dry deserts.
32
# ***3.1.3 Lipids***
Outline the structure of a phospholipid.
**Glycerol, 2 fatty acids (hydrophobic) and 1 phosphate head (hydrophillic).**
33
# ***3.1.3 Lipids***
What is a phospholipid made up of?
**Hydrophobic tail:** Orients itself away from water but moves readily towards fats.
**Hydrophillic (polar) head:** Interacts with water but not fat.
34
# ***3.1.3 Lipids***
Describe the relation between phosphlipids structure and their properties.
1. **Polar molecules** } has a hydrophillic phosphate head and hydrophobic tail of two fatty acids } forms a bilayer within CSM } hydrophobic barrier formed between in and out of cell.
2. **Hydrophillic phosphate heads** } help to hold at the surface of CSM.
3. **Phospholipid structure** } allows them to form glycolipids by combining with carbohydrates within CSM. } important in cell recognition.
35
# ***3.1.3 Lipids***
Compare phospholipids and triglycerides.
1. Both have glycerol backbone.
2. Both may be attached to a mixture of saturated, mono-unsaturated and polyunsaturated fatty acids.
3. Both contain element C,H,O
4. Both formed via condensation reactions.
36
# ***3.1.3 Lipids***
Contrast phosphlipids and triglycerides.
**Phospholipids:**
2 fatty acids and 1 phosphate group attached.
Hydrophillic head and hydrophobic tail.
Used mainly in membrane formation.
**Triglycerides:**
3 fatty acids attached.
Entire molecule hydrophobic.
Used mainly as a storage molecule } [O] releases energy.
37
# ***3.1.3 Lipids***
Are phospholipids and triglycerides polymers?
**No**, they are not made from small repeating units. They are
**macromolecules.**
38
# ***3.1.3 Lipids***
Describe how to test for lipids in a sample.
1. Add 2cm3 of sample being tested into a test tube (that's dry and grease free) and add 5cm3 of **ethanol**.
2. **Shake** the tube thoroughly to dissolve lipids in sample.
3. **Then** add 5cm3 of **water** and shake gently.
4. A **milky white emulsion** } positive for lipid prescence.
## Footnote
As control, repeat procedures using water instead of sample, the final solution should remain clear.
39
# ***3.1.4 Proteins***
What is an amino acid?
* monomers from which proteins are made from.
40
# ***3.1.4 Proteins***
What is the **general structure** of an amino acid?
R
H2N - C - COOH
H
* NH2 = amine group
* COOH = carboxyl group
* R = side chain
41
# ***3.1.4 Proteins***
How many amino acid groups are common in all organisms and what do they only differ in?
* **20** amino acid groups
* differ in their **side group**
42
# ***3.1.4 Proteins***
What is a dipeptide?
* formed by the condensation reaction between **two amino acid groups**
43
# ***3.1.4 Proteins***
What is a polypeptide?
* formed by the condensation reaction of **many amino acids.**
44
# ***3.1.4 Proteins***
How is a peptide bond formed?
* condensation reaction between two amino acids
45
# ***3.1.4 Proteins***
Functional protein?
* may contain one or more polypeptides.
46
# ***3.1.4 Proteins***
What is the role of **hydrogen bonds** in the protein structure?
**Secondary structure**
* hydrogen bonds form between amino acids in polypeptide chain.
* Makes chain **coiled** (a helix)
* Makes chain **folded** (B pleated sheets)
* There are many but are **easily broken**
47
# ***3.1.4 Proteins***
What is the role of **ionic** bonds in the protein structure?
**Tertiary structure**
* **more bonds form** between different parts of the polypeptide chain, including hydrogen and ionic bonds **further coiling** or **folding** the chain.
* formed between any **carboxyl and amino groups** that are not involved in forming peptide bonds.
* **weaker** than disulfide bridges.
* easily broken by **changes in pH**
48
# ***3.1.4 Proteins***
What is the role of **disulfide bridges** in the protein structure?
* form whenever **2 molecules of amino acid cystenine** come close together.
* Sulfur atom in one cystenine binds to the sulfur atom in the other.
* Fairly strong and **are not** easily broken.
49
# ***3.1.4 Proteins***
Can you describe the relationship between the primary, secondary, tertiary and quaternary structure and protein function?
**PRIMARY:**
* sequence of amino acids in its polypeptide chains.
* **function:** sequence determines its properties and shapes.
**SECONDARY:**
* Shape the polypeptide chain forms is due to hydrogen bonding.
* forms alpha helix or beta pleated sheets.
**TERTIARY:**
* Compact: due to **bending** and **twisting** of the polypeptide helix
* All 3 bonds (H, I, DB) contribute to maintenance of tetiary structure.
**QUATERNARY:**
* Arises from the combination of many different polypeptides chains and associated non-protein groups (**prosthetic**) into **large, complex protein molecule** e.g: haemoglobin.
50
# ***3.1.4 Proteins***
Biuret test for proteins:
1. Add equal volume of **NaOH** to sample at room temp.
2. Add drops of **dilute copper (II) sulfate solution.** Swirl to mix. (steps 1 & 2 make biuret reagent)
3. **Positive result** = colour change from blue to purple.
**Negative result** = solution remains blue.
51
# ***3.1.4 Proteins***
Describe the structure and function of **globular** proteins.
* spherical & compact.
* **Hydrophillic R** group faces outwards.
* **Hydrophobic R** group faces inwards = usually water-soluble.
* involved in **metabolic processes** e.g: enzymes and haemoglobin.
52
# ***3.1.4 Proteins***
Describe the structure and function of **fibrous** proteins.
* can form **long chains** or **fibres**
* insoluble in water.
* useful for structure and support e.g: collagen in skin.
53
# ***3.1.4 Proteins***
Outline how chromatography can be used to identify amino acids in the mixture.
1. Use capillary tube to spot mixture onto **pencil orgin** line and place chromatography paper in solvent
2. Allow solvent to run until it almost touches the other end of paper. Amino acids move different distances based on the **relative attraction** to paper and solubility in solvents.
3. Use UV or revealing agent to see spots.
4. Calculate Rf value and match to database.
54
# ***3.1.4 Proteins***
What are enzymes?
* Biological catalysts for intra and extracellular reactions.
* **Specific** tetiary structure determines shape of the **active site** complementary to a **specific substrate**
* Formation of **E-S complexes** lowers the **Ea** of metabolic reactions.
55
# ***3.1.4 Proteins***
Explain the **induced fit** model of enzyme action.
* Shape of active site is **not complementary** to substrate and is **flexible**
* conformational change **enables** ES complexes to form.
* Puts a **strain** on substrate bonds, lowering Ea.
56
# ***3.1.4 Proteins***
Explain the lock and key model.
* Enzymes are **complementary** to the shape of the **substrate**
* Subsrate will fit into the active site and an **E-S** complex will form.
* Enzyme will **catalyse** the reaction and products will form **E-S** complexes.
57
# ***3.1.4 Proteins***
Specificity of enzymes:
* is due to the tetiary structure of its active site, allowing complementary binding to substrates.
* Enzymes catalyse **intra and extracellular reactions** that determine structure and functions from cellular to whole organism.
58
# ***3.1.4 Proteins***
Name 5 factors that affect the rate of enzyme controlled reactions.
1. Enzyme concentration
2. Susbtrate concentration
3. Concentration of inhibitors
4. pH
5. Temperature
59
# ***3.1.4 Proteins***
How does **enzyme concentration** affect rate of reaction?
* As concentration of enzyme is **increased**, enzyme activity also **increases**.
* More substrate will be broken down if more enzyme is added.
* Once all the substrate have been broken down, the enzyme will no longer have anything to break down therefore the increase in enzyme activity does not occur forever.
60
# ***3.1.4 Proteins***
How does **substrate concentration** affect rate of reaction?
* Once all enzymes have bound, any **susbtrate increase** will have **no effect** on rate of reaction.
* Available enzymes will be **saturated** and working at their **maximum rate.**
61
# ***3.1.4 Proteins***
How does **concentration of inhibitors** affect rate of reaction?
**COMPETITIVE:**
* binds to the active site and prevents subtrate from binding there
**NON-COMPETITVE:**
* binds to a different site on the enzyme
* doesn't block substrate binding
* **BUT** causes other changes in the enzyme so that it can **no longer** catalyse the reaction efficiently.
62
# ***3.1.4 Proteins***
How does **pH** affect the rate of reaction?
* Each enzyme has an **optimum** enzyme pH range.
* **Changing the pH** outside of this range will result in **slow enzyme activity**
* Extreme pH values will cause enzymes to **denature**
63
# ***3.1.4 Proteins***
How does **temperature** affect the rate of reaction?
* **Increasing temp**, speeds up rate of reaction.
* Above optimum temperatures will cause **hydrogen and ionic bonds in the tertiary structure** to break = active site is **no longer complementary** to substrate = **denaturation**
64
# ***3.1.4 Proteins***
**Contrast** competitive and non-competitive inhibitors.
**COMPETITIVE**
* similar shape to substrate = bind to AS
* do not stop reaction = ES complex formed when inhibitor is released.
* Increasing substrate concentration = decreases their effect.
**NON-COMPETITIVE**
* bind at a different site on the enzyme but the active site.
* may permanently stop the reaction = triggers AS to change shape.
* Increasing substrate concentration = has no impact on their no effect
65
# ***3.1.4 Proteins***
State the formula for pH.
pH = -log₁₀ [H⁺]
66
# ***3.1.4 Proteins***
Outline how to calculate rate of reaction from a graph.
* calculate gradient of line
* intial rate = draw tangent at t = 0
67
# ***3.1.4 Proteins***
Outline how to calculate rate of reaction from raw data.
* change in concentration of product or reactant / time
68
# ***3.1.4 Proteins***
Why is advantageous to calculate inital rate?
* represent **maximum** rate of reaction **before concentration of reactants decreases** and "end product inhibition".
69
# ***3.1.4 Proteins***
RP 01 Rate of an Enzyme Controlled Reaction:
1. Make 2 control samples:
* take 2 flat bottom tubes
* Add 5cm3 of **milk suspension** to each tube.
* Add 5cm3 of **distilled water** to one tube = will indicate **abscence of enzyme activity**
* Add 5cm3 of **HCl** to the other = indicates colour of **completely hydrolysed sample**
2. Take 3 test tubes and measure 5cm3 of **milk** into each. Place in the **water bath** at 10°C for 5 mins to equilibriate.
3. Add 5cm3 of **trypsin** to each test tube and start the timer.
4. Record how long it takes for the **milk** sample to **completely hydrolyse** and become **colourless**
5. Repeat **step 2 & 3** at temperatures of 20°C, 30°C, 40°C and 50°C.
6. Find **mean** time for the milk to be hydrolysed at each temp and find out rate of reaction.
7. Rate of reaction = 1 / mean time.
70
# ***3.1.4 Proteins***
What is the conclusion of RP 01 Rate of an Enzyme Controlled Reaction?
* Milk contains protein called **casein**, which when broken down causes milk to become **colourless**
Trypsin is **protease enzyme** which hydrolyses the **casein protein**
* Temp increases from 10°C, kinetic energy increases = more E-S complexes form = rate of reaction increases up to optimum temperature.
* above optimum temperature = **bonds** in **tertiary** structure break, which changes the shape of **active site** = enzyme and substrate are **no longer complementary.**
71
# ***3.1.5 Nucleic acids are important information-carrying molecules***
What is the importance of DNA and RNA?
* important **information-caryying** molecules.
* In all living cells, DNA **holds genetic info** and RNA **transfers genetic info** from DNA to ribosomes.
* Both are polymers of nucleotides.
72
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Describe the structure of a nucleotide.
* Phosphate group
* Pentose sugar
* Nitrogenous base.
73
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Name the pentose sugars in DNA and RNA.
DNA: deoxyribose
RNA: ribose.
74
# ***3.1.5 Nucleic acids are important information-carrying molecules***
How are ribosomes formed?
* RNA and proteins
75
# ***3.1.5 Nucleic acids are important information-carrying molecules***
State the role of DNA in living cells.
* **Base sequence of genetic code** for functional RNA and amino acid sequence of polypeptides.
* Genetic information **determines inherited characteristics** = influences structure and function of organism.
76
# ***3.1.5 Nucleic acids are important information-carrying molecules***
State the role of RNA in living cells.
| including mRNA, rRNA, and tRNA.
* **mRNA:** complementary sequence of **1 gene** from DNA with **introns** (non-coding regions) which are **spliced out**. Codons translated into polypeptide by ribosomes.
* **rRNA:** component of ribosomes (with proteins).
* **tRNA:** supplies **complementary amino acid** to mRNA codons during **translation.**
77
# ***3.1.5 Nucleic acids are important information-carrying molecules***
How do polynucleotides form?
* **Condensation reaction** between two nucleotide forming **phosphodiester bond.**
78
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Describe the structure of DNA.
* **double helix** of two polynucleotide strands (deoxyribose) held together by hydrogen bonds between specific complementary base pairs.
* (A - T)
* (C - G)
| **A**pples grow on **T**rees. **C**ars are parked in **G**arages.
79
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Name the components of a DNA nucleotide.
* Deoxyribose
* A phosphate group
* One of the organic bases adenine, cytosine, guanine or thymine.
80
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Name the components of an RNA nucleotide.
* Ribose
* A phosphate group
* One of the organic bases adenine, cytosine, guanine or **uracil**
81
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Which bases are purine and which are pyrimidine?
A , G = **2-ring purine** bases
T , C , U = **1-ring pyrimidine** bases
82
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Name the complementary bases in DNA.
* A + T = 2 H bonds.
* G + C = 3 H bonds.
83
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Name the complementary bases in RNA.
* A + U = 2 H bonds
* G + C = 3 H bonds
84
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Relate the structure of DNA to its function.
* **sugar phosphate backbone and many H bonds** = provides stability.
* **long molecule** = stores lots of information
* **helix is compact** = good storage in nucleus.
* base sequence of **triplets** codes for amino acids.
* **double stranded** = for semi-conservative replication.
* **complementary base pairing** = accurate replication.
* **weak H bonds break** = strands seperate for replication.
85
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Describe the structure of mRNA (messenger RNA) relative to its function.
* **Long ribose polynucleotide (shorter than DNA)** = breaks down quickly so no excess polypeptide forms.
* Contains **uracil** instead of thymine.
* **Single-stranded + linear (no complementary base pairing)** = ribosomes can move along strand, tRNA can bind to exposed bases
* **Codon sequence complementary to exons of 1 gene from 1 DNA strand** = can be translated into specific polypeptide by ribosomes.
86
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Describe the structure of tRNA (transfer).
* Single strand of about 80 nucelotides.
* folded into a clover shape (H bonds between some complementary bases)
* Anticodon on one end , amino acid binding site on the other.
* Anticodon binds to the complementary mRNA codon.
* Amino acid corresponds to anticodon.
87
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Order DNA, mRNA, and tRNA according to increasing length.
* tRNA
* mRNA
* DNA
88
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Describe the structure of RNA molecule.
* relatively short polynucelotide.
89
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Why did scientists doubt that DNA carried genetic code?
* DNA is a chemically simple molecule with few components = only has four bases so how could it code for 20 amino acids? They reasoned that identical molecules could not carry different instructions across all organisms.
90
# ***3.1.5 Nucleic acids are important information-carrying molecules***
What method is used to replicate DNA?
* semi-conservative replication
91
# ***3.1.5 Nucleic acids are important information-carrying molecules***
What does semi-conservative replication of DNA ensure?
* Genetic continuity between generations of cells.
92
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Why is DNA replication described as semi-conservative?
* Strands from orginigal DNA molecule act as a template strand.
* New DNA molecule contains 1 old strand and 1 new strand.
93
# ***3.1.5 Nucleic acids are important information-carrying molecules***
Outline the process of semi-conservative replication of DNA.
1. **DNA helicase** unwindes the double helix and breaks the hydrogen bonds between the complementary base pairs in the polynucelotide strands.
2. Free nucleotides attach to the exposed bases by complementary base pairing on the template strand.
3. **DNA polymerase** catalyses condensation reactions that join adjacent nucleotides on new strand.
4. H bonds reform and each new DNA molecule contains one strand of the orignal and one strand of the new DNA.
94
# ***3.1.6 ATP***
Describe the structure of ATP.
* Nucleotide derivative.
* formed from a molecule of **ribose** (pentose sugar), a molecule of **adenine** (base) and **three phosphate groups.**
95
# ***3.1.6 ATP***
Explain the role of ATP in cells.
* **ATP HYDROLASE** catalyses ATP -> ADP + Pi.
* energy released is coupled to **metabolic reactions**
* phosphate groups **phosphorylate** compounds to make them **more reactive.**
96
# ***3.1.6 ATP***
How is ATP resynthesised in cells?
* **ATP SYNTHASE** catalyses condensation reaction of ADP + Pi -> ATP during photosynthesis or during respiration.
97
# ***3.1.6 ATP***
Explain why ATP is suitable as the main energy source in cells.
* High energy bonds between phosphate groups.
* Small amount of energy is released at a time = less energy wasted as heat.
* Single-step hydrolysis = energy is available quickly.
* Readily resythesised.
98
# ***3.1.7 Water***
What percentage of cells is made up of water?
* 65%.
99
# ***3.1.7 Water***
Water as a metabolite:
* in many metabolic reactions such as **condensation and hydroylsis reactions** which are used in forming and breaking of chemical bonds.
100
# ***3.1.7 Water***
Water as a solvent:
* readily dissolves other substances (O2 and CO2), wastes (ammonia and urea), inorganic ions and small hydrohillic molecules (amino acids, monosaccharides etc) and enzymes whose reaction takes place in solution.
101
# ***3.1.7 Water***
Water having a high specific heat capacity:
* water molecules stick together via hydrogen bonds = lots of energy required to break these bonds.
* Acts as a buffer = minimising temperature fluctuations.
102
# ***3.1.7 Water***
Water having a large latent heat of vapourisation:
* Hydrogen bonding makes evapouration more difficult to break
* Allows organisms to control their body temperatures i.e. providing a cooling effect with little water loss - sweating.
103
# ***3.1.7 Water***
Water having strong cohesion between molecules:
* enables effective transport of water in tube like the xylem.
* supports columns of water in the tube-like transport cells of plants
* Produces surface tension = when the molecules meet air they tend to pull back into the body of water than escape,
acting like a skin that is strong enough to support small organisms
104
# ***3.1.7 Water***
What is water?
* major component of cells.
* made up from slightly delta + H atoms and a slightly delta - O atom.
105
# ***3.1.8 Inorganic ions***
Where do inorganic ions occur?
* In the solution of the cytoplasm and body fluids of organisms some that are high in concentrations and other that is very low.
106
# ***3.1.8 Inorganic ions***
Outline some essential ions.
* Hydrogen ions
* Iron ions
* Sodium ions
* Phosphate ions
107
# ***3.1.8 Inorganic ions***
Outline the location and function of hydrogen ions.
1. Solutions
2. Determines the pH of substances such as blood and functioning of enzymes.
The higher the concentration of hydrogen ions, lower concentration of pH.
108
# ***3.1.8 Inorganic ions***
Outline the location and function of iron ions.
1. Component of haemoglobin
2. Oxygen carrying molecule in red blood cells.
109
# ***3.1.8 Inorganic ions***
Outline the location and function of sodium ions.
1. Cells
2. Co-transport of glucose and amino acids across membranes.
110
# ***3.1.8 Inorganic ions***
Outline the location and function of phosphate ions.
* component of DNA and ATP.
* structural and store of energy.
