[3.1] Biological Molecules Flashcards
Monomers & Polymers, Carbohydrates, Lipids, Proteins & Enzymes, Nucleic Acids, ATP, Water & Inorganic Ions (78 cards)
1
Q
What are monomers & polymers?
A
- Monomers are the smaller units from which larger molecules are made.
- Polymers are molecules made from a large number of monomers joined together.
2
Q
What happens in condensation & hydrolysis reactions?
A
CONDENSATION REACTION
- 2 molecules join together
- Forming a chemical bond
- Releasing a water molecule
HYDROLYSIS REACTION
- 2 molecules separated
- Breaking a chemical bond
- Using a water molecule
3
Q
Give examples of polymers and the monomers from which they’re made.
A
- Polynucleotide (DNA or RNA) - made up of nucleotides.
- Polysaccharide (starch, cellulose, glycogen) - made up of monosaccharides.
- Polypeptide - made up of amino acids.
4
Q
Are lipids polymers?
A
- Lipids are not polymers as they are not made up of repeating monomers.
- Instead lipids are known as macromolecules.
5
Q
What are monosaccharides? Give 3 common examples.
A
- Monosaccharides are the monomers from which larger carbohydrates are made.
- Glucose, galactose and fructose are common monosaccharides.
6
Q
What are disaccharides and how are they formed?
A
- Two monosaccharides joined together with a glycosidic bond
- Formed by a condensation reaction, releasing a water molecule.
7
Q
List 3 disaccharides and the monosaccharides from which they’re made.
A
- Maltose - glucose + glucose
- Sucrose - glucose + fructose
- Lactose - glucose + galactose
8
Q
Draw the structure of an alpha-glucose molecule.
A
9
Q
Draw the structure of a beta-glucose molecule.
A
10
Q
Draw a diagram to show how two molecules of alpha-glucose join together.
A
11
Q
What are polysaccharides and how are they formed?
A
- Many monosaccharides joined together with glycosidic bonds
- Formed by many condensation reactions, releasing water molecules.
12
Q
Describe the basic function and structure of starch.
A
FUNCTION OF STARCH
- Energy store in plant cells.
STRUCTURE OF STARCH
- Polysaccharide formed by the condensation of alpha-glucose molecules.
- Amylose - 1,4-glycosidic bonds, unbranched.
- Amylopectin - 1,4- & 1,6-glycosidic bonds, branched.
13
Q
Describe the basic function and structure of glycogen
A
FUNCTION OF GLYCOGEN
- Energy store in animal cells.
STRUCTURE OF GLYCOGEN
-
Polysaccharide formed by the condensation of alpha-glucose
molecules. - 1,4- & 1,6-glycosidic bonds, branched.
14
Q
Explain how the structures of starch and glycogen relate to their functions.
A
STARCH (AMYLOSE)
- Helical - compact for storage in cell.
- Large, insoluble polysaccharide molecule - can’t leave cell/cross cell membrane.
- Insoluble in water - water potential of cell not affected.
STARCH (AMYLOPECTIN) & GLYCOGEN
- Branched - compact so fits more molecules in small area.
- Branched - more ends for faster hydrolysis to release glucose for respiration to make ATP for the release of energy.
- Large, insoluble polysaccharide molecule - can’t leave cell/cross cell membrane.
- Insoluble in water - water potential of cell not affected.
15
Q
Describe the basic function and structure of cellulose.
A
FUNCTION OF CELLULOSE
- Provides strength and structural support to plant/agal cell walls.
STRUCTURE OF CELLULOSE
- Polysaccharide formed by the condensation of beta-glucose molecules.
- 1,4-glycosidic bond - straight, unbranched chains.
- Chains linked in parallel by hydrogen bonds forming microfibrils.
16
Q
Explain how the structure of cellulose relates to its function.
A
-
Every other beta-glucose molecule is inverted in a long, straight,
unbranched chain. -
Many hydrogen bonds link parallel strands, known as crosslinks, to
form microfibrils. - Hydrogen bonds are strong in high numbers.
- So provides strength to plant cell walls.
17
Q
Name some reducing sugars and describe how to test for them.
A
Reducing sugars = monosaccharides, maltose, lactose.
- Add Benedict’s solution to sample.
- Heat in a boiling water bath.
- Positive result = green/yellow/orange/red precipitate.
(Darker precipitate indicates a higher quantity of sugar)
18
Q
Name a non-reducing sugar and describe how to test for it.
A
Non-reducing sugar = sucrose
- Do Benedict’s test and stays blue indicates a negative result.
- Heat in a boiling water bath with acid (to hydrolyse into reducing sugars).
- Neutralise with an alkali such as sodium hydrogencarbonate.
- Heat in a boiling water bath with Benedict’s solution.
- Positive result = green/yellow/orange/red precipitate.
19
Q
Describe the biochemical test for starch.
A
- Add iodine dissolved in potassium iodide to sample and shake/stir.
- Brown/orange to blue/black indicates positive result.
20
Q
Suggest two methods to measure the quantity of sugar in a solution.
A
METHOD 1
- Carry out a Benedict’s test.
- Filter and dry the precipitate.
- Find the mass/weight.
METHOD 2
- Make sugar solutions of known concentrations - dilution series.
- Heat a set volume of each sample with a set volume of Benedict’s solution for the same time.
- Use colourimeter to measure absorbance of each known concentration.
- Plot calibration curve - concentration x-axis and absorbance on y-axis and draw line of best fit.
- Repeat Benedict’s test with unknown sample and measure absorbance.
- Read off calibration curve to find concentration associated with unknown sample’s absorbance.
21
Q
Name two groups of lipids.
A
Triglycerides and phospholipids.
22
Q
Describe how triglycerides form.
A
- 1 glycerol molecule and 3 fatty acids
- Condensation reaction
- Removing 3 water molecules
- Forming 3 ester bonds
23
Q
Describe the structure of a fatty acid.
A
- Variable R-group - hydrocarbon chain which can be saturated or unsaturated.
- -COOH - carboxyl group
24
Q
Describe the difference between saturated and unsaturated fatty acids.
A
- Saturated: no C=C double bonds in hydrocarbon chain; all fully saturated with hydrogen.
- Unsaturated: one or more C=C double bond in hydrocarbon chain which creates a bend/kink.
25
Describe the difference between the structure of triglycerides & phospholipids.
One of the fatty acids of a triglyceride is substituted by a **phosphate-containing group (PO₄³⁻)**.
26
What is the function of triglycerides?
Explain how the properties of triglycerides are related to their structure.
_FUNCTION_
- Energy storage
_HOW THE PROPERTIES OF TRIGLYCERIDES RELATE TO THEIR STRUCTURE_
- High ratio of **C-H bonds to carbon atoms** in hydrocarbon chain
- So used in **respiration** to release **more energy** than same mass of carbohydrates.
- **Hydrophobic/non-polar** fatty acids so **insoluble** in water
- So no effect on **water potential** of cell.
27
What is the function of phospholipids?
Explain how the properties of phospholipids are related to their structure.
_FUNCTION OF PHOSPHOLIPIDS_
- Form a bilayer in **cell membrane**, allowing diffusion of **lipid-soluble (non-polar)** or very small substances and restricting movement of **water-soluble (polar)** or larger 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 and point towards the interior of the membrane instead.
28
Describe the test for lipids.
1. Add **ethanol, shake** and then add **water**.
2. A milky white **emulsion** indicates a positive test.
29
Draw and describe the general structure of an amino acid.
- **COOH** - represents a carboxyl group.
- **H₂N** - represents an **amine** group
- **R** = variable side chain/group
30
How many amino acids are common in all organisms? How do they vary?
There are **20** amino acids that are common in all organisms and they only vary in their **side group (R)**.
31
Describe how amino acids join together.
- **Condensation** reaction.
- Removing a **water** molecule.
- Between **carboxyl/COOH group** on one amino acid and **amine/NH₂** group of another.
- Forming a **peptide bond**.
32
What are dipeptides and polypeptides?
- **Dipeptide** - formed by the condensation of **two** amino acids.
- **Polypeptides** - formed by the condensation of **many** amino acids.
33
Describe the primary structure of a protein.
**Sequence** of amino acids in a polypeptide chain, joined by peptide bonds.
34
Describe the secondary structure of a protein.
- Folding of polypeptide chain into an **alpha helix** or **beta pleated sheet**
- Due to **hydrogen bonding** between amino acids
- Between **NH** and **C=O**.
35
Describe the tertiary structure of a protein.
- **3D folding** of polypeptide chain
- Due to **interactions** between acid **R groups**
- Forming **hydrogen bonds, ionic bonds** and **disulfide bridges**
36
Describe the quaternary structure of a protein.
- **More than one polypeptide** chain
- Formed by interactions **between polypeptides** (hydrogen bonds, ionic bonds, disulfide bridges).
37
Describe the test for proteins.
1. Add **biuret reagent** (sodium hydroxide + copper (II) sulphate)
2. **Purple/lilac** colour is a positive result as it indicates the presence of
peptide bonds (negative stays blue)
38
How do enzymes act as biological catalysts?
Each enzyme **lowers activation energy** of reaction it catalyses to **speed up** the rate of reaction.
39
Describe the induced-fit model of enzyme action.
1. **Substrate binds** to **active site** of enzyme.
2. Causing active site to **change shape** so it is **complementary** to substrate.
3. So **enzyme-substrate complex** forms.
4. Causing **bonds** in substrate to **bend/distort**, lowering activation energy.
40
Explain the specificity of enzymes.
- **Specific tertiary structure** determines the shape of **active site**
- Dependent on **sequence of amino acids** (primary structure).
- Active site is **complimentary** to specific substrate.
- Only this substrate can bind to active site, **inducing fit** and forming an **enzyme-substrate complex**.
41
Describe how models of enzyme action have changed over time.
- Initially **lock and key** model
- Active site is a **fixed shape, complementary** to one substrate.
- Now **induced-fit** model.
42
Describe and explain the effect of enzyme concentration on the rate of enzyme-controlled reactions.
- As enzyme concentration increases, rate of reaction **increases**
- **Enzyme concentration = limiting factor**
- More enzymes so more available **active sites**
- So more **enzyme-substrate complexes** form
- At a certain point, the rate of reaction **stops increasing and levels off**
- **Substrate concentration** has become a **limiting factor** as all substrates are in use
43
Describe and explain the effect of substrate concentration on the rate of enzyme-controlled reactions.
- As substrate concentration increases, rate of reaction **increases**
- **Substrate concentration = limiting factor**
- More **enzyme-substrate complexes** form
- At a certain point, the rate of reaction **stops increasing and levels off**
- **Enzyme concentration** becomes a **limiting factor**
- As all active sites are **saturated/occupied**
44
Describe and explain the effect of temperature on the rate of enzyme-controlled reactions.
- As temperature increases **up to optimum**, rate of reaction **increases**
- More **kinetic energy**
- So more **enzyme-substrate complexes** form
- As temperature increases **above optimum**, rate of reaction **decreases**
- Enzymes **denature - tertiary** structure and **active site change shape**
- As **hydrogen bonds/ionic bonds break**
- So active site **no longer complementary**
- So fewer **enzyme-substrate complexes** form
44
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
44
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 substrate **can't bind** and fewer **enzyme-substrate complexes** form
- Increasing substrate concentration **reduces effect** of inhibitors.
45
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**
- Changes enzyme **tertiary structure** thus changing the **shape of the active site**
- So active site **no longer complementary** to substrate
- So substrates **can't bind** and fewer **enzyme-substrate complexes** form
- Increasing substrate concentration has **no effect** on the rate of
reaction as change to active site is **permanent**
45
Describe the basic functions of DNA and RNA in all living cells.
- DNA - holds **genetic information** which codes for **polypeptides** (proteins).
- RNA - **transfers** genetic information from **DNA to ribosomes**.
46
Name the two types of molecules from which a ribosome is made.
**RNA** and **proteins**.
47
Draw and label a DNA nucleotide and an RNA nucleotide.
48
Describe the difference between a DNA nucleotide and an RNA nucleotide.
_DNA NUCLEOTIDE_
- Pentose sugar is **deoxyribose**.
- Base can be **thymine**.
_RNA NUCLEOTIDE_
- Pentose sugar is **ribose**.
- Base can be **uracil**.
49
Describe how nucleotides join together to form polynucleotides.
- **Condensation** reactions, removing **water** molecules
- Between **phosphate group** of one nucleotide and **deoxyribose/ribose** of another
- Forming **phosphodiester bonds**
50
Why did many scientists initially doubt that DNA carried the genetic code?
The relative **simplicity** of DNA - chemically simple molecule with few components.
51
Describe the structure of DNA.
- **Polymer** of **nucleotides (polynucleotide)**.
- Each nucleotide formed from **deoxyribose**, a **phosphate group** and a **nitrogen-containing organic base**.
- **Phosphodiester bonds** join adjacent nucleotides.
- **2** polynucleotide chains held together by **hydrogen bonds** between specific **complimentary base pairs** - **adenine/thymine** and **cytosine/guanine**.
- **Double helix**.
52
Describe the structure of (messenger) RNA
- **Polymer** of **nucleotides** (polynucleotides).
- Each nucleotide formed from **ribose**, a **phosphate group** and a **nitrogen-containing organic base**.
- Bases - **uracil**, adenine, cytosine and guanine.
- **Phosphodiester bonds** join adjacent nucleotides.
- **Single helix**.
53
Compare and contrast the structure of DNA and (messenger) RNA
_DNA NUCLEOTIDE_
- Pentose sugar is **deoxyribose**.
- Has the base **thymine**.
- **Double**-stranded/double helix.
- Long (many nucleotides).
- Has **hydrogen bonds/base pairing**.
_RNA NUCLEOTIDE_
- Pentose sugar is **ribose**.
- Has the base **uracil**.
- **Single**-stranded/single helix.
- Shorter (fewer nucleotides).
- **Does not** have hydrogen bonds/base pairing.
54
Suggest how the structure of DNA relates to its functions.
- **Two** strands so both can act as **template** strands for **semi-
conservative replication**.
- **Hydrogen bonds** between bases are weak so strands can be
separated for **replication**.
- **Complementary** base pairing so **accurate** replication.
- **Many** hydrogen bonds between bases so **stable/strong** molecule.
- Double helix with **sugar-phosphate backbone** protects bases/**hydrogen bonds**.
- **Long** molecule so stores **lots** of genetic information that codes for polypeptides.
- **Double helix** so **compact**.
55
Suggest how you can use incomplete information about the frequency of bases on DNA strands to find the frequency of other bases.
1. % of **adenine** in strand 1 = % of **thymine** in strand 2 (vice versa).
2. % of **guanine** in strand 1 = % of **cytosine** in strand 2 (vice versa).
- Because of specific **complementary base pairing** between 2 strands.
56
Why is semi-conservative replication important?
Ensures **genetic continuity** between generations of cells.
57
Describe the 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** 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**.
58
What does semi-conservative mean in terms of DNA?
Each new DNA molecule consists of **one original/template strand** and **one new strand**.
59
Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.
**Watson** and **Crick**.
60
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)** and nitrogen is incorporated into DNA **bases**.
- DNA extracted & centrifuged where it settles near **bottom** as all DNA molecules contain two 'heavy' strands.
2. Bacteria transferred to medium containing **light nitrogen (¹⁴N)** and allowed to divide **once**
- DNA extracted and centrifuged where it settles in **middle** as all DNA molecules contain 1 original 'heavy' strand and 1 new 'light' strand.
3. Bacteria in **light nitrogen (¹⁴N)** allowed to divide **again**.
- DNA extracted and centrifuged where half settles in **middle** as it contains 1 original 'heavy' strand and 1 new 'light' strand.
- The other half settles near **top** as it contains 2 'light strands'.
(Other models **not** supported - bands would be in different places)
61
What is ATP?
**Adenosine triphosphate**.
62
Describe the structure of ATP.
- **Ribose** bound to a molecule of **adenine** and **3 phosphate groups** (PO₄³⁻).
- **Nucleotide derivative**.
63
Describe how ATP is broken down.
1. ATP + (water) -> **ADP** (adenosine diphosphate) + **Pi** (inorganic phosphate)
2. **Hydrolysis** reaction, using a **water** molecule.
3. Catalysed by **ATP hydrolase**.
64
Give two ways in which the hydrolysis of ATP is used in cells.
1. Coupled to **energy-requiring reactions** within cells (releases/provides energy)
- E.g. active transport, protein synthesis.
2. **Inorganic phosphate** released can be used to **phosphorylate** (add phosphate to) other compounds, making them **more reactive**.
65
Describe how ATP is resynthesised in cells.
1. **ADP + Pi** -> ATP (+ water)
2. **Condensation** reaction, removing a **water** molecule.
3. Catalysed by **ATP synthase**.
4. During **respiration** and **photosynthesis**.
66
Suggest how the properties of ATP make it a suitable immediate source of energy for cells.
1. Releases energy in **small** amounts/little energy **lost** as **heat**.
2. **Single** reaction/**one bond** hydrolysed to release energy so immediate release.
3. **Cannot** pass out of cell.
67
Explain how hydrogen bonds occur between water molecules.
1. Water is a **polar** molecule.
2. Slightly negative charged oxygen atoms **attract** slightly positive
charged hydrogen atoms of **other water molecules**.
68
Explain 5 properties of water that are important in biology.
1. **Metabolite**.
- Used in **condensation / hydrolysis /photosynthesis / respiration**.
2. **Solvent** (dissolves solutes).
- Allows **metabolic reactions** to occur (faster in solution).
- Allows **transport** of substances e.g. nitrates in xylem, urea in blood.
3. **High specific heat capacity**
- **Buffers** changes in temperature as water can **gain/lose** a lot of **heat/energy** without changing temperature.
- This makes it a good **habitat** for aquatic organisms as temperature is more **stable** than land.
- Helps organisms maintain a **constant internal body temperature**.
4. **High latent heat of vaporisation**.
- Provides a **cooling** effect with little loss of water through
**evaporation** (e.g. sweat)
- So helps organisms maintain a **constant internal body temperature**.
5. **Strong cohesion between water molecules**.
- Supports **columns** of water (e.g. **transpiration stream**) through xylem in plants.
- Produces **surface tension** where water meets air, supporting small organisms (to walk on water).
69
Where are inorganic ions found in the body?
In solution in **cytoplasm** and **body fluid**, some in high concentrations and others in very low concentrations.
70
Describe the role of hydrogen, iron, sodium and phosphate ions.
_HYDROGEN IONS (H⁺)_
- Maintain **pH** levels in the body.
- High concentration = acidic, low pH.
- Low concentration = alkali, high pH.
- Affects **enzyme** rate of reaction as can cause enzymes to **denature**.
_IRON IONS (Fe²⁺)_
- Component of **haem group** of **haemoglobin**.
- Allowing **oxygen** to **bind/associate** for **transport** as oxyhaemoglobin.
_SODIUM IONS (Na⁺)_
- Involved in **co-transport** of **glucose/amino acids** into cells.
- Involved in **action potentials** in neurons.
- Affects **water potential** of cells/**osmosis**.
_PHOSPHATE IONS (PO₄³⁻)_
- Component of **nucleotides** allowing **phosphodiester bonds** to form in DNA & RNA.
- Component of **ATP**, allowing **energy release**.
- **Phosphorylates** other compounds making them more **reactive**.
- **Hydrophilic** part of **phospholipids**, allowing a **bilayer** to form.
71
Describe the difference between the structure of a-glucose and b-glucose.
- **OH** group is **below carbon 1** in **alpha-glucose** but **above carbon 1** in **beta-glucose**.
(Alpha & beta glucose are **isomers** - same molecule formula, differently arranged atoms)
72
Use your knowledge of enzyme action to suggest why DNA polymerase moves in opposite directions along DNA strands.
1. DNA has **antiparallel** strands.
2. So shapes/arrangements of nucleotide on two ends are **different**.
3. DNA polymerase is an enzyme with a **specific shaped active site**.
4. So can only bind to substrate with **complementary shape**.
73
What equation would you use to calculate pH if you were given the hydrogen ion concentration of a solution?
pH = -log₁₀[H⁺]
74
Draw a diagram to show the formation of a dipeptide.
75
Draw a diagram to show the structure of an ATP molecule.
