Biological Molecules Flashcards
1
Q
Define monomer. Give some examples
A
- Smaller units that join together to form larger molecules.
- E.g. monosaccharides, amino acids, nucleotides.
2
Q
Define polymer. Give some examples
A
- Molecules formed when many monomers join together.
- E.g. polysaccharides, proteins, DNA/RNA
3
Q
What happens in a condensation reaction?
A
A chemical bond forms between 2 molecules & a molecule of water is produced.
4
Q
What happens in 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 2 disaccharides. Describe how they form.
A
- Maltose: glucose + glucose
- Sucrose: glucose + fructose
- Lactose: glucose + galactose
7
Q
Describe the structure and functions of starch.
A
- Storage polymer of alpha-glucose in plant cells.
- Insoluble = no osmotic effect
- large = does not diffuse out of cells
8
Q
Describe the structure and functions of glycogen
A
- Main storage polymer of alpha-glucose in animals
- Branched = many terminal ends for hydrolysis
- Insoluble = no osmotic effect and does not diffuse out of cells
- Compact
9
Q
Describe the structure and function of cellulose
A
- Straight-chain, unbranched molecule
- H-bond crosslinks between parallel strands form microfibrils = high tensile strength.
10
Q
Describe the benedict’s test for reducing sugars
A
- Add and equal volume of Benedict’s reagent to a sample.
- Heat the mixture in an electric water bath at 100 degrees for 5 mins.
- Positive result: colour change from blue to orange & brick-red precipitate forms.
11
Q
Describe the Benedict’s test for non-reducing sugars
A
- Negative result: Benedict’s reagent remains blue
- Hydrolyse non-reducing sugars by adding 1cm-cubed of HCl. Heat in a boiling water bath for 5 mins.
- Neutralise the mixture using sodium carbonate solution.
- Proceed with Benedict’s test as usual.
12
Q
Describe the test for starch
A
- Add iodine solution
- Positive result: colour change from orange to blue-black
13
Q
Describe how to test for lipids in a sample
A
- Dissolve solid samples in ethanol
- Add an equal volume of water and shake.
- Positive result: milky white emulsion forms
14
Q
How do triglycerides form?
A
Condensation reaction between 1 molecule of glycerol & 3 fatty acids forms ester bonds.
15
Q
Relate the structure of triglycerides to their functions
A
- High energy: mass ratio = high calorific value from oxidation.
- Insoluble hydrocarbon chain = no effect on water potential
16
Q
Compare phospholipids and triglycerides
A
- Both have glycerol backbone
- Both may be attached to fatty acids
- Both contain the elements, C,H,O
- Both formed by condensation reactions.
17
Q
Are phospholipids and triglycerides polymers?
A
No. They are macromolecules.
18
Q
Are phospholipids and triglycerides polymers?
A
No. They are macromolecules.
19
Q
Why is water a polar molecule?
A
O is more electronegative than H, so attract the pair of electrons in the covalent bond more easily.
20
Q
State 4 important properties of water
A
- Metabloite/solvent for chemical reactions in the body
- High specific heat capacity
- High latent heat of vapourisation
- Cohesion between molecules
21
Q
Explain why water is significant to living organisms
A
- Solvent for polar molecules during metabolic reactions.
- Enables organisms to avoid fluctuations in core temperature.
- Cohesion-tension of water molecules in transpiration stream.
22
Q
What are inorganic ions and where are they found in the body?
A
- Ions that do not contain carbon atoms
- Found in cytoplasm & extracellular fluid
- May be in high or very low concentrations
23
Q
Explain the role of hydrogen ions in the body
A
- High concentration of H+ = low pH.
- H+ ions interact with H-bonds & ionic bonds in tertiary structure of proteins, which can cause them to denature
24
Q
Explain the role of iron ions in the body
A
- Fe2+ bonds to porphyrin ring to form haem group in haemoglobin.
- Haem group has binding site to transport 1 molecule of O2 around body in bloodstream.
- 4 haem groups per haemoglobin molecule.
25
Explain the role of sodium ions in the body
Involved in co-transport for absorption of glucose & amino acids in lumen of gut.
26
Explain the role of sodium ions in the body
Involved in co-transport for absorption of glucose & amino acids in lumen of gut.
27
Explain the role of phosphate ions in the body
DNA
ATP
28
What is the general structure of an amino acid?
-COOH (carboxyl) group
-R variable side group
-NH2 (amine) group
29
Describe how to test for proteins in a sample
1. Add equal volume of sodium hydroxide to sample at room temperature.
1. Add drops of dilute copper (II) sulfate solution. Swirl to mix.
1. Positive result: colour changes from blue to purple
30
How many amino acids are there and how do they differ from one another?
20
differ by R group
31
How many levels of protein structure are there?
4
32
Define the primary structure of a protein
* Sequence, number & type of amino acids in the polypeptide
* Determined by sequence of codons on mRNA
33
Define secondary structure of a protein
Hydrogen bonds form between O attached to -C=O& H attached to -NH
34
Describe the 2 types of secondary protein structure
Alpha-helix
35
Describe the 2 types of secondary structure
Alpha-helix
* all N-H bonds on same side of protein chain
* spiral shape
* H-bonds parallel to helical axis
Beta-pleated sheet:
*N-H and C=O groups alternate from one side to the other.
36
Define tertiary structure of a protein. Name the bonds present
3D structure formed by further folding of polypeptide
Bonds: disulfide bridges, ionic bonds, hydrogen bonds
37
Describe the structure and function of globular proteins
Spherical and compact
Hydrophilic R groups face outwards & hydrophobic R groups face inwards
Involved in metabolic processes
38
What are enzymes
Biological catalysts
Specific tertiary structure determines shape of active site. Complementary to specific substrate.
Formation of enzyme-substrate (ES) complexes lowers activation energy.
39
Explain the induced fit model of enzyme action
Shape of active site is not directly complementary to substrate & is flexible.
Conformational change enables (ES) complexes to form.
This puts strain on substrate bonds, lowering activation energy.
40
What is in a nucleotide?
Phosphate group, pentose sugar, base
41
Name the pentose sugar in DNA & RNA
DNA: deoxyribose
RNA: ribose
42
State the role of DNA in living cells
Base sequence of genes codes for functional RNA & amino acid sequence of polypeptides.
Genetic information determines inherited characteristics = influences structure & function of organisms.
43
State the role of RNA in living cells
mRNA: Complementary sequence to 1 gene from DNA with introns (non-coding regions) spliced out. Codons can be translated into a polypeptide by ribosomes.
rRNA: component of ribosomes
tRNA: supplies complementary amino acids to mRNA codons during translation
44
How do polynucleotides form?
Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)
45
Describe the structure of DNA
Double helix of 2 polynucleotide strands
H-bonds between complementary bases (A-T & C-G)
46
Relate the structure of DNA to its functions
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 pairing for accurate replication
weak H-bonds break so strands separate for replication
47
Describe the structure of mRNA
Long ribose polynucleotide (shorter than DNA)
Contains U instead of T
Single stranded
48
Describe the structure of tRNA
Single stranded of about 80 nucleotides
Folded into clover shape
Anticodon on one end, amino acid binding site on the other
49
Why is DNA replication described as semiconservative?
Strands of DNA molecule act as a template
New DNA molecule contains 1 old strand and 1 new strand
50
Outline the process of semiconservative replication
1.DNA helicase breaks H-bonds between base pairs
2. Each strand acts as a template
3. Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
4. DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
5. H-bonds reform.
