Chapter 3: Biological Molecules Flashcards
1
Q
Structure of Globular Proteins.
A
- Spherical + 3D tertiary structure + pH/temp sensitive.
- Hydrophobic R groups on inside + hydrophilic R groups on inside.
- Forms H-bonds with water –> soluble.
E.g. Haemoglobin, catalase, insulin, channel/carrier proteins, fibrinogen (involved in blood clotting.
- Haemoglobin –> carries O2 –> contains prosthetic haem group with Fe2+ ions –> polypeptide chains within haemoglobin have tertiary structure.
2
Q
Structure of Fibrous Proteins.
A
- Linear.
- Chains form H-bonds with adjacent molecules.
- Insoluble + few hydrophilic R groups + unreactive.
- Strong + long/elongated.
- Have structural role + flexible.
E.g. collagen, keratin, elastin.
Collagen:
- -> High proportion of glycine so chains lie close together.
- -> Forms crosslinks between molecules.
- -> Crosslinks staggered to avoid weak points.
- -> Forms part of tendon/connective tissue.
3
Q
Structure of Haemoglobin (Hb).
A
- Sequence of amino acids joined by peptide bonds.
Secondary Structure:
- Alpha helix.
- Small regions of beta pleated sheet.
- H-bonds.
Tertiary Structure:
- Polypeptide chain undergoes further folding.
- 3 bonds.
- Hydrophilic R groups on outside.
- Hydrophobic R groups on inside.
- Ionic bonds.
- Disulphide bonds.
Quaternary Structure:
- 4 polypeptide chains.
- 2 alpha + 2 beta sub-units.
- 1 haem group per sub-unit.
- Prosthetic haem –> contains Fe2+ –> combines reversibly with O2 molecule.
4
Q
Structure of Collagen (fibrous).
A
- Peptide bonds between amino acids.
- Every third amino acid is the same.
- Helix.
- Left handed helix.
- Small R-groups allow twisting of polypeptide chain.
- Few hydrophilic R-groups on outside of molecules.
- Adjacent molecules joined by staggered cross links.
- Fibril.
5
Q
Similarities between collagen and haemoglobin.
A
- Amino acid sequence.
- Peptide bonds.
- Helix.
- 3 bonds.
- Quaternary structure.
- More than one polypeptide.
6
Q
Difference between amylose and cellulose.
A
Amylose:
- Coiled.
- Alpha glucose.
- All monomers in same orientation.
- Granular.
- H-bonds within molecule.
Cellulose:
- No coiling.
- Beta glucose.
- Alternate monomers are at 180 degrees to each other.
- Fibrous.
- H0bonds between adjacent molecules.
7
Q
Reducing sugar test using colorimeter?
A
- Place reducing sugar in boiling tube + heat gently with few drops of Benedict’s reagent.
- Colour changes to brick red –> high reducing sugar conc.
- Filter to obtain precipitate.
- Calibrate colorimeter using unreacted Benedict’s.
- Use red filter.
- Read absorbance.
- Less absorbance –> more reducing sugar present.
- Plot graph of absorbance against conc.
- Obtain calibration curve.
- Read across y-axis and down to x-axis to obtain conc.
8
Q
Iodine test for starch.
A
- Few drops of iodine dissolved in potassium iodide solution are mixed with a sample:
- If solution changes colour from yellow/brown to purple/black starch is present.
9
Q
Biuret test for proteins.
A
- Liquid sample mixed with an equal vol of sodium hydroxide solution.
- Copper sulfate solution (Biuret’s reagent) added a few drops at a time until sample solution turned blue.
- Solution mixed and left to stand for 5 mins.
- Goes lilac/purple –> protein present.
- Stays blue no protein present.
- Amino acid –> stays blue –> no peptide bonds.
10
Q
Emulsion test for lipids.
A
- Sample mixed in ethanol.
- Resulting solution mixed with water + shaken.
- If white emulsion forms (cloudy) as a layer on top of the solution this indicates presence of lipid.
- Solution remains clear –> test is negative.
11
Q
Steps of transcription (nucleus).
A
- DNA transcribed onto RNA.
- Free RNA nucleotides align.
- Complementary base pairing.
- One strand acts acts as the template for the formation of a new strand.
- Catalysed by RNA polymerase –> phosphodiester bonds form between RNA polymerase and RNA nucleotides.
12
Q
Steps of translation (cytoplasm).
A
- mRNA moves to ribosomes.
- tRNA with complementary anticodon binds to mRNA codon.
- Specific amino acid attached to tRNA.
- Peptide bonds form between amino acids.
13
Q
Role of mRNA.
A
Carries complementary DNA copy out of nucleus and transfers it to ribosomes for protein synthesis.
14
Q
Steps of DNA replication.
A
- Semi conservative replication.
- DNA helicase unwinds DNA double helix.
- H-bonds between bases break.
- Each strand acts as template for formation of new molecule.
- Free nucleotides align.
- Complementary base pairing occurs.
- H-bonds reform.
- Sugar phosphate backbone forms.
- DNA polymerase joins the backbone.
- DNA winds into double helix.
- New molecule has 1 new and 1 old strand.
15
Q
Forming a polynucleotide.
A
- Condensation reaction between nucleotides.
- Phosphodiester bonds form between phosphate group (at 5C) of one nucleotide and -OH group (3C) of another nucleotide.
- Sugar phosphate backbone forms.
