biological molecules Flashcards
What are the two types of proteins
Fibrous and globular
What are the three uses of proteins
Growth, repair of tissues and replacement of cells
How many types of amino acids are there
20
Plants can make all their proteins themselves but what do they need for this
nitrogen in the form of nitrates in the soil
Describe the general structure of an amino acid
Has an amino group NH2
A representative group R
A carboxyl group COOH (O is double bonded)
H R O
\ | //
N- C -C
/ | \
H H OH
What forms a peptide bond
A condensation reaction
O H
|| | plus H2O
C—–N
Describe the biuret test
- mix 1 cm3 of solution with an equal volume of biuret solution
- Swirl tube
- Observe colour change blue to lilac if present
Why does biuret test work
chemicals in biuret react with peptide bonds
What is a proteins primary structure
The specific sequence of amino acids determined by bases/genetic code (DNA)
Joined by peptide bonds
What is secondary structure
How a polypeptide folds
Will form either an alpha helix (keratin) or beta pleated sheet (silk)
Secondary structures are stabilised by hydrogen bonds
(there are parts of a poly peptide with no secondary structureand just join sheets and helices together)
What is tertiary structure
the 3d structure of a protein that determines the way a helices and B pleated sheets interact with each other
Held together by 4 types of bonds: disulfide
Ionic bonds
hydrogen bonds
Hydrophobic/phillic interactions
What is quaternary structure
Not all proteins have this but all with two or more polypeptide chains will
What are conjugated proteins
Proteins containing a non protein part/ prosthetic group. These can be attactched by covalent or hydrogen or ionic bonds.
Haem group of haemoglobin
Describe the function and structure of globular proteins
Roll into balls to form speheres
Primary structure is very precise and usually non repeating
secondary and tertiary structures are complex
Usually water soluble (hydrophilic R groups point out)
They are usually have metabolic and immune uses or for muscle contractions.
Enzymes insulin and hormones
Describe the function and structure of fibrous proteins
Form long narrow fibres
Often have long simple repeating amino acid sequences for primary structures
Have simple secondary and tertiary structures
Usually insoluble
Usually have structural uses
How is collagen’s molecular structure related to its function?
Fibrous
Triple Helix: Three polypeptide chains (α-chains) twist into a right-handed triple helix, stabilized by hydrogen bonds.
Glycine-X-Y Repeats: Glycine (smallest amino acid) at every third position allows the chains to pack tightly. X and Y are often proline and hydroxyproline, which stabilize the helix.
Cross-linking: Collagen fibrils are reinforced by covalent cross-links between lysine residues, giving them strength.
Relation to Function:
Tensile Strength: The triple-helix and cross-linking provide high tensile strength, essential for structural integrity in tissues like tendons, ligaments, and skin.
Flexibility: Despite its strength, the glycine content allows for some flexibility.
Support: Collagen forms fibers and networks that support tissue structure (e.g., cartilage, bone matrix).
How is keratin’s molecular structure related to its function?
Fibrous
Alpha-Helix (α-keratin): Coiled polypeptide chains form a right-handed alpha-helix. Two helices twist together into a coiled-coil.
Disulfide Bonds: Cysteine residues form strong disulfide bonds between polypeptide chains, adding rigidity and stability.
Intermediate Filaments: Multiple coiled-coils assemble into protofilaments and protofibrils, forming strong fibers.
Relation to Function:
Mechanical Strength: The coiled-coil structure and disulfide bonds provide tensile strength and resistance to mechanical stress, ideal for hair, nails, and outer skin layers.
Flexibility vs. Hardness: High disulfide bond content increases hardness (e.g., nails), while lower content allows flexibility (e.g., skin).
Protection: Keratin forms a protective barrier against environmental damage, dehydration, and pathogens.
How is elastin’s molecular structure related to its function?
fibrous
Hydrophobic Domains: Elastin contains hydrophobic amino acids (e.g., glycine, valine, alanine) that drive coiling and recoil, allowing elasticity.
Cross-Linking: Lysine residues form covalent cross-links (desmosine and isodesmosine) between elastin molecules, stabilizing the network.
Amorphous Structure: Unlike collagen, elastin does not form a rigid, ordered structure but instead creates an amorphous, flexible network.
Relation to Function:
Elasticity: The hydrophobic regions and cross-linking allow elastin to stretch and return to its original shape, enabling tissues like lungs, arteries, and skin to recoil.
Resilience: The combination of flexibility and cross-linked stability ensures durability under repeated mechanical stress.
Tissue Flexibility: Elastin provides essential elasticity to tissues that need to expand and contract repeatedly (e.g., blood vessels, lungs)
How is hemoglobin’s molecular structure related to its function?
Quaternary Structure: Hemoglobin is a tetramer composed of 4 polypeptide chains (2 alpha and 2 beta chains). Each chain contains a heme group.
Heme Group: Contains an iron (Fe²⁺) ion that reversibly binds oxygen molecules.
Cooperative Binding
Oxygen Transport: The heme groups enable hemoglobin to bind and transport oxygen from the lungs to tissues.
Oxygen Release: Cooperative binding and allosteric effects allow efficient oxygen release where it is needed (e.g., tissues with low oxygen levels).
CO₂ Transport: Hemoglobin also helps carry CO₂ and protons back to the lungs for exhalation, aiding in pH regulation.
How is insulin’s molecular structure related to its function?
Two Polypeptide Chains: Insulin consists of an A-chain (21 amino acids) and a B-chain (30 amino acids), connected by two disulfide bonds. An additional disulfide bond is within the A-chain.
Tertiary Structure: The precise folding and disulfide bridges stabilize the structure, ensuring proper receptor binding.
Proinsulin Precursor: Insulin is initially synthesized as proinsulin, which is cleaved to release active insulin.
Soluble in blood plasma
Relation to Function:
Receptor Binding: The specific 3D structure enables insulin to bind to the insulin receptor on target cells, triggering glucose uptake.
Glucose Regulation: Insulin regulates blood glucose levels by promoting glucose storage as glycogen (liver, muscles) and uptake into cells.
Stability: The disulfide bonds ensure structural stability, allowing insulin to function effectively in the bloodstream.
How is pepsin’s molecular structure related to its function?
Molecular Structure:
Globular Protein: Pepsin is an aspartic protease with a compact, folded structure optimized for activity in acidic environments.
Active Site: Contains two critical aspartic acid residues that facilitate proteolysis by activating water molecules to break peptide bonds.
pH Dependence: The structure is stable and active at low pH (1.5–2), which is essential for gastric digestion.
No quaternary structure
Only made from 4 basic R groups
Relation to Function:
Protein Digestion: The active site and acidic stability allow pepsin to break peptide bonds in dietary proteins into smaller peptides.
Stability in Stomach: Pepsin’s structure ensures optimal function in the acidic gastric environment.
Stability in low ph
What is Thin Layer Chromatography (TLC)?
TLC is a technique used to separate and identify components in a mixture. It involves a stationary phase (a thin layer of adsorbent material) and a mobile phase (a solvent or mixture of solvents) that moves through the stationary phase by capillary action.
What materials are used in the stationary and mobile phases in TLC?
Stationary Phase: A thin layer of adsorbent material (e.g., silica gel or alumina) coated onto a solid surface like glass, plastic, or aluminum.
Mobile Phase: A solvent or solvent mixture (e.g., ethanol, acetone) that carries the sample components up the plate
What is the Rf value, and how is it calculated?
The Retention Factor (Rf) is a measure of how far a compound travels relative to the solvent front:
𝑅
𝑓
=
Distancemovedbythecompound over
Distancemovedbythesolventfront
Rf values are unitless and range between 0 and 1
