3 - Biological Molecules Flashcards
Define polar
Regions of negativity and positivity
Polarity in covalent bonds.
In covalent bonds, atoms share electrons. But electrons are not always shared equally by atoms of different elements.
Electrons spend more time closer to one of the atoms than the other.
Atoms with the greatest share of electrons = slightly negative (f-)
Atoms with less a share of electrons = slightly positive. (f+)
Describe structure of water
It is a polar molecule.
H2O
Oxygen and hydrogen don’t share electrons equally in covalent bonds. Oxygen always has greater share of electrons in O-H bond. Many organic molecules are slightly polar
What are hydrogen bonds?
Polar molecules interact with each other as positive and negative regions of molecule attract each other and form hydrogen bonds.
Relatively weak -> break and reform between constantly moving water molecules.
But occurs in high numbers so requires high energy to overcome.
Describe some characteristics of water
1) unusually high BP - SHC + SLV (specific latent heat of vaporisation)
Small molecule, liquid @ room temperature due to hydrogen bonds b/w molecules -> more energy to increase temperature of water and evaporate it
2) adhesive properties. Water molecules attracted to other materials. When you wash hands they become wet and water does not run straight off.
3) cohesive properties. Moves as one mass because molecules are attracted to each other. So plants can draw up water from roots + you can drink from a straw
4) surface tension. water molecules more strongly cohesive to each other than to air
5) less dense in solid state. As water is cooled <4°C H bonds fix positions of polar molecule slightly further apart than average distance in liquid state. This creates a giant, rigid, open structure where every O atom is at the centre of a tetrahedral arrangement of H atoms.
How is water vital for life?
1) acts as a SOLVENT where many solutes in bacteria dissolve. Cytosol of prokaryotes and eukaryotes are mainly water.
- Also acts as a medium for chemical reactions.
- Also helps transport dissolved compounds in or out of cells.
2) stable habitat for organisms. Does not change temperature or turn into gas easily = constant environment. Ice floats and forms on surface of ponds & lakes creating an insulating layer for water below. This allows aquatic organisms to survive in non-freezing temperatures than if ice formed @ bottom.
- Surface tension is strong enough to support small insects like pond skaters.
3) Acts as a coolant. Buffers temperatures during chemical reactions in cells due to increased energy needed to overcome H bonds.
- maintains constant temperature is in cellular environments as enzymes often active in narrow temperature range.
4) it is an efficient transport medium. Molecules stick together inside the body due to cohesion. Adhesion allows water molecules to be attracted to other polar molecules on surfaces. Exhibits capillary action: water rises up narrow tube against force of gravity
Why can you not compress water to a higher degree?
because like charges will start to repel
How is a peptide bond broken?
Hydrolysis reaction
Water is needed
What contains ester bonds?
Triglycerides and phospholipids.
Cholesterol does not contain ester bonds
Describe how to do emulsion test for lipids and how a positive result is identified.
Add ethanol
Goes cloudy / milky white
How might Lipid content of mycoprotein (produced by microorganisms) differ from food that comes from animals?
less lipid content overall.
lipid in mycoprotein is less saturated than lipids that come from animals
Describe the structure of a collagen molecule
- peptide bonds between amino acids
- every 3rd amino acid is glycine; smallest amino acid, allows collagen to pack together tightly
- 3 polypeptide chains
- glycine / small R group allows twisting of chains
- coils/twist to left handed helix
- hydrogen bonds present between chains
- few hydrophilic R groups on outside
- adjacent molecules joined by cross links (which are staggered)
- form fibrils
Describe 3 ways structure of haemoglobin differs from that of collagen
- Haemoglobin is globular
- Haemoglobin has 4 polypeptide chains
- Haemoglobin has alpha helix structure/ subunits
Describe formation of peptide bond
Formed in condensation reaction which occurs between H from amine group of one amino acid and OH from carboxyl group of another amino acid. Water is also produced
Three examples of where hydrogen bonds are found in biological molecules
- Secondary structure of protein
- Between polypeptide chains in collagen
- Between chains of cellulose
- Between starnds of bases in DNA
- Tertiary protein structure
