chemical composition of cells

• property of water - cohesion

  • water molecules being attracted to each other due to forming attractive hydrogen bonds
  • surface tension: ability of the surface of a liquid to resist external force (eg. insects walking on water)
• property of water - high specific heat capacity

  • water has a high SHC due to hydrogen bonding
  • C = amount of energy that causes 1g of water to increase by 1°C

  A) vaporisation

  B) fusion

  C) liquid

  D) gas

  E) solid

  
• properties of water - relative density of water and ice

  • ice floats on water due to its stable H-bond structure (lattice-like), unlike water's transient H-bond structure which is more messy
  • this means ice is less dense than water

  
• properties of water - water as a solvent

  • water can form H-bonds and dipole dipole interactions with other molecules, these molecules are hydrophilic (water loving)
  • water dissolves polar molecules
  • here, Na+ is attracted to the partially negatively charged oxygen atoms, splitting NaCl (dissolving)

  
• non polar molecules are hydrophobic

  • the C-H bond is barely polar due to a low electronegativity difference between C and H
  • thus, no dipole dipole interactions occur between water and the non polar molecule
• pH relating to water

  • as the [H+] decreases, the pH increases (more basic) as H+ is a proton donor making it acidic, so less acidity = higher pH

  
• ionisation states of alanine (amino acid)

  • at a low pH (acidic), alanine will gain a H, making the N positively charged

  A) isoelectric

  B) 50

  
• impact of pH on enzyme activity

  • enzymes have specific optimal pH's, a change in pH can hinder its ability to function properly
  • denatures the protein: changes the 3D active site so the enzyme is no longer useful
• buffers

  • a mixture of a weak acid and its conjugate base in equal amounts to resist changes in pH caused by adding H+ or OH-
  • eg. when adding H+, to resist a large pH change its conjugate base must also be added
  • this will help to buffer any change in pH

  
• nucleic acids

  • DNA and RNA are polymers of nucleotides
  • nucleotides are made up of 3 components

  A) nitrogenous

  B) sugar

  C) phosphate

  D) T

  
• "phosphodiester bonds" link nucleotides

  • to link nucleotides, a condensation reaction occurs with DNA polymerase
  • the hydrogyl group on the C5 end reacts with the Hydrogen on the C3 group to form water and creates a link at the phosphate group
  • DNA is written from 5' to 3'
  • this sequence is TAA (not AAT)

  
• DNA is made up of DEOXYribonucleotides

  • deoxy adenosine monophosphate
  • deoxy guanosine monophosphate
  • deoxy thymidine monophosphate
  • deoxy cytidine monophosphate

  A) RNA

  
• DNA consists of 2 complementary strands

  • one strand = sense strand (eg. A - T , C - G)
  • other strand = anti-sense strand (eg. T - A , G - C)
  • the antisense strand is reverse complement to the sense
  • the strands are connected by hydrogen bonds

  A) base pair

  
• why does DNA form a double helix structure

  • H-bonding between base pairs: h-bonds between A-T and C-G
  • base pair stacking: hydrophobic effect (removing water) creates a stacking effect, hence the coiling
• phospholipids

  • phospolipid= glycerol + 2 fatty acids + phosphate
  • hydrophilic: attraction to wate (ie. polar)
  • amphipathic = hydrophilic phosphate head + hydrophilic fatty acid tail

  A) phosphate

  B) glycerol

  C) head

  D) hydrophilic

  
• membranes - phospholipid bilayers

  • hydrophobic tails are shielded from water: they are non-polar
  • hydrophilic heads are exposed to water: they are polar
  • as such, the hydrophobic core prevents water soluble substances and ions passing through the membrane, whilst the hydrophilic head prevents water insoluble substances from passing through the membrane.

  
• levels of structures in a cell

  A) plasma membrane

  B) protein

  C) amino acids

  D) nucleotides

  
• disaccharides

  • maltose = glucose + glucose
  • sucrose = glucose + fructose
  • lactose = glucose + galactose

  A) sucrose

  B) maltose

  C) lactose

  
• monosaccharides (C6H12O6)

  • glucose
  • fructose
  • galactose

  A) glucose

  B) fructose

  C) galactose

  
• D vs L glucose

  • they are stereoisomers of each other (ie. mirror images of each other / enantionmers)
  • D : hydroxyl group on chiral carbon is furthest away from C=O
  • L: hydroxyl group on chiral carbon is closest to C=O
  • D is more common

  A) D

  B) L

  
• a vs b glucose

  • alpha: hydroxyl group on first carbon goes down
  • beta: hydroxyl group on first carbon goes up

  A) a

  B) b

  
• types of polysaccharides

  • homo: made up of the same sugar
  • hetero: made up of different sugars
  • both homo and hetero can be branched and unbranched

  
• starch

  • function being the marjor energy storage in plants : excess glucose from photosynthesis is polymerised into starch
  • contains amylose and amylopectin
  • stored as granules in the chloroplast of plant cells
  • can have 500-20,000 glucose units
• cellulose

  • function: gives rigid and strong structure for cell wall from the linear/unbranched chain due to H-bonds (ie. microfibrils)
  • made up of b-glucose

  
• chitin

  • function: big role in the exoskeleton of insects, crustaceans (eg. crab) and cell walls of fungi
  • structure: made of N-acetylglucosamine (GlcNAc) units
  • provides structural support and protection, it feels hard
  • chitin = (b-glucose + acetyl group ) n

  
• peptidoglycan

  • function: provide structural support to bacteria's cell wall
  • peptidoglycan = glycan chain (polysac.) + protein
  • glycan chain: alternating NAG & NAM sugars
  • protein: short chain (~5 amino acids)
  • the protein is cross linked with the glycan chain

  A) NAG

  B) NAM

  
• extracellular polysaccharides - glycosaminoglycans (GAG)

  • heteropolysaccharides: chain of different sugars
  • amino-containing sugar : type of sugar with amino group (-NH2)
  • GAG = disaccharide + uronic acid

  
• glycoproteins

  • Protein chains with covalently linked sugar chains
  • Can be intracellular or membrane bound
  • found on the cell surface

  
• proteoglycans

  • consist of mostly carbohydrates and a core protein to which long chains of polysaccharides are covalently linked
  • providing structural support to tissues
• proteins' functions

  • enzyme
  • structural support
  • makes up hormones
  • makes antibodies, protects against disease
  • act as transporters inside and outside cells
• secondary structures of proteins - overall 3D shape of protein

  • a-helix: H-bonds between O (C=O) on one amino acid and the H (CONH) on another acid but same chain
  • b-pleated: H-bonds between O (C=O) the H (CONH) but from different chains

  
• tertiary structure - myoglobin

  • function: supplies oxygen to cells in muscles
  • found in muscle cells
  • stores O2
  • holds an oxygen binding haem group in specific pocket

  
• quarternary structure - haemoglobin

  • function: carries oxygen throughout the body
  • found in red blood cells, makes red colour
  • made up of 4 proteins each binding to oxygen