Biology 2 questions

• What are the functions of the cell membrane?

  - regulates movement of material in and out of the cell

  - involved in cell communication and recognition

  - allows cellular components to have different conditions
• Describe the structure of a cell membrane and what the effects are

  - phospholipids - hydrophobic fatty acid tails and hydrophilic phosphate group heads. Hydrophilic heads have an affinity with water so face towards water, and hydrophilic tails face away

  Bilayer

  Amphipathic due to hydrophilic and phobic nature

  Lipid soluble and non-polar small molecules can pass through
• Why is the cell membrane described with the fluid mosaic model

  Fluid: phospholipid molecules can move laterally freely

  Mosaic: proteins distributed unevenly in a mosaic pattern

  Model: based on experimental and chemical evidence
• Give evidence for the fluid mosaic model

  - rupture causes cell contents to flow out

  - water soluble molecules cannot enter as easily as lipid soluble - membrane is highly composed of lipids

  - fluorescence gene tags show some components are continually moving - 'fluid
• Describe how the cell membrane can be made less fluid

  - increase steroid and cholesterol content

  - decrease amount of unsaturated fatty acids present

  - longer fatty acid tails
• What are the two types of proteins in the cell membrane

  Channel - intrinsic (span whole membrane), can be gated and specific, facilitated diffusion, lined with polar groups to allow charged molecules and ions to pass through

  
  

  Carrier - an be facilitated diffusion or active transport, specific - active site is specific to substrate, when bound to, the protein changes shape and is deposited on the inside, either with ATP or kinetic energy from molecules (if passive)
• Define diffusion


  the passive movement of molecules from an area of high concentration to low concentration until they are spread out evenly
• Fick's Law


  SA X Concentration Gradient / diffusion distance
• Define facilitated diffusion


  the passive movement of molecules across a membrane from high to low concentration via protein channels and carriers
• Define active transport


  the active movement of molecules across a cell membrane from low to high concentration reuiring carrier proteins and ATP
• Define osmosis


  The net movement of water molecules from an area of higher water potential to lower across a partially permeable membrane
• What is water potential?

  Water potential is the tendency of water molecules to diffuse out of or into a solution.

  e.g. a highly concentrated sugar solution has a low water potential and pure water has the highest (0)
• What is endocytosis?

  process by which the cell takes in materials that are too large to pass through the cell membrane or use a protein carrier

  phagocytosis or pinocytosis

  cell membrane pinches in on itself to surround the material and form a vesicle. Lysosomes can fuse with it to digest the large molecules
• What is exocytosis?

  the process where large materials are exported out of the cell via secretory vesicles which fuse with the plasma membrane and expel their contents
• Compare the similarities and differences of endo and exocytosis

  both - active processes, transport macromolecules, vesicles cannot interact with cytoplasm vesicles have phospholipid membranes

  endo - brings in, e.g. engulfing pathogens

  exo - expels, e.g. releasing enzymes
• CPAC: Membrane Permeability (beetroot) effect of temperature or alcohol concentration


  - use a cork borer and cut beetroot into 1cm cylinders

  - place in distilled water overnight to remove excess dye

  - prepare boiling tubes containing 5cm3 water from water baths at 0-60 degC, put beetroot in for 30 mins

  - pour liquid into cuvettes and measure % absorbance with a calorimeter
• Lung adaptations for gas exchange

  - lots of alveoli - large SA to Vol ratio

  - one cell thick epithelial walls - short diffusion distance

  - rich O2 blood supply - steep concentration gradient

  - ventilation - steep concentration gradient

  - alveoli are moist - speeds up particle movement
• How to convert m to nm

  X 10^-9
• How to convert m to um (micrometres)

  X 10^-6
• Briefly describe gas exchange in insects

  spiracles allow gas flow into body cavity

  lots of trachioles close to body cells for short diffusion distance

  spiracles open or close depending on o2 supply
• Briefly describe gas exchange in fish

  - gills are feathery and thin, spreading out in water to provide a large SA for diffusion

  - counter current flow maintains a concentration gradient
• What elements are proteins made of?

  carbon

  hydrogen

  oxygen

  nitrogen
• Describe the basic structure of amino acids

  - amino group (NH2)

  - carboxyl group (COOH)

  - R group which differs in length
• Describe how amino acids join to form proteins

  - condensation reactions

  - amino group and carboxyl group of two amino acids form a bond

  - peptide bond

  - water produced
• Describe protein primary structure

  - the unique and specific sequence of amino acids that make up a polypeptide chain, held together by peptide bonds

  - condensation reaction

  - determines the eventual shape and function of the protein
• Describe protein secondary structure

  The way in which the primary structure folds

  Hydrogen bonds

  Alpha helix - regular coiled structure, R groups face outwards, strong and stable yet still flexible and elastic

  Beta pleated sheets - composed of chains side by side, connected with H bonds

  Inter-chain linkages make a very stable structure
• Describe protein tertiary structure

  - the overall 3D structure of the protein due to the complete folding of the sheets and helices

  H bonds

  Disulphide bridges

  Ionic Bonds

  Hydrophobic and hydrophilic interactions
• Globular protein structure and example

  compact, ball shaped, due to highly twisted polypeptide chains

  Hydrophobic R groups from some and hydrophilic groups from other amino acids face outwards to make globular proteins water soluble

  relatively unstable but shape can allow them to have active sites/specific receptor binding sites e.g. enzymes, antibodies and hormones

  Haemoglobin - 4 polypeptide chains held together with disulphide bridges, centre contains an Fe2+ haem group

  each molecule of haemoglobin can carry 4 O2 molecules in a reversible binding reaction to form oxyhaemoglobin
• Describe fibrous protein structure and an example

  parallel polypeptide chains, linked together to form long fibres

  very strong due to inter-chain bonding

  insoluble in water, little-no tertiary structure

  structural functions

  Collagen - structural protein providing strength in tendons and bones

  3 polypeptide chains twisted to form a helix - helices wind round each other to form a triple helix, held together by H bonds
• Describe the induced fit model of enzyme action

  the enzyme has flexibility and the active site does not directly fit with the substrate - it moulds itself to fit
• CPAC: Effect of Enzyme concentration on Initial Rate of Reaction

  - potato cylinders and hydrogen peroxide

  - beaker of warm water/ in water bath

  - measure O2 released using a measuring cylinder submersed in water

  - use a different number of potato disks each time - alters the concentration of catalase
• Describe the structure and formation of DNA

  - condensation reaction forms phosphodiester bonds between a pentose sugar and phosphate group

  Backbone: phosphate group, pentose sugar (phosphodiester bonds between), H bonds connect nitrogenous bases to the backbone

  complementary base pairs: A=T C-=G(triple bond)

  Antiparallel strands

  contains deoxyribose pentose sugars
• DNA and RNA differences

  1. DNA is double stranded, RNA is single stranded

  2. RNA has a ribose sugar, DNA has a deoxyribose sugar

  3. Thymine base pair in DNA is replaced by Uracil in RNA
• Describe bacterial DNA

  - large and circular

  - in cytoplasm

  - no nucleus

  - plasmids

  - DNA not associated with histone proteins
• Describe the process of semi-conservative DNA replication

  - DNA helicase causes the H bonds to break to separate the 2 DNA strands

  - each strand is used as a template and DNA polymerase binds to the promotor region

  - it catalyses the formation of complementary chains of nucleotides with phosphodiester bonds

  - leading strand, a continuous strand of DNA is made

  - lagging strand - one section at a time is made, and they are then joined together with DNA ligase

  - 2 identical copies of the original DNA molecule
• Describe the Meselson-Stahl experiment


  E. coli bacteria grown in a medium with heavy isotope of nitrogen (N15)

  After several generations the nitrogenous bases of the bacterial DNA were labelled with the N15 isotope

  When switched to a medium containing the lighter N14 isotope, the bacteria were allowed to divide for a few generations

  centrifugation formed density gradients to show which isotopes were present in the DNA

  gen 0 = DNA only contained N15, single band produced

  gen 1 = DNA produced a single higher band

  gen 2 = 2 distinct bands, one at the same place as gen 1, and one higher - some DA had N14 and 15 and others only had N14 - suggested semi-conservative replication was the most likely
• What is a gene?


  a hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism
• Allele?

  a variation of a gene
• What is meant by 'triplet code'?

  3 base pairs code for one amino acid, each set of 3 bases is called a codon

  one codon codes for 1 amino acid
• Types of RNA


  mRNA - messenger during transcription

  tRNA - transfer during translation

  rRNA - ribosomal - makes ribosomal proteins used in translation