Biology

• large molecules often contain carbon. why?


  they can readily form bonds with other carbon atoms. this forms a 'backbone'. other atoms can then attach.
• describe benedicts test for reducing sugars

  add equal volumes of the sugar sample and benedicts reagent.

  heat the mixture in a water bath for 5 minutes.

  brick red precipitate will form.
• what is a reducing sugar?

  a sugar that can reduce (give electrons to) another chemical.
• describe the benedicts test for non reducing sugars

  with food sample, add an equal volume of dilute hydrochloric acid in a test tube.

  place test tube in water bath for 5 mins.

  add sodium hydrogencarbonate solution.

  heat resulting solution with an equal volume of benedicts. solution for 5 minutes.

  turns orange/brown.
• what does dilute hydrochloric acid do in the benedicts test for non reducing sugars?

  it hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars.
• describe the structure of starch

  chains of alpha glucose

  some chains are branched= amylopetcin

  some chains are coiled= amylose
• what purpose does the structure of amylose serve?

  makes the molecule compact so it is stored more easily.
• what purpose does the structure of amylopectin serve?

  more surface area for enzymes to work on, thus glucose molecules can be released at a much quicker rate.
• how is the structure of starch suited to its function?

  1. starch is insolube so it doesnt affect water potential

  2. it is large enough that it doesnt diffuse out of cells

  3. compact enough so that a lot of it can be stored in a small space

  4. branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released
• how is the structure of glycogen suited to its function?

  1. insoluble, so no effect on water potential of cell

  2. insoluble, so doesnt diffuse out of cells

  3. compact, a lot of it can be stored in a small space

  4. very highly branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released
• why do animals need highly branched glycogen?

  because animals metabolic rate is faster than plants and so needs glucose to be released quicker.
• describe the structure of cellulose

  made up of straight chains of beta glucose

  the chains are parallel to each other, so H bonds form cross-linkages

  all the H bonds together strengthens the cellulose

  forms microfibrils
• draw alpha and beta glucose

  
• how does the structure of triglycerides relate to their properties?

  1. triglycerides have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms, so its a good source of energy.

  2. low mass to energy ratio, so theyre good energy storage molecules.

  3. large and non-polar, therefore insoluble, therefore don't affect osmosis.

  4. high ratio of hydrogen to oxygen atoms, so can release water when oxidised, hence provide a source of water
• what are the roles of lipids?

  1. source of energy

  2. waterproofing

  3. insulation

  4. protection
• how does the structure of phospholipids relate to their properties?

  1. polar, therefore will position itself to form a bilayer

  2. the structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. these are important in cell recognition.
• draw the structure of an amino acid

  
• draw how a dipeptide forms

  
• what is meant by 'primary sequence' of a protein

  The unique sequence of amino acids that make up a protein or polypeptide chain
• what is meant by 'secondary sequence' of a protein

  The way in which the primary structure of a polypeptide chain folds e.g. alpha helix or beta pleated sheets. shape is held by H bonds.
• what is meant by 'tertiary sequence' of a protein

  This is the overall 3-D structure of the protein.

  The shape of the protein is held together by H bonds and ionic bonds and disulfide bridges.
• what is meant by 'quaternary sequence' of a protein

  If a protein is made up of several polypeptide chains that are linked in various ways, the way they are arranged is called the quaternary structure.
• describe the test for proteins

  add equal volumes of sample and sodium hydroxide (biuret) to a test tube.

  add a few drops of dilute copper (II) sulfate and mix.

  if solution turns purple, protein is present.
• what are fiberous proteins made up of?

  made of long molecules arranged to form fibres (e.g. in keratin). Several helices may be wound around each other to form very strong fibres.
• what are globular proteins made up of?

  made of chains folded into a compact structure. One of the most important classes are the enzymes. Although these folds are less regular than in a helix, they are highly specific and a particular protein will always be folded in the same way.
• what kind of protein is collagen?

  fiberous
• what kind of protein is haemoglobin?

  globular
• what is haemoglobin made up of?

  two α polypeptide chains

  two β polypeptide chains

  an inorganic prosthetic haem group (Fe2+)
• what is collagen made up of? describe its structure?


  three polypeptide chains

  wound around each other

  each of the three chains is a coil itself

  Hydrogen bonds form between these coils

  Collagen molecules form further chains with other collagen molecules and form Covalent Cross Links with each other, which are staggered along the molecules to further increase stability. Collagen molecules wrapped around each other form Collagen Fibrils which themselves form Collagen Fibres.
• what are the functions of collagen?

  1. Form the structure of bones

  2. Makes up cartilage and connective tissue

  3. Prevents blood that is being pumped at high pressure from bursting the walls of arteries

  4. Is the main component of tendons, which connect skeletal muscles to bones
• what type of bond forms between the phosphate group and deoxyribose sugar in DNA?

  phosphodiester bond
• why is DNA stable?

  1. the phosphodiester backbone protects the more

  chemically reactive organic bases inside the double helix

  2. many hydrogen bonds link the base pairs together, so it adds strength overall.
• how is DNA adapted to carrying out its function?

  1. it is very stable, thus rarely mutates

  2. the H bonds can easily be separated during DNA replication and protein synthesis

  3. extremely large, thus carries a lot of genetic information

  4. base pairing allows DNA to replicate and transfer info as mRNA.
• describe semi conservative replication

  - DNA helicase unwinds separates the two strands of DNA into single strands by breaking the H bonds between the bases

  - this therefore forms 2 base templates (the bases on each strand are exposed)

  - free complimentary nucleotides align with the bases according to complimentary base pairing

  - they are joined via condensation reaction with DNA polymerase

  - the new DNA molecule is formed
• what is meant by resolution

  the minimum distance apart that two objects can be in order for them to appear as separate items.
• before cell fractionation, why is the tissue placed in a cold, isotonic buffer?

  cold: reduce enzyme activity that may break down the organelles

  isotonic: same water potential as tissue, this prevents organelles shrinking/bursting due to osmotic loss/gain of water

  buffered: so the pH doesn't fluctuate, so that nothing alters the organelle structures or affects enzyme functioning
• what are the advantages of an electron microscope?

  electron beam has a short wavelength and the microscope can therefore has high resolution.

  the negatively charged beam can be focused using electromagnets.
• what are the limitations of using a transmission electron microscope?

  the whole system must be in vacuum, so living specimens cant be studied.

  complex staining process

  the image may contain artefacts
• what is the function of SER?

  synthesises, stores and transports lipids and carbohydrates
• what is the function of RER?

  provides a large surface area to synthesise proteins and glycoproteins

  provides a transport pathway for materials throughout the cell