topic 1 - biological molecules Flashcards
Explain how the structure of DNA is related to its functions
- DNA is strong as it has a sugar phosphate backbone which protects organic bases from chemical attack
-It is a helical structure so is compact
-Long molecule so can store lots of information
-Base sequence allows information to be stored
-Double stranded so seperate strands can act as templates to replicate DNA
-Weak hydrogen bonds for replication
Where do hydrogen bonds occur between DNA molecules
Between deoxyribose
Give two differences between the structures of DNA and RNA
DNA contains deoxyribose, RNA contains ribose
DNA contains thymine base, RNA contains uracil base
Give two features of DNA and explain how each one is important in the semi conservative replication of DNA
-Weak hydrogen bonds mean strands can easily seperate
-Two strands so both can act as templates
Name the type of bond that forms between the 3rd and 5th carbons on deoxyribose and the phosphate
Phosphodiester
Describe DNA helicase’s function
Breaking hydrogen bonds between strands of DNA
Describe DNA polymerase’s function
Joins nucleotides
catalyses condensation reactions
Describe structure of DNA
-Polymer of nucleotides
-Each nucleotide formed from deoxyribose, phosphate and nitrogenous base
-Phosphodiester bonds between nucleotides
-Double helix held together by weak hydrogen bonds
-Hydrogen bonds between adenine,thhmine and cytosine,guanine
Describe how DNA is replicated
1) Hydrogen bonds break and strands seperate
2) with enzyme DNA helicase
3) Each strand acts as a template
4) Free nucleotides attach
5) Complementary
6) DNA polymerase joins nucleotides
7) Hydrogen bonds reform
8) Semi conservative replication
Name the protein associated with DNA in a chromosome
Histone
Describe how a phosphodiester bond is formed between 2 nucleotides within a DNA molecule
Condensation reaction (loss of water) between deoxyribose and phosphate which is catalysed by DNA polymerase
what is a monomer
a small repeating unit that makes up a polymer
examples of a monomer
glucose, amino acids and nucleotides
what is a polymer
molecules made from a large number of monomers joined together
what is a condensation reaction
joining 2 molecules together with the formation of a chemical bond and releases a water molecule
what is a hydrolysis reaction
breaks a chemical bond between 2 molecules involving the use of a water molecule
what is a carbohydrate
molecules that consist of only carbon, hydrogen and oxygen that are long chains of sugar units called saccharides
what bond is formed between monosaccharides
glycosidic
glucose+glucose
maltose
glucose+galactose
lactose
glucose+fructose
sucrose
is the right OH on alpha glucose at the top or bottom
bottom
properties of glycogen
-alpha glucose monomers
-1,4 and 1,6 glycosidic bonds
-large number of side branches
-large but compact molecule
-insoluble therefore doesn’t affect water potential of cells and cannot diffuse out
properties of starch (amylose and amylopectin)
amylose- 1,4 glycosidic bonds, unbranched therefore it is coiled so very compact
amylopectin- 1,4 and 1,6 glycosidic bonds, branched so can be broken down quickly
properties of cellulose
-beta glucose
-long unbranched chains
-microfibrils form across parallel chains (strong hydrogen bonds)
how does cellulose stop the cell wall from bursting
it exerts inwards pressure that stops the influx of water
reducing sugar test
- add equal amounts food sample and Benedicts solution
-heat in water bath, turns from blue-> brick red ppt
non reducing sugar test
-reducing sugar test first
-add equal parts food sample to HCl and place in water bath (hydrolyses disaccharides)
-add sodium hydrogen carbonate to neutralise (check pH with pH paper)
-redo reducing sugar test with new solution
test for starch
add iodine in potassium iodide
turns from orange/brown to blue/black
what is a lipid
molecules made of only hydrogen, carbon and oxygen which are only soluble in organic solvents e.g alcohols
what are triglycerides made up of
1 glycerol and 3 fatty acids
what are the bonds in triglycerides called
ester
what is a saturated lipid
found in animal fats - don’t contain any carbon-carbon double bonds
what is an unsaturated lipid
found in plants - contain one or more carbon-carbon double bond meaning the molecule can bend (liquid at room temp)
triglyceride structure points to link to its properties
1) high ratio of energy storing carbon-hydrogen bonds to carbon atoms - good energy store
2) low mass to energy ratio meaning a lot of energy is stored in a small volume
3) large and non polar-> insoluble in water so water potential of cells not affected
4) high ratio of hydrogen-oxygen atoms so triglycerides release water when oxidised
what is a phospholipid made up of
1 glycerol, 2 fatty acids and a phosphate group
what is a micelle
many phospholipids in water (heads facing out and tails in)
phospholipid structure points in relation to its properties
1) in an aqueous environment being polar means a bilayer can be formed
2) hydrophilic heads can be used to hold at the surface of the cell surface membrane
3)can form glycolipids with carbohydrates which are important on the cell surface membrane for cell recognition
emulsion test
-add 2cm of sample and 5cm of ethanol
-shake test tube to dissolve lipid
-add 5cm water and shake gently
-cloudy white colour is positive
what are amino acids made up of
amino group (NH2) carboxylic group (COOH) and R group
what bond joins amino acids to make proteins
peptide
what is the primary structure of a protein
order and number of amino acids in a protein
what is the secondary structure of a protein
shape of amino acid chain (alpha helix or beta pleated sheet) formed from weak hydrogen bonds from amine to carboxylic acid groups
what is the tertiary structure of a protein
3d shape of protein formed from bonds forming between R groups
-disulfide bridges (if sulphur in R group)
-ionic bonds
-hydrogen bonds
what is the quaternary structure of a protein
more than one polypeptide
difference between globular and fibrous proteins
globular- compact eg enzymes
fibrous- long to form fibres eg keratin
biuret test for proteins
add equal parts sample and sodium hydroxide
add a few drops copper sulfate, mix gently
blue-> purple is positive
how do enzymes increase rate of reaction
lowering activation energy of reaction they catalyse
describe induced fit model and how enzymes act as a catalyst
substrate binds to active site
active site changes shape slightly so it is complementary to substrate
enzymes reduce activation energy
how does temp affect enzyme controlled reactions
rate increases up to the optimum temp as kinetic energy is increasing. after optimum temp enzymes denature so cannot form ESCs so it drops.
how does pH affect enzyme controlled reactions
pH affects enzymes shape as it can disrupt the bonds in its tertiary structure, so all enzymes have different optimum pH
how does enzyme conc affect enzyme controlled reactions
increases initially as more active sites for substrates to bind to but substrate conc will become a limiting factor
how does substrate conc affect enzyme controlled reactions
more ESCs formed initially so rate increases however all enzymes will eventually be saturated so enzyme conc is a limiting factor
how do competitive inhibitors affect enzyme controlled reactions
inhibitor similar shape to substrate (complementary)
binds to active site
reduces ESCs forming
how do non competitive inhibitors affect enzyme controlled reactions
attaches to enzyme at allosteric site
changes shape of active site
so active site and substrate no longer complementary, no ESCs form
function of DNA
stores genetic information
function of RNA
transfers genetic information to ribosomes for protein synthesis
what is a nucleotide made up of
pentose sugar, nitrogenous base and phosphate
what bonds join nucleotides together
phosphodiester from sugar->phosphate
structure of ATP
ribose, adenine and 3 phosphate groups
what enzyme hydrolyses ATP
ATP hydrolase
properties of ATP making it a suitable energy source
-releases relatively small amount of energy
-releases energy instantaneously
-phosphorylates other compounds making them more reactive
-can be rapidly resynthesized
-is not lost from cells
how is water being a solvent useful and why is water a solvent
so metabolic reactions can occur and because its polar
how does water having a high specific heat capacity make it useful
can gain energy without changing temperature, so buffers changes in temperature
how does water having a large specific latent heat of vaporisation make it useful
evaporation of water provides a cooling effect eg sweating
what do hydrogen ions do
determine the pH of substances eg blood
what do iron ions do
haemoglobin binds, associates with oxygen
what do sodium ions do
cotransport of glucose and amino acids as sodium is moved out by sodium potassium pump
what do phosphate ions do
affects water potential
joins nucleotides
produces ATP
what are ribosomes made of
RNA and proteins
how could you measure the quantity of reducing sugar in a solution
colorimeter to measure absorbance
filter and dry ppt, find mass
why does using a colorimeter improve repeatability of results
quantitative so standardises the method
how does active site of an enzyme cause a high rate of reaction
lowers activation energy
induced fit causes active site to change shape
so ESC causes bonds to form/break
what bonds form between complementary base pairs
hydrogen bonds
name the 2 scientists who proposed models of the structure of DNA
Watson and Crick
what benefit does water have being cohesive
supports water columns in xylem of plants
provides surface tension for small organisms on ponds
