3.1 Biological Molecules Flashcards
What are monomers? + e.g
Monomers are smaller units from which larger molecules form (polymers)
E.g monosaccharides, amino acids, nucleotides
What is a condensation reaction?
1) joins 2 molecules together
2) forms chemical bond
3) elimination of water molecule
What is a hydrolysis reaction?
1) breaks chemical bond
2) between 2 molecules
3) involves use of water molecules
What is a monosaccharides? + e.g
Monomers from which larger carbohydrates are made
E.g glucose, fructose and galactose
What is/forms when 2 monosaccharides join?
Condensation reaction which forms a glycosidic bond by removing H2O
What are the examples of disaccharides?
• 2 glucose= maltose + water
• glucose + fructose = sucrose + water
• glucose + galactose = lactose + water
What is the definition of isomers (e.g)?
Same molecular formula but different structure. Glucose has 2 isomers= alpha and beta glucose
How are polysaccharides formed? (E.g)
Condensation reaction of many glucose units
•Glycogen + starch = alpha glucose
•cellulose= beta glucose
Describe starch (polysaccharide)
1) store of glucose in plants
2)2 polymers=
•amylose-unbranched helix
•amylopectin-branched molecule
3) •helix-compact to fit +glucose in small space
•branched- +SA for rapid hydrolysis back to glucose
•insoluble-no affect water potential
Describe cellulose (polysaccharide)
1) structure strength for cell wall
2)•long straight chains
•chains held in parallel by +H2 bonds to form fibrils
3)• +H2 bonds- give collective strength
•insoluble- no affect water potential
Describe glycogen (polysaccharide)
1) store of glucose for animals
2) •highly branched molecule
•very compact: lots stored
3)•branched- +SA for rapid hydrolysis back to glucose
•insoluble-no affect water potential
What is the difference between the alpha and beta glucose isomers?
Hydroxyl group in c1 is in a different position
What are all monosaccharides and some disaccharides (e.g maltose)?
Reducing sugars except sucrose
How are reducing sugars tested? +results
1) liquid form or grind in test tube
2) add equal vol Benedict’s reagent
3) heat mix in gently boiling water bath for 5 mins
+ result= blue to red
Why does a reducing sugar turn Benedict’s solution into red?
Reduces the chemical (donates e-) which forms the Cu(II)SO4 into an insoluble red precipitate of Cu(I)O
How are triglycerides formed and what is their bond called?
3 Condensation reaction between 3 fatty acids and glycerol. Forming 3 ester bonds
What is the general formula of fatty acids and what can they be?
RCOOH
•saturated
•unsaturated
What are saturated fatty acids?
Only single bonds between Carbon atoms within HC chain
What are unsaturated fatty acids?
Have one or more double bonds between carbon atoms in HC chain
What is the structure and function of triglycerides?
•energy store: high ratio of energy storing C-H bonds
•metabolic water source: high ratio of H2:O2. Water forms when oxidised
•insoluble: no affect on water potential as large + hydrophobic
•low mass: lots stored, less mass
How are phospholipids made?
Condensation reaction between 2 fatty acids and glycerol. Forming 2 ester bonds
How are phospholipids different to triglycerides?
They have a negatively charged phosphate group (hydrophilic) instead of a 3rd fatty acid.
What happens when phospholipids are placed in water?
•polar Hydrophilic phosphate ‘head’ faces water (attracted). Hydrophobic fatty acid ‘tails’ so move inwards (repel).
•This forms a bilayer where centre acts as a barrier to water soluble substances.
What are cell membranes composed of?
Phospholipid bilayer
How is the emulsion test carried out?
1) shake lipids in ethanol = dissolved
2) add distilled water
3) white emulsion formed
How is starch tested for?
Add iodine solution to 2cm3 sample. Iodine in potassium iodide solution turns orange to blue-black
How do you test for non-reducing sugars?
•Benedict’s test: negative (blue)
•boil in HCl to hydrolyse to monosaccharides
•cool and neutralise with sodium hydrogen carbonate
•redo Benedict’s test = brick red
Why do you add Sodium hydrogen carbonate during non reducing sugar test?
As Benedict’s solution doesn’t work in acidic conditions
How can the quantity of reducing sugar in a solution be tested?
•colorimeter: light absorbance
•filter and dry to find weight
Why does using a colorimeter improve repeatability?
•quantitative
•standardised method
•colour change is subjective
How is a dipeptide and polypeptide chain formed? (+name of bond)
Di:condensation reaction between 2 amino acids
Poly: condensation reaction between many amino acids
Peptide bond
What is an amino acid composed of?
•Amino group (NH2)
•Carboxylic group (COOH)
•R group
What is the ‘R’ group in an amino acid?
Variable group for 20 different amino acids
How is a peptide bond formed between amino acids?
Condensation reaction between OH of Carboxylic group and H of amine group. Forming a molecule of H20
What is the primary structure of a protein and what will happen if it is changed?
1) sequence of amino acids joined by peptide bonds in a polypeptide chain
2) change in aa sequence causes bonds to form at different locations so change in 3D shape
What is the secondary structure of proteins?
Hydrogen bonds form between amino acids in the chain so coil to alpha helix or fold to a beta pleated sheets.
Where do hydrogen bonds form in the secondary structure of proteins?
Form between C=O groups of Carboxyl group and N-H in the amine group
What is the tertiary structure of proteins?
The chains are coiled and folded more, so more bonds form between different parts of polypeptide e.g ionic, hydrogen and disulphide bridges between the R groups
This forms the unique 3D shape
Where do ionic and disulphide bonds form between in the tertiary protein structure?
Between R groups
Where disulphide bonds: only 2 R’s with S
What is the quaternary structure of protein?
Several different polypeptide chains held by bonds to from unique 3D structure
What happens to the protein structure when they denature?
The bonds between the 2nd and 3rd structure will break and 3D shape is lost. No longer complementary
How is protein tested for?
Biuret test:
1) add drops of NaOH solution (alkali)
2) add Cu(II)SO4 solution
3) + test= blue to purple
What is a conjugated protein?
Proteins combined with non-protein substances (prosthetic groups)
What is a fibrous protein?
e.g collagen + keratin
•insoluble
•structural
What is a globular protein?
e.g enzymes + haemoglobin
•soluble
•3D shape
What is an enzyme?
Biological catalyst with a tertiary structure active site that is complementary to the substrate and will lower its activation energy
What is the lock and key theory?
Specific substrate bonds to a complementary active site, that has a fixed shape
What is the accepted model of the enzyme catalyst?
Induced fit model:
•active site will mould around the substrate (complementary)= enzyme substrate complex
•puts strain in the bonds, lowering activation energy
•returns to original shape + reused
How does temperature effect rate of reaction of an enzyme?
•below optimum: low KE so less successful collisions with substrate
•above optimum: denatures, active site changes shape so no more enzyme substrate complexes
How does ph effect rate of reaction of an enzyme?
Too low or too high Ph:
•interferes with charges in amino acids
•breaks (ionic) bonds holding tertiary structure, active site shape changes
•denatures = no more enzyme substrate complexes
Optimum:
Active site is most complimentary to substrate
What happens when an enzyme is denatured?
The bonds holding the tertiary structure will break which will change its unique and specific 3D shape. Changing active site’s complimentary shape so less E-S complexes
Why does a graph plateau when enzyme concentration continues to increase?
There are empty active sites but insufficient substrates to catalyse.
Why does a graph plateau when substrate concentration continues to increase?
Enzyme active sites are all saturated
How do competitive inhibitors affect enzyme reactions and what happens when you add more substrate?
•similar shape to substrate so will bind to active site, preventing enzyme substrate complexes
• more substrate= flood and out compete inhibits so they are knocked out of active site
How do non-competitive inhibitors affect enzyme-substrate reactions?
•binds to allosteric site, away from active site
•causes active site to change shape so it is no longer complementary to substrates
•less E-S complexes
What does DNA do?
•codes for sequence of ‘AA’ in primary protein structure and determines the final 3D structure and function
•holds genetic info
•polymer made up of nucleotides
What is a nucleotide made up of for DNA?
•Phosphate group
•pentose sugar: deoxyribose
•organic bases: adenine+thymine, cytosine+guanine
How is a polynucleotide and double helix in DNA formed?
polynucleotide: condensation reaction between nucleotides forming phosphodiester bonds = sugar phosphate backbone
double helix: 2 polynucleotides bind by H-bonds between complimentary base pairs. This coils and twists
How does the structure of DNA link to its function?
•stable + strong : sugar phosphate backbone with covalent bonds
•double stranded:replication using a strand as a template
•weak h-bonds: easy to unzip for replication
•long tightly coiled molecule: carries lots of info
•complimentary base pairing: allows identical copies to be made
•sequence of bases: allows info to be stored
•double helix: protects weak H-bonds, prevents damage to code
What is RNA and what is it composed of?
Short polynucleotide which transfers genetic info from DNA to ribosomes
•phosphate group
•ribose sugar
•uracil+adenine and cytosine+guanine
What is MRNA and why is it useful?
Messenger: carries the genetic code of one gene from nucleus to the ribosome
•much shorter than DNA so can leave nucleus
•short lived: broken down by the time it has carried out function
•single stranded, every 3 bases (codon)= AA
What is the function of TRNA?
•attaches to one of the 20 different AA and transfers this AA to ribosome = polypeptide chain
•specific AA attach to TRNA based on the complimentary codons on the MRNA = anticodon
What is Rrna?
Subunit of ribosomes
Protein+RRNA = ribosomes
Why is RNA different to DNA?
•much shorter
•single stranded
•contains uracil not thymine
•contains ribose not deoxyribose as pentose sugar
What is the process of semi conservative replication?
- DNA helicase breaks H-bonds between complimentary base pairs in polynucleotide strands= double helix unwinds
*each strand acts as a template - Free floating nucleotides are attracted to exposed base pairs on template strands and form H-bonds
- DNA polymerase joins the adjacent nucleotides together by condensation reaction, forming phosphodiester bonds
= 2 daughter DNA with parental strand and synthesised strand
How was semi conservative replication proved correct?
•bacteria grown in medium of nitrogen isotopes (14N light and 15N heavy)
•DNA spun in centrifuge and separated due to density (top:14 bottom:15)
•when 14N added to 15N DNA, centrifuge will show 100% 14N-15N in middle
What is ATP?
•Nucleotide derivative
•immediate source of energy
•ribose, adenine and 3 inorganic phosphate groups
How does ATP release energy?
Hydrolysis of ATP is catalysed by ATP hydrolase into ADP + Pi (+energy)
How is ATP made?
Made in respiration by a condensation reaction between ADP +Pi, catalysed by ATP synthase
What is phosphorylation?
When inorganic Pi released from the hydrolysis of ATP makes other compounds more reactive
Why is ATP more useful than glucose?
•small, manageable amounts of energy so less wasted = less heat
•both: small + soluble so easily transported around the cell
•only one bond hydrolysed so faster
•phosphorylation
•ATP can’t pass out of cell, so all cells have constant ATP supply
What is the structure and function of water that make it useful?
1) metabolite-metabolic reactions e.g hydrolysis
2)polar so universal solvent-transport of substances / reactions can occur
3)high heat capacity-buffers changes in temperature e.g for enzymes
4) large latent heat of vaporisation-cooling effect with little water lost by evaporation
5) strong cohesion between H20 molecules-continuous column of water (xylem) + surface tension= habitat
What are some important inorganic ions in the body?
•iron: Fe2+ in haemoglobin will bind + transport oxygen
•H+: maintain Ph, important for ATP synthase
•sodium: communication between neurones, co-transport of aa/glucose
•phosphate: groups in DNA, ATP and RNA, phosphorylation, hydrophilic phospholipid area, joins nucleotides
(Both Na and phosphate affect osmosis/ water potential)
What is end product inhibition and what happens when it is high/low?
•regulate metabolic pathways
High: binds non-competitively to enzyme, blocking more production
Low: inhibition ends and pathway restarts
Why is the direction in which new DNA strand made different for the 2 strands?
•DNA has anti parallel strands
•shape of nucleotides is different/aligned differently
•DNA polymerase have specific active sites
•only substrates with complementary shape bind
•only complementary with phosphate end of developing strand
Which bases are purines and which are pyramidines?
AG: purine
TCU: pyramidines
How can a colorimetry be used to give qualitative results for unknown samples?
1.make standard solutions of known conc. and record its % absorbance or transmission (a/t)
2.plot calibration curve: % a/t in y-axis and conc. in x-axis
3.find % a/t of unknown values and use graph to read off conc.
How is glucose well suited to its role?
•soluble so easily transported around organisms
•small molecule so it can diffuse across membrane
•broken down easily to release energy in the form of ATP
•join to form di and polysaccharides
