Biological Molecules Flashcards
Define monomer. Give some examples.
small repeating units that join together to form larger molecules
- monosaccharides (glucose, fructose, galactose)
- amino acids
- nucleotides
What happens in a condensation reaction?
joins monomers together and forms a
chemical bond, releasing water
What happens in a hydrolysis reaction?
breaks a chemical bond between
joined molecules and uses water
Name the three hexose monosaccharides.
glucose, fructose, galactose
Name the type of bond formed when monosaccharides react.
(1,4 or 1,6) glycosidic bond
Describe the structure of amylopectin (starch)
1,4 and 1,6 glycosidic bonds
Branched- many terminal ends for hydrolysis to break it down into glucose
Describe the structure of amylose (starch)
only 1,4 glycosidic bond
Helix/coiled with intermolecular H bonds
Describe the function of starch.
storage of alpha glucose in plants
-insoluble= doesn’t affect water potential
-large= doesn’t diffuse out of the cell
-compact- allows lots of glucose to be stored
Describe the structure and functions of glycogen.
Main storage polymer of 𝛼-glucose in animal cells
● 1,4 & 1,6 glycosidic bonds.
● Branched = many terminal ends for hydrolysis.
● Insoluble = no osmotic effect & does not diffuse out of cells.
● Compact.
Describe the structure and functions of cellulose.
polymer of 𝛽-glucose gives rigidity to plant cell walls
● 1,4 glycosidic bonds
● straight-chain, unbranched molecule
● H-bond crosslinks between parallel strands form microfibrils = high tensile strength
Benedict’s test for reducing sugars
- Add benedict’s reagent (blue) to sample
- Heat in a boiling water bath
- Positive = colour change from blue to orange & brick red precipitate (reducing sugar present)
Benedict’s test for non-reducing sugars
- Negative result as benedict’s remains blue
- Hydrolyse solution by adding HCl
- Heat in water bath for 5 minutes
- Neutralise with Sodium Carbonate Solution
- Proceed with Benedict’s test
How do triglycerides form?
Condensation reaction between 1 molecule of glycerol & 3 fatty acids forms ester bonds.
Entirely hydrophobic
Properties of saturated fatty acids
-solid at room temperature
-single covalent bonds only
- straight chain molecules
-mostly found in animal fats.
properties of unsaturated fatty acids
-have “kink” in the fatty acid chains
-liquid at room temp
- Found in plant cells
-Contain a C=C double bond
Relate the structure of triglycerides to their functions
High energy: mass ratioo= good energy storage
Has an Insoluble hydrocarbon chain= no effect on water
Slow conductor of heat, making it a great Thermal insulator
Describe the structure and function of phospholipids.
- glycerol backbone
- Attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head
- Forms phospholipid bilayer in water ( a component of membranes)
-Tails can splay outwards= waterproofing
Similarities between triglycerides and phospholipids
- Both have glycerol backbone
-Both formed by condensation reactions
- Both contain C, H and O
Are phospholipids and triglycerides polymers?
No; they are not made from a small repeating unit. They are macromolecules.
Why is water a polar molecule?
water has positively charged hydrogen atoms and negatively charged oxygen atoms
What are inorganic ions and where are they found in the body?
-Ions that don’t contain carbon atoms
- Found in the cytoplasm and extracellular fluid
Explain the role of hydrogen ions in the body.
lower the pH of solutions and impact enzyme and haemoglobin function
Explain the roles of iron ions in the body
A component of haemoglobin in the transport of oxygen
Explain the role of sodium ions in the body.
Involved in co-transport for absorption of glucose & amino acids
Explain the role of phosphate ions in the body
Component of:
- DNA (forms phosphodiester bonds with deoxyribose)
- ATP (makes ADP more reactive)
State the role of DNA in living cells.
Base sequence of genes codes for functional RNA & amino acid sequence of polypeptides.
Genetic information determines inherited characteristics = influences structure & function of organisms.
State the role of RNA in living cells.
to transfer the genetic code from DNA in the nucleus to the ribosomes.
Which bases are purines?
Adenine and Guanine
Which bases are pyrimidines?
cytosine, thymine, uracil
Name the complementary base pairs on DNA
2 H-bonds between adenine + thymine
3 H-bonds between guanine + cytosine
Name the complementary base pairs in RNA
2 H-bonds between adenine + uracil
3 H-bonds between guanine + cytosine
Relate the structure of DNA to its functions
- sugar-phosphate backbone & many H-bonds provide stability
- long molecule stores lots of information
- helix is compact for storage in nucleus
- base sequence of triplets codes for amino acids
- double-stranded for semi-conservative replication
- complementary base pairing for accurate replication
- weak H-bonds break so strands separate for replication
Describe the structure of messenger RNA
- short polynucleotide strand
- Contains uracil instead of thymine.
- Single-stranded & linear (no complementary base pairing).
Why is DNA replication called semi-conservative?
-Strands from original DNA molecule act as templates.
- New DNA molecule contains 1 old strand & 1 new strand
Outline the process of semi conservative replication
- DNA Helicase breaks H-bonds between base pairs
- Each strand acts a template
- Free nucleotides form nuclear sap attach to exposed bases via complementary base pairing
- DNA Polymerase catalyses condensation reactions attaches to adjacent nucleotides on new strand
- H Bonds reform
- Sugar phosphate backbone reforms
Describe the Messelson-Stahl Experiment
- Bacteria were grown in a medium containing heavy 15N for many generations
- Some bacteria were moved to a medium containing a light isotope of 14N. Samples were extracted after 1&2 cycles of DNA Replication
- Centrifugation formed a pellet. Heavier DNA settled closer to bottom of tube
Explain the role of ATP in cells.
ATP hydrolase catalyses ATP → ADP + Pi
- Energy released is coupled to metabolic reactions.
- Phosphate group phosphorylates compounds to make them more reactive.
How is ATP resynthesised in cells?
- ATP synthase catalyses condensation reaction between ADP & Pi
- during photosynthesis & respiration
Explain why ATP is suitable as the ‘energy currency’ of cells.
- High energy bonds between phosphate groups.
- Small amounts of energy at a time= less energy wasted
- Single step hydrolysis= energy avaliable
-Readily resynthesised
How many amino acids are there? and how do they differ?
20
differ only by R group
How do dipeptides and polypeptides form?
- Condensation reaction forms peptide bond (-CO and NH-) & eliminates molecule of water
● Dipeptide: 2 amino acids
● Polypeptide: 3 or more amino acids
Define primary structure
the order of the amino acids in a protein as determined by DNA
Define secondary structure
The twisting of a polypeptide into either an alpha helix or beta-pleated sheets due to hydrogen bonding between the amino acids
Define tertiary structure
further folding of the secondary structure to form a unique 3D shape. Disulphide bridges, Ionic bonds and Hydrogen bonds
Describe each type of bond in the tertiary structure of proteins.
-Disulfide bridges: strong covalent S-S bonds
-Ionic bonds: relatively strong bonds between charged R groups
-Hydrogen bonds: numerous and easily broken
Define quaternary structure
- Functional proteins that may consist of more than one polypeptide
-Precise 3D Structure held together by same bonds in tertiary structure
- May involve addition of prosthetic groups e.g. metal ions
Explain the induced fit model of enzyme action.
- Shape of active site is not directly complementary to substrate & is flexible.
- Conformational change enables ES complexes to form.
- This puts strain on substrate bonds, lowering activation energy.
How have models of enzyme action changed?
- Initially lock & key model: rigid shape of active site complementary to only 1 substrate.
- Currently induced fit model: also explains why binding at allosteric sites can change shape of active site.
Name 5 factors that affect the rate of enzyme-controlled reactions.
- enzyme concentration
- substrate concentration
- concentration of inhibitors
-pH
-temperature
How does substrate concentration affect the rate of reaction?
Given that enzyme concentration is fixed, rate increases proportionally to substrate concentration
Rate levels off when max number of E-S complexes form
How does enzyme concentration affect the rate of reaction?
Given that substrate is in excess, rate increases proportionally to enzyme concentration
Rate levels off when max number of E-S complexes form
How does temperature affect the rate of reaction?
Rate increases as kinetic energy increases & peaks at optimum temperature.
Above optimum, ionic & H-bonds in tertiary(3°) structure break = active site no longer complementary to substrate (denaturation).
How does pH affect rate of reaction?
Enzymes have a narrow optimum pH range.
Too high or too low of a pH interferes with amino acid charges causing bonds in the tertiary structure to break
What are the properties of competitive inhibitors?
-similar shape to substrate
- binds to active site
-prevents E-S complexes
- adding more substrates will knock out inhibitor resuming E-S complex formation
What are the properties of non-competitive inhibitors?
- binds to the allosteric site
- causes active site to change shape
- no more E-S complexes regardless how much more substrate is added
what is phosphorylation?
the process of ATP transferring energy to other compounds through the inorganic phosphate released during hydrolysis binding to different compounds making them reactive.
what are the 5 properties of water
metabolite - in condensation and hydrolysis reactions
important solvent in reactions- can dissolve and easily transport solutes in cytoplasm or plasma
a high specific heat capacity- buffers temperature
a large latent heat of vaporisation- provides a cooling effect with loss of water through evaporation (e.g. transpiration)
strong cohesion between water molecules- due yo hydrogen bonds between water molecules supports water columns(e.g. moving up xylem ) and provides surface tension
