Biological molecules 3

Question 1

What is the structure of DNA?

Answer 1

• double stranded helix structure containing a sugar phosphate backbone with nitrogen contaning base pairs in the centre
• the base pairs contain the genetic code
• the back bone protects the base pairs from reacting with the environment

Question 2

What is a strand of DNA/RNA made up of?

Answer 2

• many joined nucleotides.

Question 3

What is the structure of a nucleotide?

Answer 3

• a phosphate group
• a pentose sugar
• an organic/nitrogenous base.

Question 4

What are the differences between DNA and RNA?

Answer 4

• In a DNA molecule the organic bases can either be Adednine , thymine ,cytoseine,guanine but in RNA thymine is replaced by uracil.
• In RNA the pentose sugar is Ribose rather than the deoxyribose found in DNA
• RNA is a much shorter strand than DNA
• RNA has no OH group on carbon 2
• RNA is half a strand

Question 5

How is the DNA polynucleotide formed?

Answer 5

• hydrogen bonds occur between the bases of opposite nucleotides
• Phosphodiester bonds occur between adjacent nucleotides.

Question 6

What bases bond with the other?

Answer 6

• the base pairing is specific
• adenine binds to thymine (uracil in RNA)
• cytoseine binds to guanine
• the bases are complimentary to eachother

Question 7

What is the 5’ side of the polynucleotide?

Answer 7

• the top of the polynucleotide molecule (on the right)
• this could also be the bottom of the molecule as the second half of the stand is inverted so the 5’ side could also be the bottom left of the strand

Question 8

What is the 3’ side of the polynucleotide?

Answer 8

• the bottom of the polynucleotide (on the left)
• also the top of the molecule on the right as the second half of the strand is inverted.

Question 9

What are the features of polynucleotides and how do they aid function?

Answer 9

• hydrogen bonds provide tensile strength
• long molecule stores alot of information
• double helix structure makes dna compact
• individual weak bonds join base pairs , easily broken for DNA replication
• double stranded allows for replication from template starbds
• base sequence allows information to be stored and determines amino acid sequence
• base stacking makes DNA stable

Question 10

What is a Purine?

Answer 10

These are larger bases that contain Two carbon ring structures (A and G)

Question 11

What is a Pyrimidines

Answer 11

these are smaller bases that contain one carbon ring structure (T and C)

Question 12

What happens in complimentary base pairing?

Answer 12

1. adenine pairs with thymine via 2 hydrogen bonds
2. cytosine pairs with guanine via 3 hydrogen bonds
   A smaller pyrimidine base always binds to a larger purine base. This arrangement maintains a constant distance between the two sugar-phosphate backbones.

Question 13

How is DNA adapted to its fuction?

Answer 13

• the sugar-phosphate/ phosphodiester backbone protects the more chemically reactive bases inside the double helix from reacting
• as there are more h bonds vetween cytoseine and guanine DNA molecules with a greater proportion of C-G pairings are more stable
• additional forces between base pairs hold up the molecules. (base stacking)

Question 14

Describe how DNA is replicated.

Answer 14

• stands of the double helix speprate and the Hydrogen bonds break
• with the help of DNA helicase
• Both strands act as templates for dna replication
• free nucleotides are attracted to the starnds
• and hydrogen bonds reform between base pairs
• complementary base pairing between AT and GC
• Dna polymerase joins nucleotides via phospjodiester bonds
• this is semi conservrative replication and produces 2 new strands.

Question 15

Describe what happens in the measelson and stahl experiment

Answer 15

1. they grew e-coli bacteria in an agar plate containing ‘heavy’ isotopes of nitrogen (15N) as its food. they then collected the bacteria ,homogenized, filtred and ran it through a centrifuge. a band of heavy (15N) DNA showed.
2. using the same agar plate they fed it ‘light’ 14 N agar. they then heated the e-coli to a temperatre of 56 degrees for 36 mins to allow for one division. they then collected this bacteria, homogenized, fitred and centrifuged it to produce a band of ‘hybrid 14-15 N DNA) towrads the top of the tube. (lighter contents are higher up in the tube)
3. allow 14-15 N bacteria to undergo one more cell division in an agar plate containig 14N agar. homogenize, filter centrifuge to produce two distinct band in the tube. the lighter band at the top containing 14-14N ‘light’ DNA and the band lower down containing 14- 15 N hybrid DNA

Question 16

Why was the measelson-stahl experiment so good?

Answer 16

• it disproved fully conservrative replication and the dispersive model and proved semi concervrative replication
• if fully conservrative replication occured, we would have one strand=of 14 N DNA and one of 15 N DNA after one division , but we had hybrid stands instead.

Question 17

What are the uses of energy?

Answer 17

• active transport. (co tansport in the ileum)
• muscle contraction for movement
• protein synthesis for growth and repair
• phosphorylation the attachment of a phosphate group to a molecule or an ion to lower the activation energy an make other molecules more reactive.

Question 18

Where is ATP produced?

Answer 18

• in the mitochondria via aerobic respiration
• Glucse + oxygen = carbon dioxide + water + ATP

Question 19

Where does the energy from respiration come from?

Answer 19

The energy from respiration takes the form of a nucleotide called adenosine triphosphate

Question 20

What is the structure of ATP?

Answer 20

• 3 phosphate groups
• bonded to a ribose sugar
• bonded to an adenine base

Question 21

How do we release energy from ATP?

Answer 21

• the bonds bwtween the outer most phosphate group in ATP are unstable so have a low activation energy
• A single hydrolysis reaction can remove a phosphate. the phosphate can from bonds with other molecules whic releases energy (Phosphorylation)

Question 22

What is the symbol equation for the Hydrolysis of ATP?

Answer 22

ATP + H2O = ADP (adesnosine diphosphate) + Pi (inorganic phosphate) + E (energy)

Question 23

What is the ATP -> ADP reaction catalysed by?

Answer 23

ATP hydrolase / ATPase

Question 24

How do you synthesise ATP?

Answer 24

The enzyme ATP synthase catalyses a condensation reaction to join a phosphate to ADP to form ATP
ADP + Pi + E = ATp + H2o

Question 25

What are the pros of ATP?

Answer 25

• releases energy iin small manageble amounts
• broken down in a one step reaction
• phorylates to lower the activation energy needed for bio mols to react
• rapidly reformed
• soluble, easier for reactions to take placein solution (cytoplasm)

Question 26

ATP vs Carbs / LIpids

Answer 26

1. atp small quantities while fats and glycogen is stored in large quanties in the cell
2. atp is rapidly reformed whole carbs lipids take longer to reform
3. energy from atp is released in small amounts while energy released in large soluble amounts
4. atp requires single hydrolysis to release while carbs / lipids require multiple reaction to be broken down
5. atp cannot be stored as it is too reactive glycogen/ fats are stored
6. atp is soluble . glucogen is insoluble

Question 27

Where does the energy needed to bind the phosphate to ADP come from?

Answer 27

• light (photophosphorylation)
• respiration
• Donor molecules

Question 28

How do you convert numbers into logarathims?

Answer 28

• log (number) = shrink number
• 10^x make number bigger again

Question 29

What is the equation for percentage difference?

Answer 29

percentage difference = differnce between values/ initial value x 100

Question 30

What is water and why do we describe it as a polar molecule?

Answer 30

• 2 hydrogen atoms covalently bonded to 1 oxygen atom.
• the electrons have an uneven distribution so water is a polar molecule
• where there are more electrons a delta negative region forms, the converse is true

Question 31

What is a hydrogen bond?

Answer 31

• a hydrogen bond is formed between polar molecules containg hydrogen.
• they do not result in a permanent structure, the bonds break and frm as water moves around.

Question 32

What are the properties of water?

Answer 32

• polarity acts as a good solvent (chemical reaction happen faster in solutions).
• reactive , can be used in hydrolysis reactions
• high specific heat capacity
• high latent heat of vaporisation
• cohesive
• adhesive
• trasparent
• variable desity

Question 33

why does a high specific heat capacity make water usefull?

Answer 33

• makes water a temperature buffer , enzymes are protected against temperature induced denaturing.

Question 34

Why does water have a high speific heat capacity?

Answer 34

• due to many hydrogen bonds that require alot of energy to overcome.

Question 35

why does a high latent heat of vaporisation make water usefull?

Answer 35

usefull for organisms who need sweat to cool them down.

Question 36

Why is water cohesive / adhesive?

Answer 36

hydrogen bonds cause water molecules to be attracted to eachother and other things.

Question 37

how is the cohesivness of water usefull?

Answer 37

• cohesion / adhesion of water in xylem
• allows for a continous column of water to move up in the xylem. (trasnpiration stream
• cohesion leads to surface tension, allows organisms to escape predators / find prey.

Question 38

Whaat ions are involved in biology?

Answer 38

• iron ions - FE2+ - involed in heamoglobin structure
• Phosphate ions - PO4-3 involved in phospholipids ATp, DNA , RNA
• Nitrate ions- No3- uptaken by plants make nitrogen containing biomols e.g amino acids
• Hydrogen bonds - H+ involvd in photsynthesis and respiration
• Calcium ions Ca2+ involved in muscle contraction
• Magnesium ions - Mg2+ involved in making chlorphyll.