Biological molecules pt 2

Question 1

DNA stands for and structure

Answer 1

Deoxyribose Nucleic Acid
Two strands twisted in a double helix structure with hydrogen bonds between complementary base pairs
Phosphate group, deoxyribose,nitrogenous base of adenine thymine cytosine guanine
Phosphate group has a negative charge
Covalent bonds
C1 of deoxyribose to nitrogenous base

Question 2

Monomer to polymer of nucleotides

Answer 2

Nucleotides form phosphodiester bonds in condensation reactions and are broken thriugh hydrolysis

Question 3

DNA VS RNA formula and relate to stability

Answer 3

C5O4H10 is DNA loss of oxygen is more stable than C5O5H10

Question 4

DNA vs RNA differences

Answer 4

Two strands (antiparallel) vs one strand
Nucleus vs nucleus and cytoplasm 
Thymine vs uracil 
Replicates and stores in for vs converts to a format acceptable for protein synthesis 
One type vs three types

Question 5

How/why is dna stable

Answer 5

Phosphodiester backbone protests the bases inside the double helix which fairies the genetic code so is protected from outside chemical and physical forces
Bases on each strand are linked by hydrogen bonds forming bridges between the sugar phosphate backbone
Many hydrogen bonds are string together

Question 6

DNA function and properties

Answer 6

Very stable allowing it to pass from generation to generation without changing - rare mutations
Two strands that can be separated during replication and protein synthesis
Large so carry huge amounts of genetic info
Base sequence of a gene determines structure and function of protein

Question 7

Semi conservative replication

Answer 7

DNA helicase enzyme breaks the hydrogen bonds between the complementary base pairs leaving them exposed and individual strands can act as a template for the new strand to be formed. Free activated nucleotides with two extra phosphate groups (which helps lower the activation energy and increase the likelihood of a reaction) binds to the complementary base pairs. DNA polymerase enzyme catalysts the synthesis of phosphodiester bonds starting on the strand ending on 3’ hence in the 5’ to 3’ direction. The new molecule formed retains half of the original DNA and half of the new.

Question 8

2 features of DNA and explain how each one is important in semi conservative replication (2 marks)

Answer 8

Hydrogen bonds between complementary base pairs are important because DNA helicase needs to break them in order to separate the strands leaving the bases exposed, allowing each strand to act as a template. Complementary base pairing allows for accurate replication.

Question 9

Dispersive model of DNA

Answer 9

Two molecules with old and new DNA dispersed between the strands

Question 10

Watson and crick used other scientists results but pieced it all together

Answer 10

All DNA bases contain nitrogen 14…..when bacteria is grown in a medium they will absorb nitrogen from the medium and incorporate it into the new nucleotides and ultimately DNA. All bacteria grown in a heavy medium then spun in a centrifuge which allows the heavy and light DNA to separate. Results showed only one line in the middle hence ruling out the conservative model. The second generation showed 14N and 15N line hence ruling out dispersive because that would only be one line.

Question 11

Why did many scientists not agree that nuclei acid contained the molecule of heritage

Answer 11

Proteins have 20 amino acids hence have numerous possibilities which seemed more suited to explain the genetic variation present in humans whereas there are only four nitrogenous bases.

Question 12

Explain why new nucleotides can only be added in the 5’ to 3’ direction

Answer 12

The enzyme DNA polymerase is specific and has an active site of a complementary shape to the 3 OH group of 5’ strand and phosphate of growing strand hence can only work on substrate in that direction.

Question 13

ATP stands for and is an…with an extra… which makes it …..

Answer 13

Adenosinetriphosphate

Activated nucleotide - extra phosphate bond makes it more reactive so easily broken down

Question 14

Function of ATP

Answer 14

Stores chemical energy from glucose as chemical energy in ATP

Question 15

ATP hydrolysis

Answer 15

Energy stored in ATP is released (exothermic) by breaking off third phosphate and small amounts of energy are steadily related to drive energy requiring process in the cell.
ATP hydrolyse catalyses the hydrolysis

Question 16

ATP hydrolysis is exergonic meaning

Answer 16

Energy is released

Question 17

Condensation of ATP

Answer 17

Adds phosphate group, ATP synthase catalyses the synthesis and is endergonic hence energy is required.

Question 18

3 ways to make ATP

Answer 18

Phosphorylation in chloroplasts uses light energy in a condensation reaction
Oxidative phosphorylation uses glucose and other fuels in a condensation reaction
Substrate level phosphorylation is when the phosphate group is in a high energy bond with sugar substrate instead of dissolved in cytoplasm .
Base reaction is ADP plus Pi = ATP plus water with arrows for light or fuels upwards
Last reaction is sugar substrate plus ADP gives sugar substrate plus ATP

Question 19

Functions ATP examples

Answer 19

Anabolism so protein synthesis
Muscle contraction - needed for filaments to slide past one and other
Active transport
Secretion of substances from cells - needed to form lysosomes
Activation if Molecules - glycolysis - add phosphate toe glucose molecules so can be broken into TP

Question 20

Explain how the hydrolysis of ATP for energy requiring reactions (endergonic) is useful

Answer 20

ATP is an immediate source of energy for cells (better than glucose) and can be rapidly synthesised after hydrolysis and transfers small manageable amounts of energy for reactions that require it

Question 21

What are enzymes

Answer 21

Enzymes are globular proteins that act as biological catalysts that speed up a reaction by lowering the activation energy without getting used up.

Question 22

How is the function of enzyme reliant on its primary protein structure?

Answer 22

The primary protein structure is the sequence of amino acids that then fold in on each other forming a 3D molecule. An enzyme has a specific shape that will fit the substrate the enzyme is meant to work upon. A change to the primary structure would cause a difference in bonds formed during folding hence changing the shape rendering the active site useless and unable to form an enzyme - substrate complex.

Question 23

What is the induced fit model of action?

Answer 23

Proposes that the decreased proximity of substrate is a change in the environment of the enzyme causes the shape of the enzyme to change , like a glove does to a hand, to accommodate the substrate. As the enzyme changes shape, strain is applied on the substrate molecule which distorts the bonds in the substrate, consequently lowering the activation energy.

Question 24

Locke and Key model limitations

Answer 24

Older model than induced fit
Too rigid as enzymes are extremely specific hence does not explain scientists observing enzymes accommodating similarly shaped molecules to that of the intended substrate.

Question 25

Describe and explain how temperature affects the rate of reaction (describe the graph).

Answer 25

Like a bell (rate on y optimum temp on x)
Rise in temperatures increases the kinetic energy of the molecules hence they move more rapidly which increases the frequency of successful collisions so more enzyme - substrate complexes are formed hence the rate of reaction increases. However too high temperatures cause denaturisation if enzyme, hence the rate of reaction slows down in human enzymes at around 45 degrees Celsius and becomes denatured at around 60 degrees C.

Question 26

Birds have a ——- metabolic rate than humans because

Answer 26

Higher

For flight hence higher body temp

Question 27

What is pH a measure of

Answer 27

Hydrogen concentration

Question 28

Describe the graph of rate of reaction and pH and explain

Answer 28

Change in pH alters the charges of amino acids that make up an active site hence the substrate can’t form bonds to the enzyme.
Significant change in pH may cause bonds maintains the enzymes tertiary structure to break - more likely to reduce enzyme efficiency then denature.
Active site arrangement consists of hydrogen and ionic bonds between NH2 and COOH groups
Steep up and slow down a bit like a mountain.

Question 29

Enzyme concentration and rate of reaction graph description and explanation

Answer 29

Enzyme concentration increasing will increase rate of reaction as long as there is an excess of substrate however if the substrate is limiting then no effect on rate of reaction.
Gentle rise then plateaus

Question 30

Describe and explain the graph of substrate concentration and rate of reaction

Answer 30

Rate of reaction increases in proportion to the concentration of substrate until all enzymes are working at maximum speed then no effect p.
Gentle rise and plateau.

Question 31

Competitive Inhibitors do what

Answer 31

Occupy the active site of an enzyme made for a different substrate

Question 32

Non competitive inhibitors do what

Answer 32

Bind on an allosteric not active site) changin shape of molecule

Question 33

Compare rate of reaction with competitive and non competitive inhibitors

Answer 33

Non competitive is a much more gentle slope and plateaus more quickly whilst competitive albeit slowly eventually reaches the plateau point for the intended substrate.

Question 34

Inhibitors can be useful

Answer 34

Negative feedback loops inhibit starting product so that any increase in concentration is automatically regulated by the body.

Question 35

Why is a dna molecule with more CG bases more stronger than AT?

Answer 35

CG has three hydrogen bonds AT has two so harder to break CG

Question 36

Why is helix structure useful for function of DNA?

Answer 36

Helix is compact for storage of genetic info in nucleus

Question 37

Relate the structure of mRNA to its functions

Answer 37

Breaks down quickly so no excess polypeptide forms
Ribosome can move along strand and tRNA can bind to exposed bases
Can be translated into a specific polypeptide by ribosomes.

Question 38

Explain why ATP is a suitable energy source foer cellprocesses

Answer 38

High energy bonds between phosphate groups
Small amounts of energy released at a time means less energy wasted as heat
Single step hydrolysis means energy is available quickly
Readily re-synthesised.

Question 39

Describe specificity of enzymes

Answer 39

Active site of a complementary tertiary structure to its substrate, allowing for enzyme substrate complexes to be formed. If not complementary then binding between will not occur properly and no catalysis will occur

Question 40

RNA structure

Answer 40

Ribose sugar, phosphate group and Adenine,guanine,cytosine and uracil
Linear strand phosphodiester bonds
RELATIVELY SHORT

Question 41

Structure of ATP and state two differences to dna nucleotide

Answer 41

Adenine bonded to ribose which is bonded to one phosphate which is bonded to two other phosphates in a line

One phosphate vs three phosphates
Deoxyribose vs ribose

Question 42

Why is ATP useful in many biological processes? (5 marks)

Answer 42

Releases small amounts of manageable energy
Broken down in a one step process
Provides energy immediately
Hydrolysis provides phosphates which make a compound more reactive, lowering Ea which is useful for enzyme controlled reactions
Reformed after hydrolysis

Question 43

Enzymes intracellular and extracellular reactions

Answer 43

ATP

Digestion