TOPIC 1B-MORE BIOLOGICAL MOLECULES

Question 1

A) Describe “DNA”

Answer 1

A)-(deoxyribonucleic acid) used to store genetic info

–>all instructions organism needs to grow + develop from fertilised egg to fully grown adult.

Question 2

B) Descibe “RNA” and it’s function

Answer 2

B)-(ribonucleic acid) similar to DNA

• one main function is to transfer genetic info from DNA to ribosomes (body’s protein factories
• ->read the RNA to make polypeptides (proteins) in process called translation
• ribosomes themselves made from RNA + proteins.

Question 3

A) What are DNA and RNA polymers of?

B) Outline what a nucleotide is, its structure as well as it’s importance

Answer 3

A)-of nucleotides
B)-its a type of biological molecules
-composition: pentose sugat (sugar with 5 C atoms)/ nitrognen-containing organic base/phosphate group
-they are really important–>for start they’re monomers that make up DNA/RNA.

Question 4

A) Briefly explain the basic structure of DNA nucleotide

Answer 4

A)-the pentose sugar in DNA nucleotide called deoxyribose

• each DNA nucleotide has same sugar + phosphate group–>base on each nucleotide can vary though
• there are 4 possible bases: Adenine (A)/Thymine (T)/Cytosine (C) + Guanine (G)

Question 5

B) What is the composition of a basic RNA nucleotide

Answer 5

B)-RNA contains nucleotides with a ribose sugar (not deoxyribose)

• like DNA, an RNA nucleotide also has phosphate group + 1/4 different bases
• in RNA Uracil (U) replaces Thymine (T) as a base.

Question 6

A) Define the term “polynucleotide”

B) Describe the formation of polynucleotides

C) What is the “sugar-phosphate backbone”?

Answer 6

A)-polymer of nucleotides–>both DNA + RNA nucleotides form polynucleotides
B)-nucleotides join via condensation reaction between phosphate group of one nucleotide + sugar of another
–>forms phosphodiester bond (consisting of phosphate group + 2 ester bonds)
C)-chain of sugars + phosphates.

Question 7

DOUBLE HELIX DNA STRUCTURE:

A) Outline what the Double-helix structure is and how it forms

B) Describe complementary base pairing and what it results in

Answer 7

A)-DNA made of 2 polynucleotide strands/chains in double helix structure which join together via hydrogen bonding between the bases
-2 antiparallel (run in opposite directions) polynucleotide strands twist to form DNA double-helix structure.
B)-each base can only join with one particular partner
-Adenine always pairs with Thymine (A-T: 2 H bonds) and Cytosine with Guanine (C-G: 3 H bonds)
–>means always equal amounts of adenine and thymine in a DNA molecule + equal amounts of cytosine + guanine

Question 8

A) When was DNA first observed and what did most scientists at that time?

B) By 1953 what did experiments show and what did Watson and Crick show?

Answer 8

A)-1800’s
-they doubted it could carry genetic code as it has relatively simple chemical composition
–>some argued genetic info must be carried by proteins which are more chemically varied.
B)-experiments showed DNA was carrier of genetic code
-this also year in which double-helix structure which helps DNA to carry out it’s function determined by Watson + Crick.

Question 9

A) Compare the chain of an RNA molecule with a DNA one

Answer 9

A)-its a relatively short polynucleotide chain

• RNA is made from single polynucleotide chain (not double one)
• ->its much shorter than most DNA polynucleotides.

Question 10

A) Briefly outline what “semi-conservative DNA replication”

B) What does this semi-conservative DNA replication result in?

Answer 10

A)-DNA copies itself before cell division so each new cell has full amount of DNA
-its semi-conservative as half of strands in each new DNA molecule are from original DNA molecule
B)-means there is genetic continuity between generations of cells
–>(i.e: cells produced via cell division inherit genes from their parents).

Question 11

Outline and explain the steps in DNA replication:

A) Breaking down of the original strand

B) Complementary base pairing

Answer 11

A)-enzyme DNA helicase breaks hydrogen bonds between bases on 2 polynucleotide DNA strands
–>makes the helix unwind to form 2 single strands.
B)-each original strand acts as template for new strand
–>complementary base pairing means free-floating DNA nucleotides attracted to their complementary exposed bases (A + T and C + G)

Question 12

C) Joining up of the 2 new strands

D) What is the final result of DNA replication?

Answer 12

C)-condensation reactions join nucleotides of the new strand together–>catalysed by enzyme DNA polymerase
–>hydrogen bonds form between the bases on original strand + new strand
D)-each new DNA molecule contain 1 strand from original DNA molecule and one new strand.

Question 13

A) How are the end of DNA strands different?

Answer 13

A)-each end different in structure

• one end called 3’ (“three prime”) and other end 5’ ( “five prime”)
• in DNA helix–>strands run in opposite directions-antiparallel.

Question 14

B) What is significant about the active site of DNA polymerase in terms of the different ends of the DNA strands?

C) Consequently, what does this mean about the direction that the DNA strand is made?

Answer 14

A)-the active site only complementary to 3’ end of newly forming DNA strand–>so enzyme only able to be added to new strand at 3’ end
C)-means new strand made 5’ to 3’ direction + DNA polymerase moves down template in 3’ to 5’ direction
-as the strands in the double-helix are antiparallel–> the DNA polymerase working on one of the template strand moves in opposite direction to DNA polymerase working on other template strand.

Question 15

A) Give a brief background to the “Meselson and Stahl” experiment

Answer 15

A)-Watson + Crick determined DNA structure BUT also came up with semi-conservative DNA replication theory

• wasn’t confirmed until Meselson + Stahl’s experiment validated the theory
• ->before that people unsure if DNA replication semi-conservative OR conservative
• if method conservative–>original DNA strands would stay together and new DNA molecules would contain 2 new strands.

Question 16

B) How did Meselson and Stahl show that DNA is replicated via the semi-conservative method?

Answer 16

B)-their experiment used 2 isotopes of Nitrogen (DNA contains nitrogen)
–>heavy nitrogen (15N) and light nitrogen (14N)

Question 17

How did the experiment work?:

A) Initial growth of bacteria

B) First time spun in centrifuge

Answer 17

A)-2 samples of bacteria grown–>one in nutrient broth with light nitrogen + 1 with heavy nitrogen
-as bacteria reproduced–>took nitrogen up from broth to help make nucleotides for new DNA
–>so nitrogen gradually became part of bacteria’s DNA.
B)-DNA sample taken from each bacteria batch–>spun in centrifuge
–>DNA from heavy nitrogen bacteria settled lower down centrifuge tube than DNA from light nitrogen bacteria-as heavier.

Question 18

C) The mixing of the heavy and light nitrogen

Answer 18

C)-bacteria grown in heavy nitrogen broth taken out and put in broth containing only light nitrogen
–>bacteria left for 1 round of DNA replication–>then another DNA sample taken out and spun in centrifuge

Question 19

D) If DNA replication was conservative what results would you expect?

E) What results would you expect if DNA replication was semi-conservative?

F) As, it turned out what results did the experiment show?

Answer 19

D)-original heavy DNA which would still be together–> would settle at bottom and light DNA settle at top.
E)-new bacterial DNA molecules would contain 1 strand of old DNA containing heavy nitrogen + 1 new strand of DNA containing light nitrogen
–>so DNA would settle out between where light nitrogen DNA settled out and heavy nitrogen DNA settled out.
F)-DNA settled out in middle showing that the DNA molecules contained mix of heavy + light nitrogen
-bacterial DNA had replicated semi-conservatively in light nitrogen.

Question 20

G) How were the results of the Meselson and Stahl experiment used by other scientists?

Answer 20

G)-they had confirmed DNA replication in bacteria was semi-conservative
–>other scientists carried out experiments to show it was universal method for DNA replication in all living things.

Question 21

A) How much of the body does water make up?

B) Briefly outline the following important functions inside and outside of cells:

1-metabolite
2-solvent
3-temperature control
4-cohesion

Answer 21

A)-about 80% of cell’s contents
B)1-is metabolite in loads of important metabolic reactions including condensation + hydrolysis reactions
2-solvent–>means some substances dissolve in it
–>most metabolic reactions occur in solution (e.g: in cytoplasm of eukaryotic + prokaryotic cells) so water essential
3-helps with temp control as has high latent heat of vaporisation + high specific heat capacity
4-water molecules pretty cohesive (stick together)–> helps water transport in plants + transport in other organisms.

Question 22

A) What is the basic structure of water a moelecule?

B) Explain why water is a polar molecule

Answer 22

A)-H20 is one atom of oxygen (O) joined to 2 atoms of hydrogen (H2) via shared electrons
B)-as shared (-) hydrogen electrons pulled towards oxygen atom–>other side of each hydrogen atom left with slight (+) charge
–>unshared (-) electrons on oxygen atom give it slight (-) charge
–>makes water polar molecule–>has partial (-) charge on one side and partial (+) charge on other.

Question 23

C) How does hydrogen bonding arise between water molecules and what does that mean?

Answer 23

C)-slightly (-) charged oxygen atoms attract slightly (+) charged hydrogen atoms of other water molecules
–>this attraction is called hydrogen bonding and gived water some of it’s useful properties.

Question 24

A) Why is water an important metabolite?

Answer 24

A)-many metabolic reactions involve condensation or hydrolysis reactions

• hydrolysis reaction needs a water molecule to break a bond
• condensation reaction releases water molecule as new bond formed
• e.g: amino acids joined to make polypeptides (proteins) via condensation reactions
• ->energy from ATP released through hydrolysis reactions

Question 25

B) How does water having a HIGH LATENT HEAT OF VAPORISATION make it useful?

Answer 25

B)-takes lots energy (heat) to break hydrogen bonds between water molecules

• ->so water’s latent heat of vaporisation high-lots of energy used up when water evaporates (vaporises)
• ->this useful for living organisms as means they can use water loss via evaporation to cool down e.g: humans sweat to cool down) without losing much water

Question 26

C) Water is able to buffer (resist) changes in temperature. Why is this a useful property of water?

Answer 26

C)-H bonds between water molecules can absorb lots of the energy

• ->so water’s specific heat capacity high–>takes lots energy to heat it up
• ->useful for living organisms as means water not experience rapid temp change
• ->makes water good habitat as the temp under water likely to be more stable than on land
• ->water inside organisms also remains fairly stable temp–>helping them to maintain constant internal body temp.

Question 27

A) Explain how water’s polarity makes them a useful solvent

Answer 27

A)-lots of important substances in metabolic reactions are ionic (like salt)–>means they made from 1 (+) charged atom or molecule and 1 (-) charged atom/molecule

• ->e.g: salt-made from 1+ Na ion and 1- Cl ion
• as water polar–> + end of it will be attracted to - ion and - end of water molecule will be attracted to + ion
• ->means ions will get totally surrounded by water molecules–>DISSOLVE

Question 28

B) There is strong cohesion between water molecules. How is this a useful property of water?

Answer 28

B)-COHESION: attraction between molecules of same type (e.g: 2 water molecules)

• water molecules v. cohesive (tend to stick together) as polar
• strong cohesion helps water flow–>making good for transporting substances (e.g: its how water travels in columns up xylem (tube-like transport cells) in plants
• strong cohesion also means water has high surface tension when comes in to contact with air
• ->this is reason why sweat forms droplets which evaporate from skin to cool organism down
• ->also reason pond skaters + other insects can “walk on water”.

Question 29

A) Define respiration

B) Outline the structure of ATP (adenine triphosphate)

Answer 29

A)-the process of plant + animal cells releasing energy from glucose
B)-its made from nucleotide base adenine, combined with a ribose sugar + 3 phosphate groups
–>it’s what’s known as nucleotide derivative as its a modified form of a nucleotide.

Question 30

C) Explain the involvement of ATP in a cell obtaining energy from respiration

Answer 30

C)-a cell can’t get get it’s energy directly from glucose

• ->so in respiration energy released from glucose is used to make ATP
• once made ATP diffuses to part of cell where energy needed
• energy in ATP stored in high energy bonds between the phosphate groups
• ->its released via hydrolysis reactions.

Question 31

A) Describe what happens to the ATP molecule when energy is needed by a cell

Answer 31

A)-its broken down in to ADP (adenosine diphosphate) + Pi (inorganic phosphate)

• ->this is hydrolysis reaction as a phosphate bond is broken and energy is released
• ->the reaction is catalysed by enzyme ATP hydrolase

Question 32

B) Outline what it means to “couple” this ATP hydrolysis reaction

C)How may the inorganic phosphate also released be put to use?

D) Briefly explain the re-synthesis of ATP

Answer 32

B)-reaction can be “coupled” to other energy-requiring reactions in cell–>means energy released can be used directly to make coupled reaction occur than be lost as heat
C)-it can be added to another compound (phsphorylation) which often makes compound more reactive
C)-can be re-synthesised via condensation reaction between ADP and Pi
–>this occurs both in respiration + photosynthesis
–>and is catalysed by enzyme ATP synthase.

Question 33

Define the following terms:

A)Ion
B)Cation
C)Anion
D)Inorganic ion

E)Where are inorganic ions found and how does their role determine its conc?

Answer 33

A)-atom (or group of atoms) with electric charge
B)-ion with (+) charge
C)-ion with (-) charge
D)-ion which doesn’t contain carbon (but few exceptions)
E)-in solution/in cytoplasm of cells + in body fluids of organisms
-each ion has specific role depending on it’s properties
-an ions role determines whether it’s found in high/low concentrations.

Question 34

A) How are Iron ions an important part of haemoglobin?

Answer 34

A)-haemoglobin is large oxygen carrying protein in red blood cells

• its made of 4 different polypeptide chains each with an iron ion Fe2+ in centre
• it’s the Fe2+ that binds to O2 in hameoglobin-so is key component
• when O2 bound–>Fe2+ ion temporarily becomes Fe3+ ion until O2 released.

Question 35

B) Explain the importance of H+ ions in determining pH

C) How do Sodium ions (Na+) help transport glucose + amino acids across membranes

Answer 35

B)-pH calculated based on conc of hydrogen ions (H+) in environment
–>more H+ ions present the lower the pH (more acidic environment)
-enzyme-controlled reactions all affected by pH
C)-glucose + amino acids need help crossing cell membranes
-a glucose molecule/amino acid can be transported in to a cell (across cell surface membrane) alongside sodium ions (Na+)–>co-transport.

Question 36

D) Why are phosphate ions an essential component of ATP and DNA

Answer 36

D)-when phosphate ion (PO4 3-) attached to another molecule its known as a phosphate group

• DNA/RNA + ATP all contain phosphate groups
• its bonds between phosphate groups that store energy in ATP
• the phosphate groups in DNA + RNA let nucleotides join up to form the polynucleotides.