12.3 - Nucleic acids, ATP, water + Inorganic ions

Question 1

What does DNA and RNA stand for and what are they?

What does DNA do?

What does RNA do?

What monomers are the polymers DNA and RNA made of?

Answer 1

Deoxyribonucleic acid.
Ribonucleic acid.
They are nucleic acids and are important information carrying molecules.

DNA holds genetic information.

RNA transfers genetic information from DNA to the ribosomes.

Nucleotides.

Question 2

What is the structure of a DNA nucleotide?

What is the structure of a RNA nucleotide?

Answer 2

Composes of a DEOXYRIBOSE sugar, a PHOSPHATE group and a nitrogen-containing BASE (either Adenine, Cytosine, Guanine or Thymine.)

Composes of a RIBOSE sugar, a PHOSPHATE group and a nitrogen-containing BASE (either Adenine, Cytosine, Guanine or Uracil.)

Question 3

Describe how a phosphodiester bond is formed between two nucleotides in a DNA molecule. (3)

Answer 3

1) Condensation reaction (loss/removal of water)
2) Between phosphate and deoxyribose (3rd carbon)
3) Catalysed by DNA polymerase.

Question 4

Describe the structure of DNA (5)

Answer 4

1) Polymer of nucleotides
2) Each nucleotide is formed from deoxyribose, a phosphate group and a nitrogenous base
3) Phosphodiester bonds between nucleotides
4) Double helix / 2 strands held by weak hydrogen bonds
5) Hydrogen bonding between A + T, C + G.

Question 5

How many H-bonds are formed between the complementary base pairs Adenine and Thymine?

How many H-bonds are formed between the complementary base pairs Cytosine and Guanine?

Answer 5

Two. (T for two)

Three. (C rhymes with 3)

Question 6

To make sure the two strands remain parallel, A pairs with T and C with G, also both strands of DNA run in…

Each end of the molecule has a..

Why is this important?

Answer 6

…opposite directions, meaning they are antiparallel. Parallel but oppositely oriented.

…5’ end and a 3’ end, = which Carbon is involved with the phosphodiester bond.

This is important when making proteins, so only one strand is read. Also in DNA replication as DNA polymerase only has a complementary A.S to the 5’ end (P group) of the molecule.

Question 7

Describe how the structure of DNA relates to its function. (8)

Backbone…
Helix…
Base pairs…
Bonding…

Answer 7

1) Sugar-phosphate backbone and double-helix = provides strength and stability by protecting bases and H-bonds.

2) Long/large molecule so can store lots of information.

3) Helix / coiled so compact

4) Base sequence allows information to be stored as it codes for AAs/proteins

5) Double stranded so DNA replication can occur semi-conservatively / one strand = template

6) Complementary base pairing so accurate copies can be made.

7) Weak Hydrogen bonding for easy strand separation in DNA replication

8) Many weak hydrogen bonds so strong/stable molecule.

Question 8

Why must DNA be copied at cell division?

What does “semi conservative” DNA replication mean?

Why is semi-conservative DNA replication important?

Answer 8

So that each of the new daughter cells receives a copy of the DNA.

In a new molecule of DNA, half the molecule is old as it is conserved and half is new.

To ensure genetic information stays the same between generations of cells.

Question 9

What enzymes are involved in semi-conservative DNA replication and what are their functions?

Answer 9

DNA polymerase - catalyses the condensation reactions between DNA nucleotides to form the sugar-phosphate backbone of the new strand.

DNA helicase - breaks (NOT HYDROLYSE) the hydrogen bonds between complementary base pairs so that each strand can act as a template,

Question 10

Describe semi-conservative DNA replication (7)

Answer 10

1) DNA helicase breaks the hydrogen bonds between complementary base pairs
2) Strands separate
3) Both strands act as a template
4) Free nucleotides are attracted and attach to exposed bases
5) Complementary base pairing due to H-bonds forming between bases
6) DNA polymerase joins adjacent nucleotides together on the new strand forming phosphodiester bonds through condensation reactions.
7) The new DNA molecule contains an original strand and a new strand.

Question 11

Name the two scientists who proposed models of the chemical structure of DNA and DNA replication.

What experiment proved the W + C model of DNA replication?

Answer 11

Watson and Crick.

The Meselson Stahl experiment - proved that DNA is replicated semi-conservatively and NOT conservatively or dispersively.

Question 12

Describe how the separation of strands occurs. (2)

Answer 12

1) DNA helicase
2) Breaks Hydrogen bonds between complementary base pairs

Question 13

Describe the role of DNA polymerase in the semi-conservative replication of DNA. (3)

Answer 13

1) Joins adjacent DNA nucleotides
2) Catalyses condensation reactions
3) Catalyses formation of phosphodiester bonds

Question 14

Give two features of DNA and explain how each one is important in the semi conservative replication of DNA (3)

Answer 14

1) Weak / easily broken H bonds between bases allow two strands to separate
2) Two strands, so both can act as templates
3) Complementary base pairing allows accurate replication.

Question 15

State five structural differences between a DNA molecule and a mRNA molecule. (5)

Answer 15

1) DNA has deoxyribose, mRNA has ribose.
2) DNA has thymine, mRNA has uracil
3) DNA longer, mRNA shorter
4) DNA double stranded, mRNA single stranded
5) DNA has hydrogen bonds, mRNA = no hydrogen bonds

Question 16

What does ATP stand for?

What is it?

What is it formed of?

Answer 16

Adenosine Triphosphate

A nucleotide derivative

Formed of a RIBOSE sugar, an ADENINE base and 3 PHOSPHATE groups.

Question 17

How is ATP formed to create a high-energy bond?

From what constituent molecules and requires what?

Answer 17

It is formed from ADP (adenosine DIphosphate) and a phosphate group.

It requires energy to add a phosphate group to ADP to form ATP, so it creates a high energy bond between the 2nd and 3rd phosphate groups. This involves a condensation reaction and the enzyme ATP synthase.

Question 18

What does ATP hydrolyse into?

What happens between the 2nd and 3rd phosphate?

ATP is produced IN…

Answer 18

It is hydrolysed into ADP and Phosphate in a hydrolysis reaction, requiring a molecule of water and the enzyme ATP hydrolase.

The bond between the 2nd and 3rd phosphate breaks, releasing small manageable amounts of useable energy.

…respiration and photosynthesis.

       HYDROLYSIS
     ATP hydrolase

 ATP ---------------------> ADP + Pi
    <---------------------

ATP synthase
CONDENSATION

Question 19

ATP is used as an energy source in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use. (5)

Answer 19

1) Releases relatively small amount of energy
2) Releases energy instantaneously
3) Phosphorylates other compounds, making them more reactive
4) Can be rapidly re-synthesised
5) Doesn’t leave cells

Question 20

Describe how an enzyme can be phosphorylated (2)

Answer 20

1) Attachment of inorganic phosphate group to the enzyme
2) Released from the hydrolysis of ATP

Question 21

Water is a dipole molecule as it has an….

Oxygen has a d- charge because…

Answer 21

…unequal sharing of electrons

…oxygen has more protons (8) than hydrogen (1) so pulls the electrons closer to its nucleus, putting a slightly negative charge on the Oxygen atom, and a slightly positive charge on the hydrogens.

Question 22

Explain five properties that make water important for organisms. (6)

Answer 22

1) A metabolite (used and produced) in condensation/hydrolysis/respiration/photosynthesis
2) A solvent so metabolic reactions can occur
3) High specific heat capacity so buffers changes in temperature (resists temperature fluctuations - takes more energy to heat water than air)
4) Large latent heat of vaporisation so provides a cooling effect through evaporation (lots of energy needed to break H bonds in water, lowering temp of organism)
5) Cohesion between water molecules so supports columns of water in plants (xylem vessels)
6) Cohesion so produces surface tension supporting small organisms.

Question 23

Give two properties of water that are important in the cytoplasm of cells. Explain its importance. (6)

Answer 23

1) Polar molecule
2) Acts as a universal solvent
OR
1) Universal solvent
2) So metabolic reactions occur faster in solutions
OR
1) Reactive
2) Takes place in hydrolysis / condensation

Question 24

State and explain the property of water that helps to prevent temperature increase in a cell. (2)

Answer 24

High specific heat capacity

Buffers changes in temperature

Question 25

Suggest why water becomes lighter as it expands. (2)

Suggest one biological advantage of this property ^^ (3)

Answer 25

1) Density = mass/volume
2) Ice has same mass as water but greater volume

1) Ice is colder than water
2) Being lighter than water, ice floats on water
3) Reduces freezing of water below ice ( protects organisms )

Question 26

Describe the roles of iron ions, sodium ions and phosphate ions in cells.

Answer 26

/ IRON /
- haemoglobin associates with oxygen / transports O2

/ SODIUM /
- co-transport of glucose/AAs into cells
- As sodium moved out by active transport

/ PHOSPHATE /
- Joins adjacent nucleotides together in phosphodiester bonds in backbone of DNA / RNA
- Used to produce ATP
- Phosphorylates other compounds making them more reactive
-Hydrophilic part of phospholipid bilayer