biological molecules - nucleic acids, water and ATP

Question 1

What do DNA and RNA stand for?

Answer 1

DNA - Deoxyribonucleic acid
RNA - Ribonucleic acid

Question 2

What is the role of DNA and RNA?

Answer 2

DNA holds genetic information
RNA transfers genetic information from the DNA to the ribosomes.

Question 3

What monomer is DNA made up from?

Answer 3

nucleotide

Question 4

What is a polymer of DNA called?

Answer 4

polynucleotide

Question 5

what components make a nucleotide?

Answer 5

a pentose, a phosphate group, and a nitrogenous base

Question 6

What is a DNA nucleotide made of?

Answer 6

deoxyribose, a phosphate group, and one of the organic bases adenine, thymine, guanine, or cytosine.

Question 7

what is an RNA nucleotide made of?

Answer 7

ribose, a phosphate group, and one of the organic bases adenine, uracil, guanine, or cytosine.

Question 8

What bond forms from the condensation of two nucleotides?

Answer 8

a phosphodiester bond

Question 9

What is the structure of a DNA molecule?

Answer 9

A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary
base pairs. The sugar and phosphate form a backbone which protects the bases.

Question 10

What is an RNA molecule?

Answer 10

a relatively short polynucleotide chain

Question 11

Explain the process of semi-conservative DNA replication

Answer 11

-DNA helicase breaks the hydrogen bonds between the complementary base pairs between the 2 strands of the double helix
-This causes the DNA double helix to unwind
-Each of the separated parental DNA strands act as a template
-Free floating DNA nucleotides within the nucleus are attracted to their complementary base pairs on the template strands of the parental DNA.
-The adjacent nucleotides are joined together to form the phosphodiester bond by a condensation reaction
-DNA polymerase catalyses the joining together of adjacent nucleotides
-The 2 strands of daughter DNA contain one strand of parental (original) DNA and one newly synthesised strand.

Question 12

What is the structure of water?

Answer 12

2 atoms of hydrogen covalently bonded to one molecule of oxygen. Molecule is charged and so attraction between 2 charges forms hydrogen bonds between water molecules

Question 13

What are the properties of water?

Answer 13

-relatively high specific heat capacity
-relatively large latent heat of vapourisation
-strong cohesion between water molecules
-an important solvent
-a metabolite in many metabolic reactions

Question 14

Explain the high heat capacity of water

Answer 14

Due to the cohesive nature of the molecules lots of energy is needed to break the hydrogen bonds between the molecules. Therefore lots of heat can be absorbed before its temperature raises a significant amount

Living organisms are mostly made of water and so must be able to absorb lots of heat energy without its temp increasing much.

Question 15

Explain the large latent heat of vapourisation of water

Answer 15

In water some molecules are moving at faster speeds and have enough kinetic energy to escape the water (evaporation) which causes the average kinetic energy of the water to decrease so water cools down.

-Animals that can sweat can keep cool as it evaporates from the body surface

Question 16

Explain the strong cohesion of water molecules

Answer 16

Due to their polarity, water molecules are attracted to eachother, and form hydrogen bonds
-These hydrogen bonds help hold water together, so they can flow as a continuous stream (mass flow)
-Water moves up the xylem vessels as a continuous stream which allows it to travel up from the roots
Water cohesion leads to surface tension, which allows small animals to live on the surface of water bodies

Question 17

Explain use of water in metabolic reactions

Answer 17

Water is readily involved in hydrolysis and condensation reactions
-Chemical reactions happen most readily when reactants are dissolved in water
-Water is a major raw material in photsynthesis.

Question 18

Explain how water is an important solvent

Answer 18

Substances that are readily dissolved in water:
-gases -oxygen/carbon dioxide
-wastes - ammonia/urea
-inorganic ions - iron ions in haemoglobin, sodium ions in glucose absorption
-small hydrophilic molecules - amino acids, monosaccharides, ATP

Question 19

What does ATP stand for?

Answer 19

Adenosine triphosphate

Question 20

What is the role of ATP?

Answer 20

ATP is an immediate source of energy in metabolic reactions

Question 21

What is the structure of ATP?

Answer 21

Contains a base (adenine) a pentose sugar, and 3 phosphate ions. The phosphates are described as inorganic as they do not contain carbon

Question 22

How is ATP made and broken down?

Answer 22

ATP is made during respiration from ADP, adenosine diphosphate, by the addition of an inorganic phosphate via a condensation reaction and using the enzyme ATP synthase

ATP can be hydrolysed into ADP + Pi using the enzyme ATP hydrolase

Question 23

How does ATP release and transfer energy to other compounds?

Answer 23

By breaking one of the bonds between the inorganic phosphate groups in a hydrolysis reaction, a small amount of energy is released to the surroundings, which can be used in chemical reactions

ATP can also transfer energy to different compounds. The inorganic phosphate released during the hydrolysis of ATP can be bonded onto different compounds to make them more reactive. This is known of phosphorylation, and this happens to glucose at the start of respiration to make it more reactive.

Question 24

What are the properties of ATP?

Answer 24

-ATP release energy in small, manageable amounts so no energy is wasted and cells do not overheat from wasted heat energy - compared to glucose which releases large amounts of energy

-small and soluble to be easily transported around cell - like glucose

-only 1 bond is hydrolysed to release energy immediately - glucose needs several bonds broken to release energy

-can transfer energy to another molecule, enables phosphorylation, making compounds more reactive - glucose contains no phosphate groups so cannot do this

-ATP can’t pass out of the cell, the cell always has an immediate supply of energy - glucose can leave and so the cell can run out of glucose.