Biological Molecules - Section 2

Question 1

What is the role of DNA in living organisms

Answer 1

Copies genetic information

Question 2

What is the role of RNA in living organisms

Answer 2

Transfer genetic code

Question 3

What are ribosomes formed from?

Answer 3

Formed by mRNA from DNA into ribosomes.

Question 4

What are the organic bases of DNA?

Answer 4

Cytosine, thymine, adenine, guanine

Question 5

What are the organic bases in RNA ?

Answer 5

Adenine, cytosine, guanine, uracil

Question 6

What is the difference in organic bases between DNA and RNA?

Answer 6

DNA has a thymine base whereas RNA has uracil.

Question 7

What reaction joins two nucleotides and what bond is formed>

Answer 7

Phosphodiester bonds in condensation reactions

Question 8

How many bases make up a codon?

Answer 8

Three

Question 9

Why could a change in the sequence of bases result in a non functional enzyme?

Answer 9

If there is a mutation in a gene for an enzyme, its secondary and tertiary structure (so its active site) could change. It therefore wouldn’t be able to bind to the enzyme.

Question 10

What reaction joins the organic bases in dna ?

Answer 10

Condensation.

Question 11

Desirable the overall structure of DNA?

Answer 11

DNA has a phosphate group, a nitrogen containing base and deoxyribose. It is a long polymer and is double stranded.

Question 12

Compare the structure of RNA to DNA?

Answer 12

RNA is a short polymer, single stranded

DNA is a long and double stranded

Question 13

Describe the stages of semi- conservative replication of dna ?

Answer 13

A section of DNA needs to be replicated
DNA helicase unwinds the two strands of dna by breaking bonds between the bases
Free nucleotides are activated and bind to their complimentary bases
The nucleotides are joined by DNA polymerase which forms phosphodiester bonds
All of the nucleotides are joined to form a complete polynucleotide chain, two identical strands of DNA are formed.

Question 14

What is the role of DNA helicase in semi-conservative replication?

Answer 14

Unwinds the dna by breaking the hydrogen bonds

Question 15

What is the role of DNA polymerase in semi-conservative replication?

Answer 15

DNA polymerase joins nucleotides by forming phosphodiester bonds

Question 16

Why is it called semi-conservative replication ?

Answer 16

Contains one new strand and one old strand

Question 17

In which direction are nucleotides added to a dna strand, and why can it only happen in this direction?

Answer 17

Can only be added in the 5’ to 3’ direction because the nucleotides shapes and alignments are different and DNA polymerases’ active site has a specific shape with the nucleotide only being complimentary at the 3’ end.

Question 18

Describe the experiment used the method of dNA replication was semi-conservative.

Answer 18

They began by growing E. coli in medium, or nutrient broth, containing a “heavy” isotope of nitrogen, 15N

Then, the bacteria were switched to medium containing a “light”
14N. isotope and allowed to grow for several generations.

method separates molecules such as DNA into bands by spinning them at high speeds in the presence of another molecule, such as cesium chloride, that forms a density gradient from the top to the bottom of the spinning tube.
Found that after the first replication the DNA bond was intermediate so contained heavy and light nitrogen
Then after the second replication either a mixture of two new strands or one of each.

Question 19

How is energy released from ATP?

Answer 19

The energy in atp is stored in High energy bonds between the phosphate groups. ATP can be hydrolysed to break one of these phosphate groups

Question 20

What is hydrolysis?

Answer 20

Chemical reaction by the addition of water.

Question 21

Which enzyme catalysed the hydrolysis of ATP?

Answer 21

ATP hydrolyse

Question 22

What is formed when ATP is hydrolysed ?

Answer 22

ADP + Pi

Question 23

What is the phosphate released during the hydrolysis of ATP used for?

Answer 23

Inorganic phosphate can be used to phosphorylation to other compounds

Question 24

Why is ATP a more useful energy source than glucose?

Answer 24

ATP is broken down in a single reaction so energy is released rapidly.

Question 25

How is ATP reformed?

Answer 25

In a condensation reaction :
Photophosphorylation
Oxidative phosphorylation
Substrate level phosphorylation

Question 26

What enzyme catalyses the reaction when ATP is reformed ?

Answer 26

ATP synthase

Question 27

Describe the structure of water

Answer 27

Contains slight positive and slightly negative electrons

Polar molecule

Question 28

Why is water considered a polar molecule ?

Answer 28

It has a positive end and negative end

Question 29

Describe how waters structure and properties links to its metabolite in many metabolic reactions

Answer 29

Useful in breaking down complex molecules by hydrolysis, condensation reactions, chemical reactions, photosynthesis.

Question 30

Water: important solvent in which metabolic reactions occur

Answer 30

Water is polar and readily dissolves in gases, wastes, inorganic ions and enzymes.

Question 31

Water: relatively high heat capacity

Answer 31

=the amount of thermal energy required to rise the temperature of 1kg of substance by 1%
Due to the hydrogen bonds, water specific heat capacity is high. This means water acts as a buffer to sudden temerpature variation because water can absorb a lot of thermal energy.

Question 32

Water: large latent heat vaporisation

Answer 32

Takes a lot of energy to break hydrogen bonds between molecules.
Maintains body temperature on living organisms e.g sweating.
Body heat is used to evaporate water there fore large amounts of thermal energy are lost, leading to a fall in body temperature.

Question 33

Water: strong cohesion between water molecules

Answer 33

=tendency of water molecules to stick together
Hydrogen bonds give water a large cohesive forces
Allow water to be pulled up through a tube e.g xylem, transpiration

Question 34

How do the properties of water allow living organisms to maintain their optimum temperature?

Answer 34

It’s large latent heat evaporation it’s high specific heat capacity maintains its optimum temperature. The hydrogen bonds are difficult to break.

Question 35

Where are the inorganic ions found in living organisms?

Answer 35

Found in the cytoplasm and body fluids

Question 36

Give four examples of ions, and their specific roles linking to their properties

Answer 36

Hydrogen ions= react with proteins. ( changes tertiary structure, enzyme denatured, no enzyme- substrate complex formed.
Iron ions= important in haemoglobin . Iron binds to and carries oxygen.
Sodium ions= important in helping other molecules move across membranes (co-transport), movement of sodium ions helps move other molecules across (glucose e.g)
Phosphate ions= essential compound of nuclei chemical acids (enable the formation of phosphodiester bonds)