Topic 1b

Question 1

Why is water a polar molecule?

Answer 1

The shared negative electrons are pulled towards the oxygen and so the hydrogen atom is left with a positive charge while the unshared negative electons on the oxygen gives it a negative charge.

Question 2

List the properties of water?

Answer 2

1. Good Solvent
2. Important metabolite
3. High latent heat of vaporistaion.
4. High specific heat capacity
5. Very cohesive.

Question 3

Name the two reactions water is involved in?

Answer 3

Condensation and Hydrolysis

Question 4

What is a hydrogen bond?

Answer 4

A weak bond between a slightly + charged hydrogen atom in one molecule and a slightly - charged atom in another.

Question 5

What is a metabolite?

Answer 5

A substance involved in a metabolic reaction e.g. respiration

Question 6

What makes water a useful solvent?

Answer 6

The fact that it is polar

Question 7

What is a high latent heat of vaporisation?

Answer 7

It means a lot of energy is required to break the hydrogen bonds between water molecules so a lot of energy is used when it evaporates. Lots of heat is needed to convert it from a liquid to a gas.

Question 8

Explain why water has a high specific heat capacity + what is its definition?

Answer 8

It takes a lot of energy to break the hydrogen bonds between water molecules and so the energy needed to raise the temperature of 1 gram by 1 degrees is very high.

Question 9

Why is having a high specific heat capacity a useful property of water?

Answer 9

It can buffer changes in temperature as it doesnt experience rapid temperature chages and so provides a very stable enviroment for organsims, and helps maintain a constant internal body temperature.

Question 10

Why is water being a solvent an important property?

Answer 10

A lot of subtances involved in biological reactions are ionic and so, due to waters polarity, ions become completely surrounded and dissolve. These substances can therefore be transported around the body.

Question 11

Why does water have a high surface tension and why is this beneficial?

Answer 11

Water is very cohesive and so has a high surface tension when it comes into contact with air. It means seat can form droplets, which can evaporate from the skin to cool an organism down.

Question 12

Why does water having a high latent heat of vaporisation useful for organisms?

Answer 12

They can use water loss through evaporation (sweating) to cool down without lsoing too much water. This works as when water evaporates it carries away heat energy from the surface, cooling the surface thus lowering the bodies temperature.

Question 13

Why is it important that water is transparent?

Answer 13

It allows aquatic plants to photosynthesise and means that light

Question 14

Why is it important that water is transparent?

Answer 14

It allows aquatic plants to photosynthesise and means that light rays can penetrate the jelly like fluid that fills the eye so light can reach the retina

Question 15

Explain how water not easily being easily compressed is a useful property?

Answer 15

It can provide support, for example the hydrostatic skeleton of animals such as the earthworm and provides turger pressure in herbaceous plants.

Question 16

What is an inorganic ion?

Answer 16

An ion that does not contain carbon

Question 17

Where do inorganic ions occur?

Answer 17

Cytoplasm of cells and in bodily fluids

Question 18

What ion’s are part of haemoglobin molecules?

Answer 18

Iron ions

Question 19

What is the role of these ions in haemoglobin?

Answer 19

They bind with oxygen to transport around the body

Question 20

Name the ion that is linked to PH?

Answer 20

H+/ Hydrogen ions

Question 21

Which type of ion is involved in moving glucose and amino acids across cell membranes and what is the name of this process?

Answer 21

Sodium ions/Na+ in Co-transport

Question 22

What does ATP stand for?

Answer 22

Adenosine triphosphate

Question 23

Describe the structure of a molecule of ATP?

Answer 23

A molecule of adenine, a molecule of ribose and three phosphate molecules.

Question 24

How is ATP broken down?

Answer 24

ATP is broken down by a hyrolysis reaction into ADP and Pi. A phosphate bond is broken and energy is released. The reaction is catalysed by ATP hydrolase.

Question 25

How can inorganic phosphate be used?

Answer 25

It can be used to phosphorylate another compound often making it more reactive.

Question 26

What reaction occurs between ADP and Pi and why would this take place?

Answer 26

ATP can be resynthesised in a condensation reaction between ADP and Pi, catalysed by the enzyme ATP synthase. This happens during photosynthesis and respiration.

Question 27

Why is ATP and better immediate energy source than glucose?

Answer 27

- Each ATP molecule releases less energy than each glucose molecule and energy can therefore be released in smaller more manageable quantities. - The hydrolysis of ATP to ADP is a single reaction that releases immediate energy wheras the breakdown of glucose is a long series of reactions and so takes much longer.

Question 28

What energy requiring processes is ATP used for?

Answer 28

Metabolic processes- building macromolecules from basic units. Movement- ATP provides energy for muscle contraction, so filaments of muscle slide past one another shortening the length of the muscle fibre. Active transport- Provides energy to change the shape of plasma proteins into carrier protein, allowing molecules or ions to be moved against a concentration gradient. Secretion- ATP is needed to to form the lysosomes needed for the secretion of cell products. Activation of molecules- Pi can be used to phosphorylate other compounds making them more reactive thus lowering the activation energy.

Question 29

How does ATP store energy?

Answer 29

The bonds between the phosphate groups are unstable and so have a low activation energy which can easily be broken, however when they do break they release a considerable amount of energy.

Question 30

What is the function of DNA?

Answer 30

To store genetic infomation

Question 31

What are ribosomes made from?

Answer 31

Ribosomal RNA and proteins

Question 32

Describe the structure of a DNA nucleotide?

Answer 32

A phosphate group, a deoxribose sugar and a nitrogen containing organic base linked by condensation reactions.

Question 33

Name the four possible bases in DNA?

Answer 33

Adenine, Thymine, Guanine and Cytosine

Question 34

How is a polynucelotide chain formed?

Answer 34

This is many nucelotides joined together in condensation reactions between the phosphate group of one nucleotide and the pentose sugar of another forming a phophodiester bond. The chain of phosphates and sugars is caalled the sugar phosphate backbone

Question 35

Describe how the DNA helix is formed?

Answer 35

Two DNA polynucleotide strands join together by hydrogen bonding between the complementary base pairs- A with T, C with G. Three H bonds form with C and G, Two with A and T. The antiparallel strands then twist around each other to form the DNA double helix.

Question 36

Name the sugar in RNA?

Answer 36

Ribose

Question 37

Name the four bases in RNA?

Answer 37

A, T, G and Uracil

Question 38

Describe the deifferences between RNA and DNA?

Answer 38

DNA is long and double stranded wheras RNA is short and single stranded. DNA contains deoxyribose pentose sugar, RNA has ribose. DNA contains ATCG, wheras RNA has AUCG

Question 39

Who and when worked out the structure of DNA?

Answer 39

In 1953 James Watson and Francis Crick after following the work done by Rosalind Franklin.

Question 40

Why is DNA a stable molecule?

Answer 40

The phophodiester bonds help protect the more chemically reactive bases inside the double helix. Hydrogen bonds link the base pairs forming bridges/rungs between the phosphodiester uprights. As C and G have 3 H bonds the higher the quantity the more stable the DNA molecule.

Question 41

How is DNA adapted to carry out it's functions?

Answer 41

- Very stable structure that rarely mutates. - Two seperate strands joined by H bonds which allow them to seperate during DNA replication and protein synthesis. - Large so can carry a lot of genetic infomation. - Base pairing means DNA replicate and transfer genetic infomation as RNA. - As the base pairs are within the helical cylinder the gentic infomation is protected by outside chemical and physical forces.

Question 42

Why is the process of DNA replication described as semi conservative?

Answer 42

Because half of the strands in the new DNA molecule are from the original DNA molecule, providing genetic continuity between generations of cells.

Question 43

Describe the 1st stage of replication?

Answer 43

The enzyme DNA helicase breaks the bonds between the bases on the two polynucletide strands, making the helix unwind leaving two seperate strands.

Question 44

Describe the 2nd stage of replication?

Answer 44

Each original strand of DNA acts as a template strand for a new strand. Complimentary base pairing takes place between the free floating DNA nucleotides and the exposed bases on the original template strands.

Question 45

Describe the 3rd stage of replication?

Answer 45

The enzyme DNA polymerase joins the nucletides together in condensation reactions, where hydrogen bonds are formed.

Question 46

How does DNA polymerase act on the DNA strands?

Answer 46

Each end of DNA has a different structure, one end is 3' one end is 5', DNA polymerase is only complimentary to the 3' end and so enzymes can only be added to the new strand at the 3' end. This means the new strand is formed in a 5' to 3' direction and DNA polymerase moves down the template strand in a 3' to 5' direction.

Question 47

Who theorised semi conservative replication?

Answer 47

Meselson and Stahl.

Question 48

Describe the experiment that provided eveidence for semi conservative replication?

Answer 48

Two samples of bacteria were grown, on in N14 the other in N15, as the bacteria reproduced they took up nitrogen from the broth to help make nucleotides for new DNA. A sample of DNA was taken from both smaples and spun in a centrifuge, the DNA from N15 settles lower as it was heavier. Then this sample was placed in a broth of N14 and later a sample was spun in the centrifuge. The DNA settled in between where N14 and N15 settled, showing that the DNA contained both N14 and N15.