ATP

Pears are a type of fruit.

When pears ripen, the:

• fructose concentration increases in cell vacuoles

• volume of cell vacuoles increases.

Figure 2 shows information about a pear cell’s vacuole membrane.

• Carrier protein X is linked to an ATP hydrolase enzyme.

• Carrier protein Y co-transports H⁺ ions and fructose molecules in opposite directions.

Explain why the volume of the vacuoles in pear cells increases when pears ripen.

Your answer should refer to the role of:

• ATP hydrolase

• carrier protein X and carrier protein Y.

A respiratory inhibitor caused a change in pH of the solution within the vacuole.

Use information in Figure 2 to explain how.

Explain how a change in the expression of the genes coding for the carrier proteins can increase the rate of ripening of pears.

Describe and explain how you would use cell fractionation and ultracentrifugation to obtain a sample of nuclei from muscle tissue.

Describe the role of organelles in the production and release of enzymes by animal cells.

Do not include details of transcription in your answer.

Describe the structure of ATP.

Outline how named enzymes break down and resynthesise ATP.

Write an essay on one of the topics below.

Either

Phosphorus-containing substances and their importance in biological systems.

Or

The mechanisms and importance of transport within organisms.

Write an essay on one of the topics below.

Either

The uses and importance of ATP in organisms.

Or

The importance of cycles in biology.

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst.

Scientists investigated the action of the enzyme ATP synthase. They made reaction mixtures each containing:

• ATP synthase

• buffer (to control pH)

• substrates.

One of the substrates required in these reaction mixtures is inorganic phosphate (Pi).

Tick () one box to show which other substrate the scientists must add to the reaction mixtures to produce ATP.

The scientists investigated the effect of concentration of inorganic phosphate (Pi) on ATP synthase activity.

After 2 minutes, they stopped each reaction and then measured the concentration of ATP.

Figure 1 shows the scientists’ results.

Suggest and explain a procedure the scientists could have used to stop each reaction.

Explain the change in ATP concentration with increasing inorganic phosphate concentration.

Figure 1 shows a cell from the lining of the ileum specialised for absorption of products of digestion.

SGLT1 is a carrier protein found in the cell-surface membrane of this cell, it transports glucose and sodium ions (Na⁺) into the cell.

The action of the carrier protein X in Figure 1 is linked to a membrane-bound ATP hydrolase enzyme.

Explain the function of this ATP hydrolase.

The movement of Na⁺ out of the cell allows the absorption of glucose into the cell lining the ileum.

Explain how.

Describe and explain two features you would expect to find in a cell specialised for absorption.

Figure 2 is a diagram of one SGLT1 carrier protein.

Figure 2

Draw phospholipids on Figure 2 to show how the carrier protein, SGLT1, would fit into the cell-surface membrane.

Do not draw more than eight phospholipids.

Figure 2 shows the SGLT1 polypeptide with NH₂ at one end and COOH at the other end.

Describe how amino acids join to form a polypeptide so there is always NH₂ at one end and COOH at the other end.

You may use a diagram in your answer.

Space for diagram:

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

Figure 5 shows the percentage of rat cells undergoing DNA replication. Some cells contained a protein called cyclin D and some cells did not contain cyclin D. All cells were in early interphase at time 0

It took less time for 25% of cells with cyclin D to be undergoing DNA replication than for 25% of cells without cyclin D.

Use Figure 5 to calculate this time difference as a percentage decrease.

Show your working.

Cyclin D stimulates the phosphorylation of DNA polymerase, which activates the DNA polymerase.

Describe how an enzyme can be phosphorylated.

Some tumour cells contain higher than normal concentrations of cyclin D.

Use Figure 5 to suggest why higher than normal concentrations of cyclin D could result in a tumour.

In women, the first division of meiosis produces one daughter cell that has almost all of the cytoplasm. The other daughter cell consists of a nucleus surrounded by a very small amount of cytoplasm and a cell-surface membrane. This very small daughter cell is called a polar body. Polar bodies do not usually divide. The same process occurs in the second division of meiosis, resulting in one egg cell and two polar bodies.

The diagram in Figure 3 shows the formation of an egg cell and two polar bodies during meiosis. It also shows what happens to one pair of homologous chromosomes. This pair carries two alleles of gene A.

Complete Figure 3 by putting A or a in the boxes. One box has been completed for you with A.

combination of alleles on the chromosome in the first polar body in Figure 3.

A scientist measured the diameter of a polar body and the diameter of the nucleus inside it. The diameter of the polar body was 10.4 µm and the diameter of the nucleus was 7.0 µm. The density of mitochondria in the cytoplasm of the polar body (outside of the nucleus) was 0.08 mitochondria per µm³.

Calculate the number of mitochondria in the polar body. You should assume polar bodies and nuclei are spherical.

The formula for the volume of a sphere is πr³ where π = 3.14

Show your working.

Mitochondrial diseases are caused by faulty mitochondria. All of a person’s mitochondria are inherited from their mother via the egg cell. An egg cell contains

One proposed treatment to prevent passing on faulty mitochondria involves

• removing the nucleus from an egg cell donated by a woman with healthy mitochondria

• replacing this nucleus with the contents of the polar body from a woman whose egg cells are affected by mitochondrial disease.

Suggest how this treatment prevents inheritance of mitochondrial diseases.

If most of the mitochondria in a cell are faulty, this prevents many important enzyme-catalysed reactions taking place or slows them down.

Suggest and explain one reason why.

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Scientists investigated treatment of a human bladder infection caused by a species of bacterium. This species of bacterium is often resistant to the antibiotics currently used for treatment.

They investigated the use of a new antibiotic to treat the bladder infection. The new antibiotic inhibits the bacterial ATP synthase enzyme.

Place a tick () in the appropriate box next to the equation which represents the reaction catalysed by ATP synthase.

The new antibiotic is safe to use in humans because it does not inhibit the ATP synthase found in human cells.

Suggest why human ATP synthase is not inhibited and bacterial synthase is inhibited.

The scientists tested the new antibiotic on mice with the same bladder infection. They divided these mice into three groups, C, R and A.

Group C was the control (untreated).

Group R was treated with an antibiotic currently used against this bladder infection.

Group A was treated with the new antibiotic.

They removed samples from the bladder of these mice after treatment and estimated the total number of bacteria in the bladder.

Their results are shown in Figure 2.

The antibiotics were given to the mice at a dose of 25 mg kg^–1 per day.

Calculate how much antibiotic would be given to a 30 g mouse each day.

Show your working.

Calculate the percentage difference in actual numbers of bacteria in group A compared with group R. The actual number of bacteria can be calculated from the log₁₀ value by using the 10^× function on a calculator.

Show your working.

The scientists suggested that people newly diagnosed with this bladder infection should be treated with both the current antibiotic and the new antibiotic.

Explain why the scientists made this suggestion.

Use information from Figure 2 and your knowledge of evolution of antibiotic resistance in bacteria in your answer.

Write an essay on one of the topics below.

EITHER

The importance of nitrogen-containing substances in biological systems.

OR

The importance of diffusion in organisms.