Biological molecules

Which option describes the structure of biological molecules?

A Carbohydrates contain only C, H and O, usually with an H to O ratio of 2: 1.

B Nucleic acids contain only C, H, O, N, P and S in variable ratios.

C Proteins contain only C, H, O and N in variable ratios.

D Triglycerides contain only C, H and O, usually with an H to O ratio of 2: 1.

Your answer

Which statement about the structure of amino acids is not true?

A Amino acids contain amino and carboxyl groups.

B Amino acids contain the elements hydrogen, carbon and oxygen only.

C Each amino acid has a unique R group.

D The R groups in amino acids can be polar or non-polar.

Your answer

Vitamins are molecules that are consumed in the diet of animals and have essential roles in the body.

Thin layer chromatography (TLC) was used to separate a mixture of vitamins from a vitamin supplement tablet.

Most vitamins are colourless.

Suggest one method for visualising the vitamins in TLC.

The results of the TLC are shown in the chromatogram in Fig. 2.1.

Use Fig. 2.1 to calculate the R_f value of vitamin B₂.

Vitamin B₉ is needed for the synthesis of molecule D, shown in Fig. 2.2.

Fig. 2.2

Molecule D is a component in the structure of DNA.

A deficiency of vitamin B₉ in the diet can cause interphase to stop in some cells.

Use Fig. 2.2 to explain why a deficiency of vitamin B₉ can cause interphase to stop.

Vitamin B₂ is used by the body to make FAD. Vitamin B₃ is used by the body to make NAD.

A mitochondrion is shown in Fig. 2.3.

Label Fig. 2.3 to show the locations where FAD gains H atoms and where FAD releases H atoms during respiration.

• Use the letter E to show where FAD gains H atoms.

• Use the letter F to show where FAD releases H atoms.

The table lists features that are correct for FAD, NAD, both or neither.

Complete the table by adding a tick (✓) to a box where the feature is correct and a cross (✗) where the feature is incorrect. You should add either a tick or a cross to every box in the table.

ATP is produced in respiration. Some of these molecules of ATP are used to release energy for processes in respiration. For example, ATP is used in the early stages of glycolysis.

Suggest one other way in which ATP contributes to the process of respiration.

Vitamin C affects the activity of enzymes in different ways.

Vitamin C acts as a coenzyme for several enzymes in the synthesis of collagen.

Outline the role of coenzymes in biological reactions.

A scientist investigates the effect of vitamin C on the activity of the enzyme adenylyl cyclase.

Adenylyl cyclase catalyses the conversion of ATP to cAMP.

The scientist measures the activity of adenylyl cyclase without vitamin C and with 1 mmol dm^–3 of vitamin C.

The scientist’s results are shown in Fig. 2.4.

Explain what can be concluded from the results in Fig. 2.4 about the effect of vitamin C on the activity of adenylyl cyclase.

The following table describes the approximate percentage mass of different chemical elements in organic polymers.

Which of the rows, A to D, is correct?

Your answer

The diagram below shows part of a plasma membrane.

Which of the label lines points to a structure that could contain a sulfur atom?

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

Fig. 1.1 shows the structure of the amino acid leucine.

On Fig. 1.1, draw a circle around the R group of leucine.

Students used thin layer chromatography to separate leucine from other amino acids. The chromatogram they produced is shown in Fig. 1.2.

What can you conclude about the chemical properties of leucine and amino acid X?

Amino acid Z was in the mixture analysed by the students. It is not shown on the chromatogram in Fig. 1.2. Amino acid Z has an R_f value that is 0.20 lower than that of amino acid Y.

Place a dot on the chromatogram in Fig. 1.2 to show the distance moved by amino acid Z.

Show your working.

Thin layer chromatography can also be used to separate photosynthetic pigments.

State a material that can be used as the stationary phase in thin layer chromatography.

State the precise location of photosynthetic pigments in a chloroplast.

When sequencing DNA, fragments of DNA are separated by electrophoresis.

Describe three differences between the process of thin layer chromatography and the form of electrophoresis used to sequence DNA.