Nucleic Acids
Describe the function of DNA.
It directs or controls the activities of the cell, and stores and transmits genetic information.
When does DNA replication occur, and why?
Before a parent cell divides, which ensures that each new daughter cell produced receives an exact copy of the genetic information.
Name the two major steps of Protein Synthesis, and where each occurs in a eukaryotic cell.
Transcription - Nucleus
Translation - Cytoplasm
Name a type of protein whose structure and shape is critical to its function.
Enzymes, (Some) Hormones, Receptor Proteins, Antibodies
Name two factors that can affect enzyme function.
Any Two:
Temperature / pH / Inhibitors / Enzyme Concentration / Substrate Concentration
State two structural differences between DNA and RNA.
Any Two:
Double-Stranded V. Single-Stranded
Deoxyribose Sugar V. Ribose Sugar
Thymine V. Uracil
Larger V. Smaller
Explain why DNA replication is described as a semi-conservative process.
Each new DNA molecule produced consists of one original (parent) strand and one newly synthesised strand. One 'old' and one 'new' strand.
A length of mRNA attached to a ribosome codes for the production of a polypeptide that is 120 amino acids long.
How many mRNA nucleotides code for the amino acids in this polypeptide?
J. 40
K. 120
L. 360
M. 720
L. 360
Name the Four Levels of Protein Structure, in the correct order.
1. Primary
2. Secondary
3. Tertiary
4. Quaternary
The specificity of an enzyme for its substrate is determined by the
J. temperature at which the enzyme is operating.
K. concentration of the substrate.
L. active site of the substrate molecule.
M. structure of the enzyme molecule.
M. structure of the enzyme molecule.
A coding strand of DNA has the sequence: AATCCCGAC.
What would be the complementary sequence of the template strand? Include the direction of the strand in your answer.
3' TTAGGGCTG 5'
Name the two enzymes involved in DNA replication and their role in the process.
Helicase - Breaks the weak hydrogen bonds between the bases, separating the two strands.
DNA Polymerase - Joins the sugar and phosphate groups of the nucleotides, forming the sugar-phosphate backbones of the new strands.
The base sequence AGC on the coding strand of a DNA molecule codes for an amino acid.
Identify its corresponding anticodon.
J. UCG
K. AGC
L. TCG
M. UGC
J. UCG
Describe each of the Four Levels of Protein Structure.
1. Primary - Unique sequence of amino acids in the polypeptide chain.
2. Secondary - Coiling or folding of the polypeptide chain into alpha-helices or beta-pleated sheets.
3. Tertiary - Resulting 3D shape of the polypeptide chain.
4. Quaternary - Two or more polypeptide molecules bonded together.
According to the induced-fit model for enzyme action, an enzyme changes shape
J. when it binds to its substrate.
K. and therefore it can work with many different substrates.
L. to be the same as the shape of its substrate.
M. to fit closely to the active site on the substrate.
J. when it binds to its substrate.
Name the sub-unit ('building block') of a DNA molecule and describe and/or draw its structure.
Nucleotide - Made-up of a Phosphate, Sugar (Deoxyribose), and Nitrogenous Base (A, T, C, or G).
If a strand of DNA has its order of bases as ATGTCCG, one of the four final strands would have the base sequence:
J. GCACTTA
K. UACAGGC
L. TACACCG
M. ATGTCCG
M. ATGTCCG
Which of the following combinations correctly identifies the presence or absence of introns and exons in a human gene, and a function of a gene?
Introns - Exons - Function of a Gene
J. Present - Absent - Codes for an amino acid.
K. Absent - Absent - Codes for a polypeptide.
L. Present - Present - Codes for an RNA molecule.
M. Absent - Present - Codes for a protein.
L. Present - Present - Codes for an RNA molecule.
Which one of the following statements is correct?
J. The primary structure of proteins is affected by any change in temperature.
K. The secondary structure of proteins is made up of more than one polypeptide.
L. The tertiary structure of proteins determines the shape of the active site of an enzyme.
M. The quaternary structure of amino acids is affected by a change in pH.
L. The tertiary structure of proteins determines the shape of the active site of an enzyme.
Enzymes speed up the rate of chemical reactions by lowering the activation energy required to start the reaction. Name one way in which they do this.
Any:
1. Bring reactants together in the correct orientation.
2. Bind to the substrate in a way that places strain on its chemical bonds (Induced-Fit).
3. Make the reaction happen in several small steps, each of which only requires a small amount of activation energy, and each of which is catalysed by a different, specific enzyme.
Which of the following statements about DNA in cells is correct?
J. All DNA in eukaryotic cells is bound to proteins in linear chromosomes.
K. DNA in the nucleus of prokaryotic cells is unbound and circular.
L. DNA in the nucleus of eukaryotic cells is unbound.
M. DNA in the mitochondria is unbound and circular.
M. DNA in the mitochondria is unbound and circular.
State a structural property of the eukaryotic DNA molecule and explain how it aids in the replication process.
Either:
Weak Hydrogen Bond - Can easily break and reform, allowing the double helix to separate and expose the bases for pairing.
Complementary Base Pairs - Conserves the base sequence of the molecule (because A always pairs with T and C always pairs with G).
Explain how the presence of one or more additional exons in a final mRNA strand may alter the function of the protein produced.
If there are additional exons, there would be more codons present in the mRNA strand. This would in turn increase the number of amino acids in the polypeptide chain (as each codon codes for one amino acid). An increase in the number of amino acids would change the sequence of the polypeptide chain (Primary Structure), altering how the protein will fold into its 3D shape, and therefore its function (as the function of a protein is determined by its shape).
In 2005, New Scientist magazine reported that green tea contains the compound epigallocatechin gallate (EGCG).
This compound blocks the enzyme dihydrofolate reductase, which is essential to the growth of gastric and oesophageal tumours.
The shape of a part of the EGCG molecule is
J. similar to the shape of the dihydrofolate reductase molecule.
K. similar to the shape of the active site of the dihydrofolate reductase molecule.
L. complementary to the shape of the dihydrofolate reductase molecule.
M. complementary to the shape of the active site of the dihydrofolate reductase molecule.
M. complementary to the shape of the active site of the dihydrofolate reductase molecule.
When soft-centred chocolates are made, the enzyme invertase is used to convert sucrose into the smaller molecules glucose and fructose. This causes the centres of the chocolates to become softer and sweeter.
Explain why invertase must not be heated to temperatures above 45°C.
At higher temperatures, enzymes become denatured. Denaturation changes the shape of the enzyme, and therefore the shape of the active site, which prevents the substrate from binding. This ceases enzyme function.