Download Topic 1: Cell biology (15 hours)

Topic 7: Nucleic Acids & Proteins (15 hours)
2.7 DNA replication, transcription and translation (BCC p111)
Essential idea: Genetic information in DNA can be accurately copied and can be translated to make the proteins
needed by the cell.
Nature of science:
1. Obtaining evidence for scientific theories—Meselson and Stahl obtained evidence for the semi-conservative
replication of DNA. (1.8)
Understandings:
Applications and skills:
2. The replication of DNA is semi-conservative and
10. Application: Use of Taq DNA polymerase to produce
depends on complementary base pairing.
multiple copies of DNA rapidly by the polymerase
3. Helicase unwinds the double helix and separates the
chain reaction (PCR).
two strands by breaking hydrogen bonds.
11. Application: Production of human insulin in bacteria
4. DNA polymerase links nucleotides together to form a
as an example of the universality of the genetic code
new strand, using the pre-existing strand as a
allowing gene transfer between species.
template. Guidance: The different types of DNA
12. Skill: Use a table of the genetic code to deduce which
polymerase do not need to be distinguished (but see
codon(s) corresponds to which amino acid.
7.1.14).
13. Skill: Analysis of Meselson and Stahl’s results to
5. Transcription is the synthesis of mRNA copied from
obtain support for the theory of semi-conservative
the DNA base sequences by RNA polymerase.
replication of DNA.
6. Translation is the synthesis of polypeptides on
14. Skill: Use a table of mRNA codons and their
ribosomes.
corresponding amino acids to deduce the sequence of
7. The amino acid sequence of polypeptides is
amino acids coded by a short mRNA strand of
determined by mRNA according to the genetic code.
known base sequence.
8. Codons of three bases on mRNA correspond to one
15. Skill: Deducing the DNA base sequence for the
amino acid in a polypeptide.
mRNA strand.
9. Translation depends on complementary base pairing
between codons on mRNA and anticodons on tRNA.
7.1 DNA structure and replication (BCC p343)
Essential idea: The structure of DNA is ideally suited to its function.
Nature of science:
1. Making careful observations—Rosalind Franklin’s X-ray diffraction provided crucial evidence that DNA is a
double helix. (1.8)
Understandings:
Applications and skills:
2. Nucleosomes help to supercoil the DNA.
8. Application: Rosalind Franklin’s and Maurice
3. DNA structure suggested a mechanism for DNA
Wilkins’ investigation of DNA structure by X-ray
replication.
diffraction.
4. DNA polymerases can only add nucleotides to the 3’ 9. Application: Use of nucleotides containing
end of a primer. Guidance: Details of DNA
dideoxyribonucleic acid to stop DNA replication in
replication differ between prokaryotes and
preparation of samples for base sequencing.
eukaryotes. Only the prokaryotic system is expected. 10. Application: Tandem repeats are used in DNA
5. DNA replication is continuous on the leading strand
profiling.
and discontinuous on the lagging strand.
11. Skill: Analysis of results of the Hershey and Chase
6. DNA replication is carried out by a complex system
experiment providing evidence that DNA is the
of enzymes. Guidance: The proteins and enzymes
genetic material.
involved in DNA replication should include helicase, 12. Skill: Utilization of molecular visualization software
DNA gyrase, single strand binding proteins, DNA
to analyse the association between protein and DNA
primase and DNA polymerases I and III.
within a nucleosome.
7. Some regions of DNA do not code for proteins but
have other important functions. Guidance: The
regions of DNA that do not code for proteins should
be limited to regulators of gene expression, introns,
telomeres and genes for tRNAs.
Topic 7: Nucleic Acids & Proteins (15 hours)
7.2 Transcription and gene expression (BCC p355)
Essential idea: Information stored as a code in DNA is copied onto mRNA.
Nature of science:
1. Looking for patterns, trends and discrepancies—there is mounting evidence that the environment can trigger
heritable changes in epigenetic factors. (3.1)
Understandings:
Applications and skills:
2. Transcription occurs in a 5’ to 3’ direction.
8. Application: The promoter as an example of nonGuidance: RNA polymerase adds the 5 ́ end of the
coding DNA with a function.
free RNA nucleotide to the 3 ́ end of the growing
9. Skill: Analysis of changes in the DNA methylation
mRNA molecule.
patterns.
3. Nucleosomes help to regulate transcription in
eukaryotes.
4. Eukaryotic cells modify mRNA after transcription.
5. Splicing of mRNA increases the number of different
proteins an organism can produce.
6. Gene expression is regulated by proteins that bind to
specific base sequences in DNA.
7. The environment of a cell and of an organism has an
impact on gene expression.
7.3 Translation (BCC p362)
Essential idea: Information transferred from DNA to mRNA is translated into an amino acid sequence.
Nature of science:
1. Developments in scientific research follow improvements in computing—the use of computers has enabled
scientists to make advances in bioinformatics applications such as locating genes within genomes and identifying
conserved sequences. (3.7)
Understandings:
Applications and skills:
2. Initiation of translation involves assembly of the
12. Application: tRNA-activating enzymes illustrate
components that carry out the process. Guidance:
enzyme–substrate specificity and the role of
Examples of start and stop codons are not required.
phosphorylation.
3. Synthesis of the polypeptide involves a repeated
13. Skill: Identification of polysomes in electron
cycle of events.
micrographs of prokaryotes and eukaryotes.
4. Disassembly of the components follows termination
14. Skill: The use of molecular visualization software to
of translation.
analyse the structure of eukaryotic ribosomes and a
5. Free ribosomes synthesize proteins for use primarily
tRNA molecule. Guidance: Names of the tRNA
within the cell.
binding sites are expected as well as their roles.
6. Bound ribosomes synthesize proteins primarily for
secretion or for use in lysosomes.
7. Translation can occur immediately after transcription
in prokaryotes due to the absence of a nuclear
membrane.
8. The sequence and number of amino acids in the
polypeptide is the primary structure.
9. The secondary structure is the formation of alpha
helices and beta pleated sheets stabilized by
hydrogen bonding.
10. The tertiary structure is the further folding of the
polypeptide stabilized by interactions between R
groups. Guidance: Polar and non-polar amino acids
are relevant to the bonds formed between R groups.
11. The quaternary structure exists in proteins with more
than one polypeptide chain. Guidance: Quaternary
structure may involve the binding of a prosthetic
group to form a conjugated protein.
Topic 7: Nucleic Acids & Proteins (15 hours)
3.5 Genetic modification and biotechnology (BCC p187)
Essential idea: Biologists have developed techniques for artificial manipulation of DNA, cells and organisms.
Nature of science:
1. Assessing risks associated with scientific research—scientists attempt to assess the risks associated with
genetically modified crops or livestock. (4.8)
Understandings:
Applications and skills:
2. Gel electrophoresis is used to separate proteins or
10. Application: Use of DNA profiling in paternity and
fragments of DNA according to size.
forensic investigations. Guidance: Students should be
3. PCR can be used to amplify small amounts of DNA.
able to deduce whether or not a man could be the
4. DNA profiling involves comparison of DNA.
father of a child from the pattern of bands on a DNA
5. Genetic modification is carried out by gene transfer
profile.
between species.
11. Application: Gene transfer to bacteria using plasmids
6. Clones are groups of genetically identical organisms,
makes use of restriction endonucleases and DNA
derived from a single original parent cell.
ligase.
7. Many plant species and some animal species have
12. Application: Assessment of the potential risks and
natural methods of cloning.
benefits associated with genetic modification of
8. Animals can be cloned at the embryo stage by
crops.
breaking up the embryo into more than one group of
13. Application: Production of cloned embryos produced
cells.
by somatic-cell nuclear transfer. Guidance: Dolly
9. Methods have been developed for cloning adult
can be used as an example of somatic-cell transfer.
animals using differentiated cells.
14. Skill: Design of an experiment to assess one factor
affecting the rooting of stem-cuttings. Guidance: A
plant species should be chosen for rooting
experiments that forms roots readily in water or a
solid medium.
15. Skill: Analysis of examples of DNA profiles.
16. Skill: Analysis of data on risks to monarch butterflies
of Bt crops.