2. Understandings
Statement
Guidance
2.7.U1
The replication of DNA is semi-conservative and depends on complementary base pairing.
2.7.U2
Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.
2.7.U3
DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template.
The different types of DNA polymerase do not need to be distinguished.
2.7.U4
Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
2.7.U5
Translation is the synthesis of polypeptides on ribosomes.
2.7.U6
The amino acid sequence of polypeptides is determined by mRNA according to the genetic code.
2.7.U7
Codons of three bases on mRNA correspond to one amino acid in a polypeptide.
2.7.U8
Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA.

3. Applications and Skills
Statement
Guidance
2.7.A1
Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR).
2.7.A2
Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.
2.7.S1
Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid.
2.7.S2
Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.
2.7.S3
Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence.
2.7.S4
Deducing the DNA base sequence for the mRNA strand.

4. 2.4 Proteins
Amino acids are linked together by condensation to form polypeptides
There are 20 different amino acids in polypeptides synthesized on ribosomes
Amino acids can be linked together in any sequence giving a huge range of possible polypeptides
The amino acid sequence of polypeptides is coded for by genes
A protein may consist of a single polypeptide or more than one polypeptide linked together
The amino acid sequence determines the three-dimensional conformation of a protein
Living organisms synthesize many different proteins with a wide range of functions

5. WHY Protein Synthesis is CELL CONTROL
All metabolic reactions are catalyzed by proteins (enzymes), including energy releasing and energy capturing reactions.
Proteins offer structure to cells and organisms, such as the cytoskeleton.

6. 2.4 Proteins
Amino acids are linked together by condensation to form polypeptides
There are 20 different amino acids in polypeptides synthesized on ribosomes
Amino acids can be linked together in any sequence giving a huge range of possible polypeptides
The amino acid sequence of polypeptides is coded for by genes
A protein may consist of a single polypeptide or more than one polypeptide linked together
The amino acid sequence determines the three-dimensional conformation of a protein
Living organisms synthesise many different proteins with a wide range of functions

7. DNA has the stored information needed to determine the sequence of amino acids in proteins.
There are 20 different amino acids
Some are positive, negative, polar, neutral… so different aa will attract or repel one another
If you think of the aa as a chain like in the picture above, then imagine that some of those beads like each other, and others repel, then the chain will fold to form a 3D structure. That is the protein

9. Structure of Proteins

10. DNA needs RNA! (This links to Topic 2.6)
3 differences between DNA and RNA:
RNA has ribose sugar
RNA is single stranded
RNA contains a nitrogen base called uracil (U) instead of thymine.

11. 3 types of RNA Messenger RNA (mRNA): Ribosomal RNA (rRNA):
copies DNA in the nucleus and carries the info to the ribosomes (in cytoplasm)
Ribosomal RNA (rRNA):
makes up a large part of the ribosome; reads and decodes mRNA
Transfer RNA (tRNA):
carries amino acids to the ribosome where they are joined to form proteins

12. Types of RNA

13. How does DNA make proteins?
Production of proteins requires two steps: transcription and translation
Takes place in the nucleus and cytoplasm respectively.
We will see mRNA involved in transcription and all 3 RNA involved in translation
The coded message of a gene on DNA has specific instructions on how to make each particular protein that our bodies need
Gene: small segments of DNA that carry instructions for making proteins
Note: not all of the DNA codes for proteins—just the genes.

14. Here is a Basic Overview of the Process and the two steps:
In the Nucleus
Make a complimentary copy of the gene
At a Ribosome
Make a protein by reading the genetic code

15. Transcription - occurs in the nucleus
- Process by which a section of DNA is copies into a complementary strand of RNA

16. The Steps of TRANSCRIPTION
1. DNA unwinds and unzips.
2. The instructions from a gene are copied (transcribed) into a complementary strand of RNA—specifically, mRNA.
mRNA is made using base pairing rules:
3. mRNA leaves the nucleus and attaches to a ribosome in the cytoplasm.
gene (DNA): A T C G A A C C A T T A (template)
mRNA : U A G C U U G G U A A U

17. The Steps of TRANSCRIPTION
The proceeded mRNA leaves the nucleus and enters the cytoplasm.                                
mRNA carries the instructions that direct the assembly of a specific protein to a designated area on the ribosome. 
The instructions are carried in a sequence of three nitrogen bases called a codon.

18. Codon Chart
Codon is the code – needed to convert mRNA into protein language.   Each codon (3 nitrogen bases) codes for one amino acid.  This is the genetic code.  The genetic code is universal possible combinations – (see Table 11.1 in book) – Note some do not code for an amino acid, but provide instructions for making a protein (UAA is a STOP codon indicating that the protein chain ends at that point). AUG is a START codon as well as the codon for methionine.
Note that more than one codon can code for the same amino acid.

19. TRANSLATION
Once the message has reached the ribosome, the protein is ready to be assembled. The process of building the protein from the mRNA instructions is called translation. The transfer RNA (tRNA) and the ribosomal RNA (rRNA) are involved in translation. In the cytoplasm, a ribosome attaches to the strand of mRNA like a clothes pin clamped to a close line. tRNA is responsible for carrying the amino acid (the building blocks of proteins) to the ribosome so they can be linked in a specific order that makes up a single protein.

21. Transcription
Each tRNA attaches to only one type of amino acid (correct translation of mRNA depends on the joining of each mRNA codon with the correct tRNA molecule).   How does this happen? One end of the tRNA carries a three-base sequence called an anticodon, which matches up with a particular codon on the mRNA.  They are complementary to each other.  

22. Translation Overview Occurs in the cytoplasm
Process in which a message carried by mRNA is decoded into a protein!
The mRNA code is made up of groups of three nucleotide bases known as codons.
Each of these specify an amino acid. Eg. UGC = Cysteine
Amino acids are the building blocks of proteins.
So, the mRNA will be translated into a protein.

23. Translation Steps: Steps to translation:
mRNA travels to a site in the ribosome in the cytoplasm
The ribosome reads the mRNA code one codon at a time
Amino acids are brought to the ribosome by tRNA (3 bases on tRNA is called an anticodon.) Anticodons match with codons in a complementary base pair fashion.
Amino acids are linked to form a protein!
ribosome travels down mRNA
tRNA continue to bring amino acids to the growing protein
As the correct amino acids are brought to the ribosome by the tRNAs, they are joined together by bonds called peptide bonds to form the protein that the original DNA coded for.

24. Now that you have the basics
More of an IB view

25. WHAT IS THE DIRECTION OF THE ANTI-SENSE STRAND?
2.7.U4 Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
The enzyme RNA polymerase binds to a site on the DNA at the start of a gene (The sequence of DNA that is transcribed into RNA is called a gene).
RNA polymerase separates the DNA strands and synthesises a complementary RNA copy from the antisense DNA strand
It does this by covalently bonding ribonucleoside triphosphates that align opposite their exposed complementary partner (using the energy from the cleavage of the additional phosphate groups to join them together)
WHAT IS THE DIRECTION OF THE ANTI-SENSE STRAND?

26. Sense strand Antisense strand
The section of the DNA transcribed into RNA is called a gene   The strand that is transcribed is called the anti-sense / template strand and is complementary to the RNA sequence    The strand that is not transcribed is called the sense / nontemplate strand and is identical to the RNA sequence (with T instead of U)
Sense strand
Antisense strand

27. 2.7.U5 Translation is the synthesis of polypeptides on ribosomes.
Translation is the process of protein synthesis in which the genetic information encoded in mRNA is translated into a sequence of amino acids in a polypeptide chain
A ribosome is composed of two halves, a large and a small subunit. During translation, ribosomal subunits assemble together like a sandwich on the strand of mRNA:
Each subunit is composed of RNA molecules and proteins
The small subunit binds to the mRNA
The large subunit has binding sites for tRNAs and also catalyzes peptide bonds between amino acids

28. 2.7.S1 Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid. 2.7.S3 Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence. 2.7.S4 Deducing the DNA base sequence for the mRNA strand.
The diagram summarizes the process of protein synthesis. You should be able to use a section of genetic code, transcribe and translate it to deduce the polypeptide synthesized.

29. 2.7.A2 Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.
Diabetes in some individuals is due to destruction of cells in the pancreas that secrete the hormone insulin. It can be treated by injecting insulin into the blood. Porcine and bovine insulin, extracted from the pancreases of pigs and cattle, have both been widely used. Porcine insulin has only one difference in amino acid sequence from human insulin and bovine insulin has three differences. Shark insulin, which has been used for treating diabetics in Japan, has seventeen differences.
Despite the differences in the amino acid sequence between animal and human insulin, they all bind to the human insulin receptor and cause lowering of blood glucose concentration. However, some diabetics develop an allergy to animal insulins, so it is preferable to use human insulin. In 1982 human insulin became commercially available for the first time. It was produced using genetically modified E. coli bacteria. Since then methods of production have been developed using yeast cells and more recently safflower plants.

30. “The Genetic Code is Universal”
2.7.A2 Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.
All living things use the same bases and the same genetic code.
Each codon produces the same amino acid in transcription and translation, regardless of the species.
So the sequence of amino acids in a polypeptide remains unchanged.
Therefore, we can take genes from one species and insert them into the genome of another species.
“The
Genetic Code
is Universal”
restriction
We already make use of gene transfer in industrial production of insulin:

31. 2.7.A2 Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.
E. coli bacteria contain small circles of DNA called plasmids.
These can be removed.
Restriction enzymes ‘cut’ the desired gene from the genome.
The same restriction enzyme cuts into the plasmid.
Because it is the same restriction enzyme the same bases are left exposed, creating ‘sticky ends’
Ligase joins the sticky ends, fixing the gene into the E. coli plasmid.
The recombinant plasmid is inserted into the host cell. It now expresses the new gene. An example of this is human insulin production.

32. The genetic code is universal – almost every living organism uses the same code (there are a few rare and minor exceptions)
As the same codons code for the same amino acids in all living things, genetic information is transferrable between species
The ability to transfer genes between species has been utilized to produce human insulin in bacteria (for mass production)
The gene responsible for insulin production is extracted from a human cell
It is spliced into a plasmid vector (for autonomous replication and expression) before being inserted into a bacterial cell
The transgenic bacteria (typically E. coli) are then selected and cultured in a fermentation tank (to increase bacterial numbers)
The bacteria now produce human insulin, which is harvested, purified and packaged for human use (i.e. by diabetics)

33. Video – Yes, this is Genetic Modification
So, was your idea of genetic modification limited before watching this video?
Extension Video “The Genetic Revolution” on the Nature of Things– Bonus on Test – watch, take notes and write a ½ page reflection