1. DNA and Genes
Chapter 11

2. What is DNA? Our genes are located on chromosomes.
Chromosomes are made of DNA - deoxyribonucleic acid.
DNA contains the instructions for making proteins.

3. Structure of DNA
DNA is a long polymer of repeating subunits called nucleotides.
Nucleotides – deoxyribose (sugar), phosphate group, and a nitrogen base.
Four possible nitrogen bases: adenine (A), guanine (G), cytosine (C), thymine (T).

4. Structure of DNA cont.
Nucleotides join together to form long chains, with the phosphate group of one bonding to the sugar of the next.
Backbone – sugar and phosphate groups
Middle (rungs) – base pairs held together by hydrogen bonds

5. Structure of DNA cont. Adenine always pairs with thymine.
Cytosine always pairs with guanine.
Two chains of DNA join together to form a double helix (twisted ladder).
Structure discovered by Watson & Crick in 1953.

6. Nucleotide Sequence
All organisms contain DNA made of nucleotides with the same four bases.
Differences between organisms come from the sequence of the four bases along the DNA strand.
Nucleotide sequence is the unique genetic information of an organism.
The closer the relationship between two organisms, the greater the similarity in their DNA.

7. DNA REPLICATION DNA replication is called ‘semi-conservative’.
2. Semi-conservative replication is the process in which the original strands of DNA remain intact and act as templates for the synthesis of duplicate strands of DNA.

8. DNA REPLICATION
3. One copy of a DNA molecule will split apart to make two complete copies of itself. Each new DNA molecule is made up of half of the old molecule and half of a new molecule.
ANIMATION:

9. STEPS TO DNA REPLICATION
UNZIPPING: The DNA molecule ‘Unzips’ as the hydrogen bonds between the base pairs are broken. The enzyme HELICASE causes this unzipping to occur.

11. STEPS TO DNA REPLICATION
2. COMPLEMENTARY BASE PAIRING: Complementary nucleotides move into position to bond with the complementary bases on the DNA chain.

12. STEPS TO DNA REPLICATION
3. FORM NEW SUGAR PHOSPHATE BACKBONE: The nucleotides join as the sugars and phosphates bond to form a new backbone. This process occurs due to the enzyme DNA POLYMERASE which also checks for mistakes as it goes.

13. STEPS TO DNA REPLICATION
4. This process continues along the primary chain until we have 2 IDENTICAL STRANDS of DNA molecules (assuming there have been no errors made).

15. Replication of DNA
DNA Replication – process that copies the DNA in the chromosomes.
Occurs before cell division.
Each single strand of DNA serves as a template to reconstruct the other strand.
DNA Replication Animation

16. How DNA Replicates
Hydrogen bonds between bases are broken and the DNA molecule “unzips”.
Free nucleotides bond to the exposed single strands by base pairing.
This continues until the whole molecule has been unzipped and replicated.

17. How DNA Replicates cont.
Each new DNA molecule formed contains one parent strand and one newly synthesized strand.

18. RNA RNA – ribonucleic acid
Three major differences between RNA and DNA:
- RNA is a single strand
- RNA’s sugar is ribose
- RNA contains the base uracil (U) instead of thymine (T)

19. RNA vs DNA

20. RNA cont. RNA molecules are responsible for protein synthesis.
There are three types of RNA:
- Messenger RNA (mRNA) carries message from DNA to ribosome
- Ribosomal RNA (rRNA) IS the ribosome
- Transfer RNA (tRNA) Transfers Amino Acids

21. The Genetic Code mRNA carries the instructions for building a protein.
Instructions are written in three-letter words called codons.
Each codon stands for one of twenty amino acids.
Proteins are chains of amino acids in the order coded on the mRNA

22. The Genetic code
3 codons are used as stop signals; they are found at the end of every gene and mark the end of the protein.
One codon is used as a start signal: it is at the start of every protein

23. RNA Genetic Code

24. Central Dogma
In order to make protein, DNA must be transcribed into mRNA.
mRNA leaves the nucleus and is translated into protein in the cytoplasm.

25. Transcription First the DNA “unzips”, just like during replication.
Free RNA nucleotides match up with the exposed DNA nucleotides by base pairing. (A – U, G – C)
The completed mRNA molecule breaks away and the DNA molecule “zips” back together.
mRNA can leave the nucleus, carrying instructions to the cytoplasm.
Transcription Animation

26. Translation
Translation – process of converting the information in a sequence of nitrogen bases in mRNA into a sequence of amino acids in a protein.
Takes place at the ribosomes (rRNA) in the cytoplasm.
As the ribosome moves down the mRNA strand, transfer RNA (tRNA) brings in the appropriate amino acid.

27. Translation cont. Each tRNA has an anticodon of three nitrogen bases.
The tRNA anticodon matches with a mRNA codon.
tRNA also carries an amino acid to add to the growing protein.

29. Transcription Steps
1. The AUG start___________ is recognized by _____________inside the ribosome.
2. Once the start _________ has been found, mRNA is decoded by tRNA (transfer RNA) molecules.
3. The ____________ each transport specific amino acids to the growing chain. This chain forms a __________________.
Translation ends when a stop codon (UAA, UAG, UGA) is reached.

30. Translation