1. DNA & Genes
Chapter 11

2. Discovery of DNA
The composition of DNA was first described correctly in 1952 by two scientists:
Watson
Crick
They discovered that it was formed from two long chains of nucleotides shaped much like a spiraling ladder.
They called this shape the double helix.

3. DNA: The Molecule of Heredity
Deoxyribonucleic Acid (DNA) is a very long molecule that contains the information of life.
DNA is a polymer made of repeating subunits called nucleotides.
A nucleotide has three parts:
A simple sugar
A phosphate group
A nitrogen base

4. Structure of DNA Simple sugar Phosphate group
The sugar in DNA is deoxyribose
It gives DNA its name
Phosphate group
Composed of one atom of phosphorus surrounded by four oxygen atoms

5. Structure of DNA Nitrogen Base
A carbon ring structure that contains one or more atoms of nitrogen
There are four possible nitrogen bases:
adenine (A)
guanine (G)
cytosine (C)
thymine (T)

7. Nitrogen Bases Purine – double ring nitrogen bases
Adenine (A)
Guanine (G)
Pyrimidine – smaller, single-ring nitrogen bases
Cytosine (C)
Thymine (T)

8. Draw these structures in your notes – Page 288

9. Base-Pairing Rules
The two sides of the double helix are connected together by hydrogen bonds.
Hydrogen bonds form between two nitrogen bases that make up the rungs of the ladder.
The two nitrogen bases on the same rung of the DNA ladder are referred to as a base pair.

10. Base-Pairing Rules for DNA
Guanine always pairs with Cytosine
Adenine always pairs with Thymine
The strictness of base-pairing results in two strands that are complementary. This means the sequence of bases on one strand determines the sequence of bases on the other strand.
Example: T C G A A T T G C
__ __ __ __ __ __ __ __ __

11. Base-Pairing in DNA
All organisms contain chromosomes composed of DNA made up of nucleotides with guanine, cytosine, adenine, and thymine.
The reason organisms can be different from each other even though their genetic material is made of the same molecules is because the order of nucleotides is different.
The sequence of nucleotides is what forms the genetic information of an organism.

12. Base Pairing Review
A T G C G T A T C __ __ __ __ __ __ __ __ __ G C T G A G C G T T A G C T C G G A C G A C G T C A G

13. Base-Pairing Review
How can two organisms be so different from each other if their genetic material is made of the same DNA --- G, C, A, T?
_____ and _____ are called purines because they are a _______ ring of carbon and nitrogen.
_____ and _____ are called pyrimidines because they are a _____ ring of carbon and nitrogen.

14. The Central Dogma
The central dogma describes how information from DNA gets used to make proteins.
The Central Dogma involves three processes:
Replication – copies DNA
Transcription – converts a DNA message into RNA
Translation – interprets RNA into a string of amino acids, called a polypeptide

15. DNA REPLICATION
During mitosis and meiosis, the cells divide. Each time a cell divides, it must make a copy of its DNA.
Replication is the process by which DNA is duplicated, forming two identical copies from one original.

16. 3 Steps to DNA Replication
The enzyme helicase breaks the hydrogen bonds between the nitrogen bases that hold the two strands together – effectively unzipping the DNA molecule.
As the DNA continues to unzip, free nucleotides, from the surrounding area in the nucleus, bond to the two single strands according to the base pair rule.
The enzyme DNA polymerase forms the sugar-to- phosphate bonds that connect the nucleotides on each strand of DNA.

17. DNA REPLICATION
Replication of DNA doesn’t begin at one end of the molecule and proceed to the other.
It occurs simultaneously at many points on the molecule, speeding up the process.
Replication is completed when the entire molecule has been unzipped and replicated.

18. DNA REPLICATION VIDEO

19. TRANSCRIPTION
Transcription is the process of producing RNA (Ribonucleic Acid) from DNA.
RNA is the form of a nucleic acid in which information moves from DNA in the nucleus to the ribosomes in the cytoplasm.
The process of transcription is similar to the process of replication, with one exception:
Adenine pairs with Uracil – not thymine

20. 3 DIFFERENCES BETWEEN DNA & RNA
RNA is single stranded – DNA is double stranded
RNA’s sugar is ribose – DNA’s sugar is deoxyribose
RNA has the base uracil – DNA has the base thymine

21. 3 TYPES OF RNA mRNA – messenger RNA tRNA – transfer RNA
It carries the information from DNA (in the nucleus) out into the cytoplasm.
tRNA – transfer RNA
It brings amino acids to the ribosomes so they can be assembled into proteins.
rRNA – ribosomal RNA
It makes up the ribosomes, which are the site of protein synthesis.

22. COMPARE & CONTRAST REPLICATION & TRANSCRIPTION
Similarities
Both involve unwinding the DNA double helix
Both involve large enzymes called polymerases
Differences
Replication makes an identical copy of DNA, but transcription makes RNA molecules
Replication happens only once during the cell cycle, but transcription happens over and over on the same gene to make many copies

23. Transcription Practice
GATACGATGACG
TACGTTACGCCA
GGTACAACGTGT
GATCGATCAAGC
GCAAACTTACGAG
CGATAGCATCGAT

24. TRANSLATION
Translation is a process that converts a message from one language into another, likewise, Translation happens in your cells too.
Cells translate an mRNA message into amino acids.
A long strand of amino acids are known as a polypeptide, which are the building blocks of proteins – this whole process is called translation.
An mRNA message can be translated into 20 different amino acids.

25. TRANSLATION, CONTINUED
The genetic code consists of four letters that make up 3- letter “words” called codons.
Each 3-letter codon codes for 1 of the 20 amino acids.
Multiple codons can code for the same amino acid. For example, the codons UCU, UCC, UCA, and UCG all code for serine.

26. TRANSLATION, CONTINUED
In addition to codons that code for amino acids, there is a start codon & three stop codons.
The start codon (AUG) signals the start of translation & also codes for the amino acid methionine.
The three stop codons (UAA, UAG, & UGA) signal the end of an amino acid chain.

27. TRANSLATION, CONTINUED
Why have a start codon anyway?
For words to make sense, they must be read starting at the correct place, or with the correct reading frame.
For example:
T HEC ATA TET HER AT
TH ECA TAT ETH ERA T
THE CAT ATE THE RAT
There are no spaces between codons, but the correct start site and the correct reading frame must be used for the message to make sense.

28. TRANSLATION, CONTINUED
The process of translation happens in the cytoplasm of both prokaryotic and eukaryotic cells.
The amino acid chain is bonded together with a peptide bond.
Transcription & Translation are key factors for protein synthesis.
DNA  RNA  Amino Acids  Protein

29. TRANSLATION PRACTICE
AUGGUACUGUAA
GCUAUGUGAUCU
GUAUGCGUGGCGAGUAG

30. MUTATIONS A mutation is any mistake or change in the DNA sequence.
Mutations in gametes can be passed on to offspring of the affected individual, but mutations in body cells affect only the individual in which they occur.
There are two types of mutations:
Chromosome Mutations
Gene Mutations

31. CHROMOSOME MUTATION
A chromosome mutation involves a change in the structure or number of chromosomes.
Explanation of chromosome mutations:
Nondisjuction is when one or more pairs of homologous chromosomes fail to separate during meiosis.
Deletion – a piece of chromosome breaks off completely. After cell division, the new cell will lack a certain set of genes. Often this is fatal to the zygote.

32. CHANGES IN CHROMOSOME STRUCTURE
Insertion (Duplication) – A chromosome fragment attaches to its homologous chromosome, which then carry two copies of a certain set of genes
Inversion – the chromosome piece reattaches to the original chromosome but in a reverse position
Translocation – the piece reattaches to a nonhomologous chromosome

33. GENE MUTATION
Gene mutation involves a change in the chemical makeup of the DNA.
Point mutations occur when one or more DNA nucleotides are deleted or substituted with others.
Frameshift are mutations that change one or just a few nucleotides in a gene on a chromosome
Sickle cell anemia
Cystic Fibrosis

34. MUTATIONS
Occasionally random gene mutations produce changes that make the individual better adapted to the environment. Such mutated genes tend to increase in frequency within a population

35. MUTAGENS
Mutagens are factors that increase the number of occurrences of mutations.
Examples:
Ultraviolet Rays
Radioactive Substances
Chemicals
Nicotine
Alcohol