1. DNA
Chapter 8

2. The main nucleic acids There are 2 main nucleic acids
1. DNA: Deoxyribonucleic Acid
2. RNA: Ribonucleic Acid

3. What is DNA?
Deoxyribonucleic Acid (DNA) is the genetic enzymes that is critical for an organism’s function because they control the chemical reactions needed for life

4. The structure of DNA
DNA is a polymer made of repeating subunits called nucleotides
Nucleotides have three parts: 1. a simple sugar (deoxyribose), 2. a phosphate group, and 3. a nitrogenous base
Nitrogen base
Phosphate group
Sugar (deoxyribose)

5. Parts of the Nucleotide
The simple sugar in DNA, called deoxyribose (dee ahk sih RI bos), gives DNA its name—deoxyribonucleic acid.
The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms

6. Parts of the Nucleotide
A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen.
In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)

7. Parts of the Nucleotide
Nucleotides join together to form long chains, with the phosphate group of one nucleotide bonding to the deoxyribose sugar of an adjacent nucleotide
The phosphate groups and deoxyribose molecules form the backbone of the chain, and the nitrogenous bases stick out like the teeth of a zipper
Each nitrogen base is held together by a hydrogen bond

8. The structure of DNA
Because DNA is composed of two strands twisted together, its shape is called double helix

9. Watson & Crick
In 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases
Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring

10. The importance of the nucleotide sequence
The sequence of nucleotides forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.
Chromosome

11. DNA Replication
Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes
The DNA in the chromosomes is copied in a process called DNA replication
Without DNA replication, new cells would have only half the DNA of their parents

12. Replication of DNA
DNA
Replication
Replication

13. Copying DNA
DNA is copied during interphase prior to mitosis and meiosis.
It is important that the new copies are exactly like the original molecules

14. Copying DNA New DNA molecule New DNA molecule Free Nucleotides
Original DNA Strand
New DNA molecule
New DNA Strand
Free Nucleotides
Original DNA Strand
Original DNA

15. The importance of DNA Scientists use nucleotide sequences to determine
1. evolutionary relationships among organisms
2. to determine whether two people are related
3. to identify bodies of crime victims.

16. RNA
Section 2

17. 3 Parts of the RNA nucleotide
Ribose (sugar)
Phosphate Acid
4 Nitrogen Bases
1. A- Adenine
2. U- Uracil (replaces Thymine)
3. C- Cytosine
4. G- Guanine

18. RNA vs DNA RNA like DNA, is a nucleic acid.
RNA structure differs from DNA structure in three ways.
RNA is single stranded—DNA is double stranded

19. RNA vs DNA
2. The sugar in RNA is ribose - DNA’s sugar is deoxyribose

20. RNA vs DNA
Both DNA and RNA contain four nitrogenous bases, but rather than thymine, RNA contains a similar base called uracil (U).
Uracil forms a base pair with adenine in RNA, just as thymine does in DNA.

21. RNA provides instruction for making protein
RNA takes instructions from DNA on the assembly of proteins, then—amino acid by amino acid—they assemble the protein.
There are three types of RNA that help build proteins.
1. mRNA: messenger RNA
2. tRNA: transfer RNA
3. rRNA: ribosomal RNA

23. How it all works
Messenger RNA (mRNA), brings instructions from DNA in the nucleus to the cell’s factory floor, the cytoplasm
On the factory floor, mRNA moves to the assembly line, a ribosome.
The ribosome, made of ribosomal RNA (rRNA), binds to the mRNA and uses the instructions to assemble the amino acids in the correct order

24. THEN…
Transfer RNA (tRNA) is the supplier. Transfer RNA delivers amino acids to the ribosome to be assembled into a protein
In the nucleus, enzymes make an RNA copy of a portion of a DNA strand in a process called transcription.

25. Transcription vs Replication
The main difference between transcription and DNA replication is that transcription results in the formation of one single-stranded RNA molecule rather than a double-stranded DNA molecule

26. The Genetic Code
The nucleotide sequence transcribed from DNA to a strand of messenger RNA acts as a genetic message, the complete information for the building of a protein
As you know, proteins contain chains of amino acids. You could say that the language of proteins uses an alphabet of amino acids
A code is needed to convert the language of mRNA into the language of proteins

27. Codon
Biochemists began to crack the genetic code when they discovered that a group of three nitrogenous bases in mRNA code for one amino acid. Each group is known as a codon
Sixty-four combinations are possible when a sequence of three bases is used; thus, 64 different mRNA codons are in the genetic code

29. Facts about Codons
Some codons do not code for amino acids; they provide instructions for making the protein
More than one codon can code for the same amino acid.
For any one codon, there can be only one amino acid

30. The Genetic Code All organisms use the same genetic code
This provides evidence that all life on Earth evolved from a common origin

31. Translation: from mRNA to Protein
The process of converting the information in a sequence of nitrogenous bases in mRNA into a sequence of amino acids in protein is known as translation
Translation takes place at the ribosomes in the cytoplasm
In prokaryotic cells, which have no nucleus, the mRNA is made in the cytoplasm
In eukaryotic cells, mRNA is made in the nucleus and travels to the cytoplasm
In cytoplasm, a ribosome attaches to the strand of mRNA

32. Role of Transfer RNA
For proteins to be built, the 20 different amino acids dissolved in the cytoplasm must be brought to the ribosomes
This is the role of transfer RNA

33. Chain of RNA nucleotides
Amino acid
Each tRNA molecule attaches to only one type of amino acid.
Chain of RNA nucleotides
Transfer RNA molecule
Anticondon

34. tRNA

35. The role of transfer RNA
Ribosome
mRNA codon

36. The role of tRNA
Usually, the first codon on mRNA is AUG, which codes for the amino acid methionine
AUG signals the start of protein synthesis
When this signal is given, the ribosome slides along the mRNA to the next codon

37. The role of transfer RNA
Methionine
tRNA anticodon

38. The role of transfer RNA
A new tRNA molecule carrying an amino acid pairs with the second mRNA codon.
Alanine

39. The role of transfer RNA
The amino acids are joined when a peptide bond is formed between them.
Methionine
Alanine
Peptide bond

40. The role of transfer RNA
A chain of amino acids is formed until the stop codon is reached on the mRNA strand.
Stop codon

41. Mutations
Section 3

42. Mutations in reproductive cells
By changing the sequence of nucleotides within a gene in a sperm or an egg cell
The altered gene would become part of the genetic makeup of the offspring
May produce a new trait or a protein that does not work correctly or a protein that is nonfunctional
The embryo may not survive
In some rare cases a gene mutation may have positive effects

43. Mutations in Body Cells
If the cell’s DNA is changed, (by a gamma ray) this mutation would not be passed on to offspring but could cause problems for the individual
Damage to a gene may impair the function of the cell
When that cell divides, the new cells also will have the same mutation
Some mutations of DNA in body cells affect genes that control cell division resulting in cancer

44. Point Mutation
A point mutation is a change in a single base pair in DNA
A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein.

45. example
Normal:
THE DOG BIT THE CAT
Mutation:
THE DOG BIT THE CAR

46. The effects of point mutations
mRNA
Normal
Protein
Stop
Replace G with A
Point mutation
mRNA
Protein
Stop

47. Frameshift Mutation
What would happen if a single base were lost from a DNA strand?
Frameshift mutation is an addition or deletion of a base in a DNA strand

48. Frameshift Mutation
Deletion of U
mRNA
Protein

49. Causes of Mutations
Could be spontaneous, or caused from environmental factors
Any agent that can cause a change in DNA is called a mutagen
* Radiations
*Chemicals
* High Temperatures