DNA contains the genetic instructions for all living things. It is made up of nucleotides, which are composed of phosphate, sugar, and one of four nitrogen bases (adenine, cytosine, guanine, thymine). DNA exists as a double helix structure, with the bases bonding together in specific base pairs. DNA replicates itself before cells divide, and mutations can occasionally occur during this process, potentially causing genetic disorders or diseases. Genes within DNA code for proteins, which carry out all the functions of life. The DNA code is transcribed into RNA and then translated to synthesize proteins through a multi-step process.

2.  DNA (deoxyribonucleic acid).
 All living things contain DNA.
 Source of genetic traits.
 DNA is a nucleic acid.
 Nucleic acids are made of
nucleotides.

3. Nucleotides
 Made of three
things:
1. Phosphate
(PO4)
2. Sugar
(deoxyribose).
3. Nitrogen base.

4. Nitrogen Bases
Four nitrogen bases
makes four different
nucleotides:
–Guanine
–Cytosine
–Adenine
–Thymine

5. Chargaff’s Rule
 He measured amounts of each
base in various organisms and
found:
amt of adenine (A) = thymine (T)
amt of cytosine (C) = guanine (G)
 This meant that A bonds to T
and C bonds to G
 If 20% of strand is A, what %T?
%C?

6. Structure of DNA
 Discovered by Watson and Crick
 Double helix- “spiral staircase”, 2
strands of nucleotides
 Siderails-sugar and phosphate
 Rungs-nitrogen bases
– A----T
– C----G
Hydrogen bonds (glue)

7. What is DNA Replication?
 Replicate = make “exact” copies.
 All DNA must be replicated before a cell can
divide. Why?
 Why do cells need to divide?
1.Growth.
2.Repair or replace
damaged cells.
3.Regenerate body parts
(not all things can do this).

8. Enzymes and Replication
 Helicase- unwinds DNA
 DNA polymerase-moves along each strand
and brings in bases for new strand copy

9. DNA Replication
 Can be a mistake in replication
 Mutations-change in DNA
 Caused by mutagens, such as X-rays,
toxins, drugs, UV light, etc.
 Can cause disease, such as cancer,
cystic fibrosis, etc.
 Can be:
– insertions of extra bases
– deletions of bases
– substitutions of the wrong bases.

10. Mutations
Substitution

11. How Much DNA Is In Our Cells?
 Chromosome-strands of DNA coiled tightly
 Human cell has 46 (23 pair 2 sets of 23)
 23 from Mom
 23 from Dad

13.  If all body cells contain the same # of
chromosomes, why are all cells so
different?
 Different cells make different proteins.
 Different “active” segments of DNA.
 During early stages of development, cells
become “specialized.”

14.  The first few cells that develop from
the zygote are called stem cells.
 Stem cells differentiate into other
cells.

15. 2 Types of Cells
 Body cells somatic
 diploidchromosomes are in pairs (23 pairs)
 Reproductive cellsgametes
 egg & sperm
 haploid no pairs (23)

16. What is the Purpose of DNA?
 The cell “factory” makes proteins.
 Gene- a segment of DNA that codes for a
protein.
 DNA has 1000’s of genes to make many
different types of proteins.
– Fingernails, hair, enzymes, hemoglobin, etc.
 Protein - polymer of amino acids

17. What is the Purpose of DNA?

18. RNA (Ribonucleic acid)
 _____RNA____vs._____DNA___
single strand double strand
sugar= ribose sugar= deoxyribose
A, C, G, U (uracil) A, C, G, T
mRNA, rRNA, tRNA “DNA is DNA”
all over nucleus only

19. Structure RNA

20. Part 1of Protein Synthesis:
Transcription
 Transcription: DNA  RNA (messenger)
 Occurs in nucleus
 DNA complementary to mRNA
 DNA: ATA-CGG-AAT
transcription in nucleus
mRNA: UAU-GCC-UUA

22. Part 2 of Protein Synthesis:
Translation:
 Translation: mRNA  protein
 Occurs at ribosomes in cytoplasm
 Codon-Three bases on mRNA that code for
an amino acid
 mRNA: UAU-GCC-UUA (3 codons)
translation in cytoplasm
protein: a.a.---a.a---a.a.
 mRNA needs the help of tRNA to bring in
the amino acids

23. Whole Process
DNA: ATA-CGG-AAT
transcription in nucleus
mRNA: UAU-GCC-UUA(3 codons)
translation in cytoplasm
protein: a.a.-a.a-a.a.
How do we know what amino acid results?
The Codon chart or wheel!!!

25. The Codon Wheel