1. KEY CONCEPT DNA structure is the same in all organisms.

2. We love D N A
Made of nucleotides
Sugar, Phosphate and a Base
Bonded down one Side
Adenine and Thymine
Make a Lovely Pair
Cytosine without Guanine
Would feel very bare
O-O-O deoxy-ribo-nucleic acid
R-N-A is ribo-nucleic acid

3. DNA is made up of a long chain of nucleotides
Each nucleotide has three parts
Sugar – deoxyribose
Phosphate group
a nitrogen-containing Base
phosphate group
deoxyribose (sugar)
nitrogen-containing
base

4. The nitrogen containing bases
- Adenine (A)
- Thymine (T)
- Cytosine (C)
- Guanine (G)
* Purines – have 2 rings = Adenine & Guanine
* Pyrimidines – have 1 ring = Cytosine & Thymine

5. Watson and Crick determined the three-dimensional structure of DNA
1953
Two nucleotide chains that wrap around each other to form a double spiral (double helix)
Temperature liable – a change in T can break apart the DNA strand

6. Rosalind Franklin and Erwin Chargaff.
Franklin’s x-ray images suggested that DNA was a double helix of even width.
Chargaff’s - Complementary Base Pairing - A=T and C=G

7. Nucleotides always pair in the same way.
Because a pyrimidine (single ring) pairs with a purine (double ring)
A-T
C-G C G T A

8. The backbone is connected by covalent bonds Very Strong
The bases are connected by hydrogen bonds
Easily formed & easily broken
hydrogen bond
covalent bond

9. 8.3 DNA Replication DNA is replicated during the S phase of interphase
Inside the nucleus

10. DNA serves as a template.
8.3 DNA Replication
DNA serves as a template.
1. Helicase – (Enzyme) breaks the Hydrogen bonds between the bases
Replication Fork – point at which the two chains separate (last bond broken)
nucleotide
The DNA molecule unzips in both directions.

11. 8.3 DNA Replication
New complimentary nucleotide bases pair up on both sides of old DNA template
A pairs up with complement T
C pairs up with complement G
DNA polymerase (Enzyme) forms new Hydrogen bonds between the nucleotides
DNA polymerase
new strand
nucleotide

12. 8.3 DNA Replication
Two new exact copies of DNA are formed, each with an original strand and a newly formed strand.
original strand
new strand
Two molecules of DNA

13. Replication is fast and accurate.
8.3 DNA Replication
Replication is fast and accurate.
DNA replication starts at many points in eukaryotic chromosomes.
Mutation – change in the nucleotide sequence
DNA polymerases can find and correct errors.
One error per 1 billion nucleotides

14. 8.4 Transcription RNA differs from DNA in three major ways. RNA
Sugar = Ribose
Base - Uracil instead of thymine.
U - A
3. Shape - single-stranded

15. 8.4 Transcription Three types of RNA.
Mesenger RNA (mRNA) – single uncoiled chain
carries genetic information from the DNA in the nucleus to the cytoplasm
Transfer RNA (tRNA) – single chain of about 80 nucleotides
folded into a hairpin shape
binds to specific amino acids
Ribosomal RNA (rRNA) – makes up the ribosomes where proteins are made

16. 8.4 Transcription Process of copying DNA into mRNA
Transcription starts when
RNA polymerase (enzyme) - binds to a Promoter on DNA
breaks H-bonds and makes H-bonds
One chain is used as a template
mRNA = transcript
Transcription stops when
RNA polymerase reaches a Terminator
start site
nucleotides
transcription complex

17. Transcription vs Replication.
Replication copies all the DNA
Transcription copies only a gene.
growing RNA strands
DNA
one
gene

18. 8.5 Translation
KEY CONCEPT Translation converts an mRNA message into a protein.

19. Amino acids are coded by mRNA base sequences.
8.5 Translation
Amino acids are coded by mRNA base sequences.
Codon – 3 nucleotides of mRNA
AUG = start
UAA, UAG, UGA = stop
codon for
methionine (Met)
leucine (Leu)

20. 8.5 Translation
The genetic code matches each codon to its amino acid

22. 8.5 Translation tRNA – transports amino acids to the ribosomes
Anticodon – tRNA sequence of 3 nucleotides
complementary to an mRNA codon.

23. 8.5 Translation Translation takes place at the Ribosomes
Ribosomes that are attached to the endoplasmic reticulum build proteins for use outside cell
Ribosomes that are free floating make proteins for use inside cell

24. 8.5 Translation
For Translation to begin - Ribosomes attaches to a start codon on mRNA (AUG)
Start codon pairs with the anticodon on tRNA (UAC)
codes for the first amino acid – methionine
may be removed later if not needed

25. 8.5 Translation
Amino acids are bonded together with peptide bonds

26. 8.5 Translation
Once the stop codon is reached, the ribosome releases the protein

27. 8.6 Gene Expression and Regulation
KEY CONCEPT Gene expression is carefully regulated in both prokaryotic and eukaryotic cells.

28. 8.6 Gene Expression and Regulation
An operator is a part of DNA that turns a gene “on” or ”off.”
The lac operon was one of the first examples of gene regulation to be discovered.
has three genes that code for enzymes that break down lactose
– milk sugar

29. 8.6 Gene Expression and Regulation
RNA processing
Introns are nucleotides that are removed from mRNA
Exons are the nucleotides that are spliced together.
Processed mRNA (transcript) goes to ribosome to be made into a protein

30. 8.6 Gene Expression and Regulation
Coding DNA (genes)  make proteins
Humans = 20,000
Non-coding DNA (genes)  make RNA
Transcribed but never Translated
Human = 500
Human Total = ~ 20,500 genes