1. What is DNA? Instructions for making proteins
‘Blueprint’ for who we are
Where is it found?
Found in the nucleus
What does ‘DNA’ stand for?
Deoxyribonucleic Acid

2. The Structure of DNA
Double helix
Structure of DNA: Twisted Ladder

3. Who Discovered DNA’s Structure?
SCANDAL! Read all about it!
Rosalind Franklin, James Watson, Francis Crick, & Maurice Wilkins discovered the shape (double helix) of DNA is 1953.

4. DNA is a polymer of Nucleotides. What are the 3 parts of a nucleotide?
THINK!
DNA is a polymer of Nucleotides.
What are the 3 parts of a nucleotide?

5. Nucleotides
DNA Subunit
3 components
a sugar
a phosphate group
a nitrogen base

7. Nitrogen Bases 4 Types: Adenine Thymine Guanine Cytosine REMEMBER:
At The Golf Course

8. Complementary Base Pairs
Nitrogen bases always pair with the same partner
Adenine & guanine are double-ringed structures and are called purines.
Thymine & cytosine are single ringed and are called pyrimidines.
Hydrogen bonds hold
the bases together.
A--T (At--The)G-C (Golf--Course)

9. THINK! What would the complementary strand be?
A-T-C-C-G-T-T-T-A-C-A-G-G-A
T-A-G-G-C-A-A-A-T-G-T-C-C-T

10. Nucleotides join to form long chain (polymer) Sides of the ladder:
How DNA Strands Form
Nucleotides join to form long chain (polymer)
Sides of the ladder:
Sugar + Phosphate
Rungs of ladder:
Nitrogen bases bond together

11. How is DNA Organized?
Histone proteins act like spools that wind up DNA to keep it organized.

12. During Interphase…
How does DNA exist?
Unwound! (Chromatin)

13. Why Chromatin? What happens during Interphase?
DNA Replicates!
DNA is uncoiled so that enzymes can unzip it.
When it is unzipped, DNA can be duplicated.

14. DNA Replication
Process where DNA is copied
Occurs before mitosis and meiosis (during interphase!)

15. How DNA Duplication Occurs
Step 1: Enzymes unzip the DNA strand T A G C
ENZYME

16. Step 2: Free nucleotides bind to the complementary bases.G C

17. Result: 2 Complete Strands!G C

18. Semiconservative Replication: one of the original strands is present in each new strand of DNA.

19. Transcription & Translation DNA to mRNA to Protein
Protein Synthesis
Transcription & Translation
DNA to mRNA to Protein

20. RNA There are three kinds of RNA:
Messenger RNA (mRNA): takes message from DNA in nucleus to the ribosomes in cytoplasm
Ribosomal RNA (rRNA): makes up the structure of ribosomes
Transfer RNA (tRNA): transfers amino acids to ribosome to be assembled into a protein

21. Nucleus RNA transcription
Enzyme RNA polymerase copies a strand of DNA into a complementary mRNA molecule
Similar to DNA replication, but only one new strand is made
mRNA molecule leaves the nucleus & moves to the ribosome
Making mRNA transcript is the first step in protein synthesis (DNA to mRNA)

22. The Genetic Code DNA contains the code to make proteins
Triplet: 3 nucleotides in a row in DNA that codes for one amino acid
Codon: 3 nucleotides in mRNA that code for one amino acid
Anticodon: 3 nucleotides in tRNA that pairs with mRNA

23. Strand to be transcribed
DNA
Figure 10.8B Deciphering the genetic information in DNA.

24. Strand to be transcribed
DNA
Transcription
RNA
Figure 10.8B Deciphering the genetic information in DNA.
Start
codon
Stop
codon

25. Second base
First base
Third base

26. Strand to be transcribed
DNA
Transcription
RNA
Figure 10.8B Deciphering the genetic information in DNA.
Start
codon
Stop
codon
Translation
Polypeptide
Met
Lys
Phe

27. Ribosomes No membrane Made of 1 small and 1 larger subunit
Constructed by nucleolus
Ribosome is essentially a ‘big enzyme’
RNA translation : the rest of the process of making proteins (mRNA to protein)
There are 20 different amino acids
The order and number of amino acids in the protein make one protein different from another protein

28. The Ribosome tRNA-binding sites A site P site Large subunit mRNA
tRNA-binding sites
A site
P site
Large
subunit
mRNA
binding
site
Small
subunit

29. Translation: mRNA to Protein
Ribosomes ‘read’ 3 base sequences of mRNA at a time= codon
Each codon is the code for a specific amino acid
Codon on mRNA complements anticodon of tRNA carrying amino acids to the ribosome

30. Next amino acid to be added to polypeptide Growing polypeptide
Next amino acid
to be added to
polypeptide
Growing
polypeptide
anticodons
tRNA
mRNA
Figure 10.12C A ribosome with occupied binding sites.
This figure shows that one of the tRNA binding sites (P site) holds the growing peptide chain while the adjacent site (A site) holds the tRNA carrying the next amino acid to be added to the chain.
Codons

31. Translation Requires three steps:
1) initiation, 2) elongation, 3) termination.
Initiation
Small ribosome subunit binds to mRNA
All proteins begin with start codon AUG (methionine) and pairs with tRNA anticodon UAC
Initiator tRNA binds to P site on ribosome at the START codon
“A” site on ribosome is ready for tRNA carrying next amino acid

32. Met Met Large ribosomal subunit Initiator tRNA P site A site Start
Met
Met
Large
ribosomal
subunit
Initiator tRNA
P site
A site
Start
codon
mRNA
Small ribosomal
subunit 1 2

33. Translation Continued
2. Elongation
Adding amino acids to the polypeptide chain
tRNA carries next amino acid in to the A site
Peptide chain is transferred (translocation) to amino acid in A site
Then the polypeptide chain in A site slides over to the P site
New codon on A site is ready to receive next tRNA

34. Amino
acid
Polypeptide
P site
A site
Anticodon
mRNA
Codons 1
Codon recognition
mRNA
movement
Stop
codon 2
Peptide bond
formation
New
peptide
bond 3
Translocation

35. Translation Finished 3. Termination
Ribosome comes to stop codon (UAA, UGA, or UAG)
Release factor binds to A site
Ribosome separates into its two subunits
Polypeptide is released

36. polypeptide synthesis
Transcription
DNA
mRNA is transcribed
from a DNA template. 1
mRNA
RNA
polymerase
Amino acid
Translation
Each amino acid
attaches to its proper
tRNA with the help of a
specific enzyme and
ATP. 2
Enzyme
ATP
tRNA
Anticodon
Initiator
tRNA
Large
ribosomal
subunit
Initiation of
polypeptide synthesis 3
The mRNA, the first
tRNA, and the ribosomal
sub-units come together.
Start Codon
Small
ribosomal
subunit
mRNA

37. to the polypeptide chain as the mRNA is moved through the ribosome,
New peptide
bond forming
Growing
polypeptide 4
Elongation
A succession of tRNAs
add their amino acids
to the polypeptide chain
as the mRNA is moved
through the ribosome,
one codon at a time.
Codons
mRNA
Polypeptide 5
Termination
The ribosome
recognizes a stop
codon. The polypeptide
is terminated and
released.
Stop codon