1. DNA, RNA, & Protein Synthesis
DNA & Genes Chapter 11
DNA, RNA, & Protein Synthesis

2. DNA Molecule of Heredity A. Structure
DNA (polymer) is a long molecule made up of Nucleotides (monomers)
A Nucleotide consists of:
Deoxyribose (a 5-carbon sugar)
a phosphate group
One of 4 Nitrogenous bases (contain nitrogen)
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
PURINES
PYRIMIDINES
The nitrogenous bases of DNA (purines – double ring / pyrimidines single ring)

3. Structure of DNA (cont.)
DNA is like a twisted ladder:
Rungs: complementary base pairs (A=T, G=C)
Uprights: deoxyribose and phosphate groups
Your Turn: Match this DNA base sequence with its correct complementary DNA bases:
T-C-G-A-A-C-T
A-G-C-T-T-G-A

4. B. History
1. CHARGAFF (1949): discovered that the % of Cytosine and Guanine were about the same in DNA; the same was true about Adenine and Thymine
This suggests BASE PAIRING……….. that C bonds with G and A bonds with T!
Source of DNA A T G C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8

5. History (cont.)
2. Wilkins and Franklin(1952): took X-Ray photographs of DNA which suggested a twisted, helical structure, 2 strands, and bases in the center
3. Watson and Crick (1953): using all the research to date, discovered the structure for DNA: A DOUBLE HELIX (with sugar-phosphate backbones and bases on the inside held together by H bonds)

6. C. DNA Replication: making more DNA during the S Phase of the Cell Cycle (in the nucleus)
1. The enzyme helicase unwinds DNA double helix (breaks hydrogen bonds btwn. bases) & a replication fork is created.
(Each old DNA strand will act as a template for 2 new strands to be added on)
2. Enzyme called DNA Polymerase binds to replication fork and adds free nucleotides to each old strand of DNA
3. DNA Polymerase remains attached until 2 new DNA strands are created; it “proofreads” the strands to minimize error in the process.

7. DNA Replication (cont.)
Diagram of DNA Replication:

8. DNA  Protein RNA: Ribonucleic Acid Used to make proteins
Single-stranded polymer made up of nucleotides.
RNA Monomer (Nucleotide) is made of -
Ribose (5 C sugar) + Phosphate group + N Base
Cytosine (C)
Guanine (G)
Adenine (A)
Uracil (U) – NO THYMINE in RNA!

9. Types of RNA 3 types of RNA: 1. messenger RNA (mRNA) – single stranded
transmits info from DNA to protein syn.
2. transfer RNA (tRNA) - single stranded/
20 or more varieties ea. w/ ability to bond to only
1 specific AA
3. ribosomal RNA (rRNA) – globular / major
component of ribosome

10. Protein Synthesis (overview)
2 Stages in making proteins:
Transcription – using DNA template to make mRNA strand
Translation – using mRNA strand to create polypeptides
DNA
RNA
Protein
Transcription
Translation

11. 1. Transcription
The Goal of Transcription is to produce a single-stranded mRNA helix that contains information from DNA to make proteins
How it’s done: (This happens in the Nucleus!)
1. DNA strand unwinds/unzips complementary DNA strands
2. Enzyme called RNA Polymerase binds to DNA “promoter” regions and “plugs in” complementary RNA nucleotides to the DNA template.
Example = DNA Template: ATTGGCAGT
new RNA Strand: UAACCGUCA

12. Transcription (cont.)

13. Transcription (cont.)
3. Once produced, this pre-mRNA strand breaks away when RNA polymerase reaches a sequence of bases on DNA that act as a stop sign.
The finished product (mRNA) moves out of the Nucleus through a nuclear pore into the cytoplasm.
4. 2 DNA complementary strands rejoin

14. 2. The Genetic Code How do we get proteins from mRNA strands?
The mRNA strand must be read in groups of 3 nucleotides, called a CODON.
Different Codons translate for different Amino acids.

15. Codons in mRNA

16. Codons in mRNA “Start” codon = AUG (Methionine)
“Stop” codons = UAA, UAG, and UGA
Example:
mRNA Strand:
U-C-A-U-G-G-G-C-A-C-A-U-G-C-U-U-U-U-G-A-G
methionine glycine threonine cysteine phenylalanine STOP

17. 3. Translation
The Goal of Translation is to “translate” these mRNA codons into their amino acids to form a polypeptide.
How it’s done:
1. mRNA strand attaches to a ribosome (rRNA)
2. Each mRNA codon passes through ribosome
3. Free-floating Amino Acids from cytosol are brought to ribosome by tRNA
4. Each tRNA has an anticodon to match up to mRNA codons
5. Amino Acids are joined as tRNA keeps bringing them
6. Polypeptide chain grows until “stop” codon is reached

18. Translation (cont.)
Translation

19. Genetic Changes: Mutations A. Types of Mutations
1. Gene Mutations: changes in nucleotides
Point Mutations or Frameshift Mutations
2. Chromosome Mutations: changes in # or structure of chromosome
Deletion
Insertion/Duplication
Inversion
Translocation

20. 1. Gene Mutations
a. Point Mutation: the substitution, addition or removal of a single nucleotide
b. Frameshift Mutations: types of point mutations that shift the “reading frame” of the genetic message

21. B. Chromosome Mutations
1. Deletion……………………………
2. Insertion/Duplication…………
3. Inversion…………………………
4. Translocation…………………….

22. Reproductive vs. Body Cell Mutations
Reproductive Cells – Mutations when multiplied become the genetic makeup of the new offspring.
Body Cells – Ultraviolet Radiation, affects the cell of the individual. Not passed on, but can cause harm to individual. (Mutagens)

23. Are all mutations bad? No!
Positive Mutations are often called adaptations.
These adaptations are beneficial to the species if they become a predominant part of the gene pool.

24. Homework In your book page. 306 Mini-Lab 11-2
Complete the procedure and answer questions 1-3.
Quiz Thursday on DNA, Replication, Protein Synthesis, and Mutations

25. Gene Regulation in Prokaryotes
The lac operon enables the production of lactose-processing enzymes in E. coli, but only when needed.
In the absence of lactose, the repressor protein binds to the operator on DNA and inhibits transcription of lactose-processing enzymes.
In the presence of lactose, the repressor is inhibited from binding with the operator; this all ows transcription to take place to produce lactose-processing enzymes.