1. DNA, RNA, and Protein Synthesis
Chapter 10
DNA, RNA, and Protein Synthesis
SPI Identify the structure and function of DNA.
SPI Associate the process of DNA replication with its biological significance.
SPI Recognize the interactions between DNA and RNA during protein synthesis.

2. The History of DNA
Fredrick Griffith (1928) working with Streptococcus pneumoniae conducted transformation experiments of virulent & nonvirulent bacterial strains
Oswald Avery (1949) showed that DNA, not protein or RNA, was responsible for the transformation seen in Griffith’s experiments
Hershey & Chase (1952) used bacteriophages (viruses) to show that DNA, not protein, was the cell’s hereditary material
Rosalind Franklin (1951) used x-rays to photograph DNA crystals
Erwin Chargaff (1950) determined that the amount of A=T and amount of C=G in DNA; called Chargaff’s Rule
Watson & Crick (1953) discovered double helix shape of DNA (A pairs with T; C pairs with G) & built the 1st model

3. Griffith’s Experiments
In 1928, Fredrick Griffith was studying the bacteria (S. pneumoniae) that cause pneumonia. - Smooth strain (virulent)  Mouse dies - Rough strain (non-virulent)  Mouse lives - Heat-killed smooth strain  Mouse lives - Heath-killed smooth + rough strains  Mouse dies

4. Griffith’s Experiments
Heat-killed, disease-causing bacteria (smooth colonies)
Harmless bacteria (rough colonies)
Control (no growth)
Harmless bacteria (rough colonies)
Heat-killed, disease-causing bacteria (smooth colonies)
Disease-causing bacteria (smooth colonies)
Dies of pneumonia
Dies of pneumonia
Lives
Lives
Live, disease-causing bacteria (smooth colonies)

5. Griffith’s Experiments
Griffith called this process transformation: one type of bacteria turned into another
ex. Rough strain turned into smooth strain when the two were mixed
Through additional experiments, Oswald Avery concluded that DNA, not RNA or protein, is responsible for transformation in bacteria
Only bacteria with undestroyed DNA could transform other bacteria
Destroyed RNA and protein didn’t make a difference

6. Hershey-Chase Experiments
Hershey and Chase confirmed that DNA, not protein, is the hereditary material by conducting experiments with bacteriophages

7. Watson & Crick
Watson and Crick created a model of DNA by using Rosalind Franklin’s DNA diffraction x-rays
Watson and Crick are associated with the discovery of DNA as a double-helix (two strands wound around each other like a spiral staircase)

8. James Watson
(1928-?)
89-years old
Francis Crick
( )
Rosalind Franklin
( )

9. DNA Structure

10. DNA Structure A DNA nucleotide is made of three components:
5-carbon deoxyribose sugar
Phosphate group
One of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T).

11. DNA Structure
The two categories of nitrogenous bases are purines and pyrimidines Purines: Double-ring structure - Adenine (A) and Guanine (G) Pyrimidines: Single-ring structure - Cytosine (C) and Thymine (T)

12. DNA Structure Bonds Hold DNA Together
Nucleotides along each DNA strand are linked by covalent bonds
Complementary nitrogenous bases are bonded by hydrogen bonds
Hydrogen bonding between the complementary base pairs, G-C and A-T, holds the two strands of a DNA molecule together

13. DNA Structure: Antiparallel Strands
One strand of DNA goes from 5’ to 3’
The other strand is opposite in direction, going 3’ to 5’
This will be important to remember when it comes to DNA replication

14. Chargaff’s Rule Base-pairing rules of DNA are known as Chargaff’s Rule
Adenine (A) always pairs with thymine (T)
Guanine (G) always pairs with cytosine (C)
Therefore, in a DNA strand, the % of adenine = % of thymine; % of cytosine = % of guanine
Example: If a particular DNA molecule is 30% adenine, then it is 30% thymine, which equals 60%. This means that the remaining 40% of the molecule is 20% cytosine and 20% guanine.

15. DNA Replication Steps of DNA Replication
DNA has to be copied before a cell divides
DNA is copied during the S or synthesis phase of interphase
New cells will need identical DNA strands
Steps of DNA Replication
Replication begins with the separation of the DNA strands by helicases
To begin process, RNA primase must first add a small primer (sequence of RNA)
Then, DNA polymerases form new strands by adding complementary nucleotides to each of the original strands.

16. DNA Replication Begins at origin of replication
DNA strands are opened (“unzipped”) by helicases
Two strands open, forming replication forks (Y-shaped region)
New strands grow at the forks
DNA polymerase adds complementary nucleotides to new strands
Replication
Fork
Parental DNA Molecule 3’ 5’

17. DNA Replication

18.
DNA Replication
DNA polymerase can only add nucleotides to the 3’ end of the DNA
This causes the NEW strand to be built in a 5’ to 3’ direction
Leading strand (built toward replication fork) completed in one piece
Lagging strand (built moving away from the replication fork) is made in sections called Okazaki fragments
RNA primers are removed and replaced with DNA sequences
DNA ligase joins segments together

19. DNA Replication

20. Errors in DNA Replication
Changes in DNA are called mutations
DNA proofreading and repair prevent many replication errors
Unrepaired mutations that affect genes that control cell division can cause diseases such as cancer

22. RNA: Structure and Function
RNA, like DNA, consists of long chains of nucleotides Three differences between DNA and RNA - The sugar is ribose - Single-stranded - Contains uracil instead of thymine *Base pairings are A-U and C-G

23. DNA vs. RNA

24. RNA: Structure and Function
Types of RNA
Cells have three major types of RNA:
messenger RNA (mRNA): carries the genetic message from nucleus to cytoplasm
ribosomal RNA (rRNA): component of ribosomes
transfer RNA (tRNA): carries amino acids to add to a growing polypeptide (protein) chain

25. Messenger RNA (mRNA) Single, uncoiled, straight strand of nucleic acid
Copies DNA’s instructions in nucleus & carries them to the ribosomes in cytoplasm where proteins can be made
mRNA’s base sequence is translated into the amino acid sequence of a protein
Three consecutive bases on mRNA called a codon (e.g. UAA, CGC, AGU)
Reusable

26. Ribosomal RNA (rRNA)
rRNA & protein make up the large and small subunits of ribosomes
Globular shape
Ribosomes are the sites of translation (the making of proteins)

27. Transfer RNA (tRNA) Clover-leaf shape (folds up)
Single stranded molecule with attachment site at one end for an amino acid
Opposite end has three nucleotide bases called the anticodon
Anticodon will be complementary to the codons of the mRNA

28. The Central Dogma of Biology
DNA  mRNA  Protein
Nuclear
membrane
Transcription
RNA Processing
Translation
DNA
Pre-mRNA
mRNA
Ribosome
Protein

29. Transcription
Translation

30. TRANSCRIPTION
DNA  mRNA

31. Transcription
During transcription, DNA acts as a template for directing the synthesis of mRNA
Happens IN THE NUCLEUS (know this!)
Transcription: the copying of the DNA into a complementary strand of RNA
- Uses the enzyme RNA polymerase

32. Transcription: Step 1
RNA polymerase, an enzyme, binds to a region of DNA known as the promoter
The promoter is a sequence of DNA that tells transcription where to begin

33. Transcription: Step 2
Multiple enzymes unwind and separate the two DNA strands
The RNA polymerase will use one of the DNA strands as a template from which to build a strand of RNA (the mRNA)

34. Transcription: Step 3
Using one of the DNA strands as a template, RNA polymerase adds nucleotides that are complementary to the DNA strand
G with C, and U with A
This continues until RNA polymerase reaches a DNA sequence known as the terminator/termination signal
RNA polymerase falls off, and the newly-formed mRNA strand is released

35. Transcription Summary

36. Eukaryotic RNA is Modified
Before leaving the nucleus, the mRNA is edited
This is called splicing
Splicing involves removing (cutting out) portions of the mRNA known as introns
The exons are fused together
One end of the mRNA also receives a poly-A tail, and the other end receives a 5’ cap (bases and chemical groups to prevent mRNA destruction)
Remember it this way: the “exons” get to “exit” the nucleus and be translated into proteins! The introns stay “in” the nucleus.

37. TRANSLATION
mRNA  Protein

38. Translation
Translation is the process of decoding the mRNA into a polypeptide chain (protein)
The Genetic Code
The genetic code is read in three letter segments called codons
There are 64 different codon possibilities that code for only 20 amino acids
-AUG is the start codon
-there are 3 stop codons-
UAA, UAG, UGA

40. Translation: Step 1 (Initiation)
Start codon
mRNA travels from the nucleus to the cytoplasm
mRNA attaches to one end of a ribosome; called initiation
tRNAs attach the correct amino acid floating in the cytoplasm to themselves
The tRNA anticodon “reads” & temporarily attaches to the mRNA codon in the ribosome (methionine is the start codon)

41. Translation: Step 2 (Elongation)
5. Two amino acids at a time are linked together by peptide bonds to make polypeptide chains (protein subunits); called elongation

42. Translation: Step 2 (Elongation), cont.
Growing polypeptide chain

43. Translation: Step 3 (Termination)
7. Ribosomes move along the mRNA strand until they reach a stop codon (UAA, UGA, or UAG); called termination
8. tRNA’s break loose from amino acid, leave the ribosome, & return to cytoplasm to pick up another amino acid

44. End Product –The Protein!
The end product of protein synthesis is a primary structure of a protein
A sequence of amino acids bonded together by peptide bonds

45. End Product –The Protein!
The linear, primary structure will fold up into a functional protein
Once the protein is properly folded into a tertiary or quaternary structure, it can perform its job!
STRUCTURE = FUNCTION

46. Example: How Mutations Affect Protein Structure and Function
Sickle-Cell Anemia

47. Example: How Mutations Affect Protein Structure and Function
Cystic Fibrosis
The thick build-up of mucus occurs in the lungs, which affects breathing and can cause recurring respiratory infections
Mucus build-up also occurs in the pancreas, which prevents the normal secretion of necessary digestive enzymes. This can lead to digestive problems and poor growth/development. (Many CF patients are prescribed pancreatic enzymes)