1. Chapter 10 DNA, RNA, & Protein Synthesis

2. Watson & Crick During the 1950’s James Watson – American Biologist
Francis Crick – British Graduate Student
tried to determine the structure of DNA
1953: they came up with the structure
- DNA is made up of 2 strands
- double helix shape
- they relied on other scientists to develop their DNA model

3. Wilkins & Franklin
Maurice Wilkins – English physicist and molecular biologist
Rosalind Franklin - British biophysicist, physicist, chemist, biologist and X-ray crystallographer
- took X-ray diffraction photographers of DNA crystals

4. Chargaff In 1949 Erwin Chargaff – American Chemist
discovered the key that lead to the understanding of DNA structure
same amount of A as T
same amount of G as C
was key because it means that there is base pairing
Pyrimidine = contains single ring (T & C)
Purine = contains double ring (A & G)

5. Nobel Prize Winners IN 1962 James Watson Francis Crick Maurice Wilkins
Why not Rosalind Franklin?
Franklin died in 1958 and could not receive the award, only the living can get a Nobel Prize

6. Replication Complementary base pairs allow for:
hydrogen bonds that help hold the 2 strands of DNA molecule together
helps explain how DNA replicates before a cell divides (one strand can serve as a template for making a new complementary strand)

8. What is DNA replication?
DNA replication = process by which DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission

9. What basically occurs?
The two nucleotide strands of the original double helix separate along the strands.
Each strand serves as a template to make new complementary strands.
After replication
-2 identical double stranded DNA molecules separate and move to new cells formed during cell division.

11. Steps of Replication helicases = enzymes that separate the DNA strands
- Helicases move along DNA molecule, breaking hydrogen bonds, allowing the 2 strands of DNA helix to split

12. Steps of Replication
2. DNA polymerase = enzymes that add complementary nucleotides to each of the original strands
- they are free floating in nucleus
- hydrogen bonds are formed

13. Steps of Replication
3. DNA polymerases finish replicating the DNA and fall off, resulting in 2 separate and identical DNA molecules that are ready to move to new cells during cell division

14. Semi-Conserative Replication
- 1 strand is new and 1 strand is the original
- each (combination) kept (conserved) one of the 2 original strands
Replication occurs in many locations otherwise it would take 53 days to replicate
DNA ligase = enzyme that joins the gaps

15. What about errors?
only about 1 error occurs for every billion of paired nucleotides added
DNA polymerases have repair enzymes that “proof read” DNA
example: a friend might check your term paper for spelling errors
DNA example: if A pairs with a C instead of T, the repair enzymes would fix error by removing C

16. What happens if error is not corrected?
Mutation = a change in the nucleotide sequence of a DNA molecule
= can have serious effects on the function of an important gene and disrupt an important cell function
some DNA can be damaged from chemicals and UV radiation from the sun
some mutations can lead to cancer
explains how mutations can arise and lead to altered cells and organisms
changes allow individuals to survive and reproduce better, so these variations increase in the population over many generations

17. RNA vs DNA RiboNucleic Acid DeoxyriboNucleic Acid
contains sugar ribose
contains nitrogenous bases uracil (U), cytosine (C), guanine (G), and adenine (A)
single stranded
shorter in length
contains deoxyribose
contains nitrogenous bases thymine (T), cytosine (C), guanine (G), and adenine (A)
double stranded
longer in length

19. Types of RNA each type plays a different role in protein synthesis
1. messenger RNA (mRNA) – single stranded RNA molecules that carries the instructions from a gene to make a protein
2. ribosomal RNA (rRNA) – part of the structure of ribosomes; ribosomes made of rRNA’s & many proteins
3. transfer RNA (tRNA) – transfers amino acids to the ribosome to make a protein

20. Flow of Genetic Information
transcription
translation
protein synthesis

21. Transcription trans = “across” scribere = “to write”
process by which the genetic instructions in a specific gene are transcribed or “rewritten” into an RNA molecule
DNA acts as a template for the synthesis of RNA
occurs in the nucleus for eukaryotes
occurs in the DNA containing region for prokaryotes

22. Steps of Transcription
1. RNA polymerase – enzyme that catalyzes the formation of RNA on a DNA template; binds to a promoter
promoter = a specific nucleotide sequence of DNA where RNA polymerase binds & initiates transcription
- after RNA polymerase binds to the promoter, DNA strands unwind & separate

23. Steps of Transcription
2. RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on one DNA strand
the resulting chain is an RNA molecule
complementary base pairing determines the nucleotide sequence in the newly made RNA
FOR EXAMPLE
DNA strand: ATCGAC
RNA strand: UAGCUG
transcription uses only a specific region (a gene) on one of the 2 DNA strands to serve as a template
as RNA polymerase moves past, the separated DNA strands unwind

24. Steps of Transcription
3. RNA polymerase reaches a termination signal
termination signal = specific sequence of nucleotides that marks the end of a gene; a “stop” signal
RNA polymerase releases both the DNA & the newly formed RNA
RNA made during transcription can be one of many types including mRNA, tRNA, or rRNA
newly made RNA can now perform its job in the cell
RNA polymerase can transcribe another gene

26. the next process…
genetic code = term used for the rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid
amino acids are assembled based on instructions encoded in the sequence of nucleotides in the mRNA
3 adjacent nucleotides (letters) in mRNA specify an amino acid (word) in a polypeptide
polypeptide = a chain of amino acids linked together by peptide bonds
codon = each 3-nucleotide sequence in mRNA that encodes an amino acid or signifies a start or stop signal; no codon encodes more than 1 amino acid

27. EX: GCU specifies amino acid ALANINE in genetic code

28. genetic code is nearly universal to all life on Earth & supports the idea that all organisms share an ancient common ancestor
AUG – start codon – a specific sequence of nucleotides in mRNA that indicates where translation should begin
certain sequences of nucleotides in mRNA do not code for amino acids, but instead signals for translation to end
stop codons = UAA, UAG, or UGA

29. Translation translation = the process of making of a protein
instruction for making a protein are copied from DNA to mRNA
Every protein is made of one or more polypeptides
20 different amino acids found in the proteins of living things
amino acid sequence determines how the polypeptides will twist & fold into 3-D structure of the protein
the shape of the protein id critical to its function

30. Steps of Translation
translation or decoding of genetic instructions
(Initiation) 2 ribosomal subunits, tRNA & an mRNA join together
enzymes attach a specific amino acid to one end of each tRNA according to the genetic code
other end of each tRNA contains an anticodon
anticodon = 3 nucleotides on RNA that are complementary to the sequence of a codon in mRNA

31. Steps of Translation 2. (Elongation) polypeptide chain is put together
a tRNA, carrying the appropriate amino acid, pairs its anticodon with the second codon in mRNA
the ribosome then detaches methionine from the first tRNA & peptide bond forms between methionine & second amino acid
the first tRNA then exits the ribosome
the ribosome then moves a distance of one codon along the mRNA

32. Steps of Translation
3. (elongation continued) polypeptide chain continues to grow as the mRNA moves along the ribosome
new tRNA moves in, carrying an amino acid for the next mRNA codon
growing polypeptide chain moves from one tRNA to the amino acid attached to the next tRNA

33. Steps of Translation
4. (termination) polypeptide grows one amino acid at a time
the ribosome reaches the stop codon
newly made peptide falls off

34. Steps of Translation
5. (disassembly) the components of translation come apart
the last tRNA leaves the ribosome and the ribosome moves away from the mRNA
translation machinery is now free to translate the same or another mRNA

39. several ribosomes may translate the same mRNA transcript at the same time
In Eukaryotes – translation of mRNA occurs only after transcription is finished
the new ribosome begins translating mRNA almost as soon as the preceding ribosome has moved aside

40. Human Genome genome = the complete genetic content
biologists have deciphered the order of the 3.2 billion base pairs in the 23 human chromosomes
it would take 10 years to read the total sequence out loud
the challenge now is to learn what information the DNA sequence actually encodes
bioinformatics = new field that uses computers to compare different DNA sequences