Chapter 16 & 17 Dna And Protein Synthesis

Front 1

Frederick Griffith

Back 1

Investigated 2 strain of strep:
1. pathogenic
2. harmless
-injected mice with pathogenic = mouse died
-injected with harmless = no effect
-injected with dead pathogenic cells = no effect
-infected with harmless & dead pathogenic = dead
Conclusion : some sort of transformation occured

Front 2

Avery, McCarthy, and Macleod

Back 2

Tested Griffith's theory that either DNA, protein, or RNA was the transforming agent
-only when they allowed DNA to be active, did the transformation occur
*DNA is the transforming agent

Front 3

Erwin Chargaff

Back 3

"Chargaff's Rules"
-DNA from one species to another has different composition (order and amt. of adenine, guanine, cytosine, and thymine)
-the amount of the 4 nitrogenous bases are not all equal but are always present in a characteristic ratio

Front 4

Hershey Chase

Back 4

infected E.coli with T2 bacteriophages in order to determine whether or not DNA or proteins were the transforming agent
Conclusion : DNA is transforming agent

Front 5

Pauling

Back 5

had the idea that DNA was a 3-stranded helical molecule

Front 6

Wilkins & Franklin

Back 6

-took a picture of DNA that led to the realization that DNA was a double helix

Front 7

Watson & Crick

Back 7

discovered that DNA was a double helix based off of Franklin's photo

Front 8

purine and pyrimidines

Back 8

bairs pairs are always purine (long) + pyrimidine (short)
Purines: Adenine and guanine
Pyrimidines: thymine and cytosine
AT : double bond
GC : triple bond

Front 9

Semiconservative Model

Back 9

The Meselson-Stahl experiment tested 3 models
1. conservative
2. semi conservative (accepted)
-2 strand of parental molecule separate and each functions as a template for a new complementary strand
3. dispersive

Front 10

DNA Replication:: Prokaryotes vs. Eukaryotes

Back 10

-Prokaryotes – single chromosome; no nucleus; 5 million base pairs; can quickly replicate – 1 hr.
-Eukaryotes - human – 46 DNA molecules in nucleus; 6 billion base pairs ( 900 AP bio books); very few errors; few hours to replicate

Front 11

Synthesis of leading and lagging strands during DNA replication

Back 11

1. DNA polymerase elongates DNA strands in 5’ – 3’ direction.
2. Leading strand – elongates continuously.
3. Lagging strand – adds short segments - Okazaki fragments
4. Ligase connects the Okazaki fragments

Front 12

Priming DNA synthesis with RNA

Back 12

-DNA polymerase cannot initiate the reaction.
-Primer - a short segment of RNA synthesized by the enzyme primase.
-Each primer is eventually replaced by DNA

Front 13

Summary of DNA Replication

Back 13

1. Helicase unwinds DNA.
2. Proteins stabilize the unwound strand.
3. Leading strand synthesized continuously by DNA polymerase.
4. Lagging strand – Primase adds RNA primer, Okazaki fragments added.
5. Another DNA polymerase replaces RNA primer with DNA.
6. DNA ligase joins the Okazaki fragment to the growing strand.

Front 14

DNA Structure and Features

Back 14

-bases are on interior (hydrophobic)
-double helix
-sugar phosphate backbone on outside
-hydrogen bonds between bases
-covalent bonds hold nucleotides together
-"right-handed" : curves up to the right
-anti-parallel : strands oriented in opposite directions
-1 full turn approx. every 10 base pairs
-van der wahl interactions hold molecules together

Front 15

The two strands of DNA are antiparallel

Back 15

The 5’ to 3’ direction of one strand runs counter to the other strand.
The numbers are assigned to the Carbons of the sugar.

Front 16

helicase

Back 16

unwinds DNA to begin replication

Front 17

topoisomerase

Back 17

relieves the tension before the fork

Front 18

DNA polymerase III

Back 18

elongates DNA strands in 5’ – 3’ direction
-the leading strand is synthesized continuously by DNA polymerase

Front 19

Leading strand vs. Lagging strand

Back 19

leading - DNA is synthesized continuously by DNA polymerase
lagging - DNA can only be synthesized from 5 prime to 3 prime so DNA is added on in fragments (Okazaki fragments)

Front 20

ligase

Back 20

connects the Okazaki fragments

Front 21

primase

Back 21

coordinates the rate of repplication between leading and lagging strands
-DNA polymerase cannot initiate the reaction.
-primase adds a short segment of RNA (primer)
and DNA polymerase takes over from there
-Each primer is eventually replaced by DNA

Front 22

DNA polymerase 1

Back 22

replaces primer with DNA

Front 23

telomere and telomerase

Back 23

the end of strands of DNA with repeating sequences with no genes
-protects the end of the chromosome from deterioration
-During cell division, enzymes that duplicate the chromosome and its DNA cannot continue their duplication all the way to the end of the chromosome
-If cells divided without telomeres, they would lose the ends of their chromosomes, and the necessary information they contain
-The telomeres are disposable buffers blocking the ends of the chromosomes and are consumed during cell division and replenished by an enzyme, the telomerase reverse transcriptase
-telomerase adds RNA that acts like a template for DNA where the telomere is

Front 24

Chargaff's Rules

Back 24

-DNA composition varies from one species to another
And anyone species the amount of four nitrogenous bases are not all equal but are present in a characteristic ratio - molecular diversity

Front 25

Three stages of transcription

Back 25

Initiation
Elongation
Termination

Front 26

Initiation

Back 26

After all and a polymerase binds to the promoter, the DNA strands unwind, and the enzyme initiates RNA synthesis of the start point on the template strand

Front 27

Elongation

Back 27

Polymerase moves downstream unwinding DNA and elongating RNA. The DNA strands then reform a double helix. A single gene can have several polymerases following each other

Front 28

Termination

Back 28

Terminator sequence stops transcription

Front 29

Initiation

Back 29

1. eukaryotic promoters: include a TATA box about 25 nucleotides upstream from the transcriptional start point.
2. transcription factor recognizes the TATA box and binds to DNA before RNA polymerase II
3. additional transcriptional factors join the polymerase on the DNA forming the transcription initiation complex. DNA unwinds and RNA synthesis begins on the template strand

Front 30

the roles of snRNPs and splicosomes in mRNA splicing

Back 30

1. pre-mRNA combines with snRNPs and other proteins to form a spliceosome
2. within spliceosome, base pairs match up at ends of intron
3. RNA transcript is cut to release intron and eons are spliced together