Chapter 12- DNA Flashcards by Gail I

(Frederick Griffith-1928) method of experimenting

Isolated harmless r-strain and harmful s-strain
S-smooth colonies of bacteria- caused pneumonia

R- rough colonies of bacteria- harmless

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Frederick Griffith-1928

Studied how bacteria makes people sick

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Harmless r-strain + mouse (Frederick Griffith-1928)

Living mouse

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Harmful s-strain + mouse (Frederick Griffith-1928)

Dead mouse

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Heat-killed S-strain + mouse (Frederick Griffith-1928)

Living mouse

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Heat-killed s-strain + r-strain (Frederick Griffith-1928)

Dead mouse

Something transferred from the dead S to the R – the genes = “transformation”

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Oswald Avery- 1944

Studied what transferred in griffith’s experiment

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(Oswald Avery- 1944) method of experimenting

He denatured (destroyed) different things (carbs, proteins, lipids, RNA) in the bacteria using enzymes

Destroyed one cellular component at a time and examined whether transformation still occurred

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(Oswald Avery- 1944) transformation factor

Only denaturing DNA stopped transformation = DNA was transforming factor

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Alfred Hershey and Martha Chase- 1952

Studied bacteriophages (viruses that infect bacteria) by radioactively tagging a virus as verification of Griffith and Avery’s conclusions

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(Alfred Hershey and Martha Chase- 1952) methods of experimenting

Radioactively tagged protein coat and DNA of the virus
Coat: sulfur-35
DNA: phosphorous-32

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(Alfred Hershey and Martha Chase- 1952) conclusions

The infected bacteria had P-32; so it was DNA that transferred

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Role of DNA

Storing information
Copying information
Transmitting information

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Components of DNA

made up of a string of nucleotides that are held by covalent bonds

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DNA nucleotides

Has 3 parts:
5- carbon sugar (deoxyribose)
Phosphate group
Nitrogenous base (either adenine, thymine, guanine, or cytosine)

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(Finding the structure of DNA) Erwin chargaff’s rule

Percent of adenine is almost equal to percent of thymine

Percent of guanine is almost equal to percent of cytosine

(Finding the structure of DNA) Rosalind Franklin- 1953

Photographed DNA

DNA = dots in rounded x shape

(Finding the structure of DNA) Watson and crick- 1953 (thieves)

Couldn’t create DNA model that fit all roles
Watson saw franklin’s DNA photo
Modeled the double helix structure

Structure of DNA

Two strands
Double helix (twisted ladder)
Antiparallel strands
[A and T] or [G and C] are held together by weak hydrogen bonds (weak bonds= separate easily for copying)
A-T and G-C = base pairing (explains chargaff’s rule)
Each strand can create its complementary strand

Craig venter and Francis Collins- 2000

Analyzed complete human genome

DNA replication

Before a cell divides it copies its DNA in a process called replication and ensures that each daughter cell has the same DNA

DNA replication process

DNA molecule separates, creating replication forks (100s of R.Fs in eukaryotic cells, only 1 R.F in prokaryotic cells because replication occurs in both directions)

DNA replication process part 2

New bases are added by DNA polymerase:

base pairing (a-t and g-c)
creates the complementary strand

Result of DNA replication

2 DNA molecules identical to each other & the original
Each new semi-conservative (conserving one original strand) DNA molecule has:
- one original strand
-one new strand

(Role of enzymes in DNA replication) DNA polymerase

Synthesizes new DNA (reads original strand and attaches new nucleotides) Copies Only works in 5' to 3' direction and so when it has to work in 3' to 5' direction it does it backwards and 3 at a time which results in Okazaki fragments (small chunks of DNA that are copied but not yet linked together) Checks sequence for accuracy

(Role of enzymes in DNA replication) DNA helicase

Unzips DNA (breaks the hydrogen bonds)

(Role of enzymes in DNA replication) DNA ligase

Connects Okazaki fragments

(Role of enzymes in DNA replication) telomerase

Adds telomeres- tips of chromosomes, short repeat DNA segments Extremely difficult to copy Protects important sequences of DNA DNA is safe after repeated replications

(Replication in living cells) during mitosis and meiosis all new cells

Attach regulatory proteins to start s- phase Replicate their DNA Check DNA replication for accuracy Attach new telomeres if needed Create new daughter cells Mitosis ends- 1 original strand & 1 new strand Meiosis ends - either 1 original strand OR 1 new strand

Eukaryotic DNA replication

Spaghetti or x DNA in nucleus Replication starts at hundreds of locations Proceeds in both directions Loose until condensed in prophase

Prokaryotic DNA replication

Circular DNA found in cytoplasm Starts at a single point Proceeds in 2 directions