Chapter 12- DNA Flashcards
(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
Frederick Griffith-1928
Studied how bacteria makes people sick
Harmless r-strain + mouse (Frederick Griffith-1928)
Living mouse
Harmful s-strain + mouse (Frederick Griffith-1928)
Dead mouse
Heat-killed S-strain + mouse (Frederick Griffith-1928)
Living mouse
Heat-killed s-strain + r-strain (Frederick Griffith-1928)
Dead mouse
Something transferred from the dead S to the R – the genes = “transformation”
Oswald Avery- 1944
Studied what transferred in griffith’s experiment
(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
(Oswald Avery- 1944) transformation factor
Only denaturing DNA stopped transformation = DNA was transforming factor
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
(Alfred Hershey and Martha Chase- 1952) methods of experimenting
Radioactively tagged protein coat and DNA of the virus
Coat: sulfur-35
DNA: phosphorous-32
(Alfred Hershey and Martha Chase- 1952) conclusions
The infected bacteria had P-32; so it was DNA that transferred
Role of DNA
Storing information
Copying information
Transmitting information
Components of DNA
made up of a string of nucleotides that are held by covalent bonds
DNA nucleotides
Has 3 parts:
5- carbon sugar (deoxyribose)
Phosphate group
Nitrogenous base (either adenine, thymine, guanine, or cytosine)
(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
