dna function

What is the basic structure of DNA?

DNA is a nucleic acid made of long chains of nucleotides, each consisting of a phosphate group, deoxyribose sugar, and a nitrogen-containing base.

What are the four types of nitrogenous bases in DNA?

The four types are pyrimidines Thymine (T) and Cytosine (C); and purines Adenine (A) and Guanine (G).

What is the orientation of DNA strands?

double stranded helix where the DNA strands are antiparallel, meaning they run side by side in opposite directions.

5’ end has a free phosphate group and the 3’ has a free hydroxyl group (free sugar)

What are the pairs of complementary bases in DNA?

Thymine pairs with Adenine (2 hydrogen bonds), and Cytosine pairs with Guanine (3 hydrogen bonds).

only purine-pyrimidine pairs fit inside double helix

structure of the dna helix

1) one turn of the helix occurred every ten base pairs

2) negatively charged phosphates faced out

there is a major groove from 3’ down to 5’ and a minor groove 5’ to 3’

charge of histones

positive

DNA vs RNA

DNA:

1) double stranded sugar phosphate

2) deoxyribose sugar which has one OH

3) thymine which has H3C group

RNA:

1) usually single-stranded sugar phosphate

2) ribose sugar which has two OH groups

3) uracil which has no H3C group

How long can DNA from a single diploid human cell extend?

It can extend to almost 2 meters long!

What is the Central Dogma of Biology?

The Central Dogma describes the flow of genetic information from DNA to RNA to proteins.

dna replication → transcription creates rna→ rna translation to create protein

What initiates DNA replication?

Replication is initiated at the origin of replication where a replication bubble is formed.

each bubble has two replication forks

basic steps of dna replication

1) replication begins at specific sites where the two parental strands separate and form replication bubbles

2) the bubbles expand laterally, as DNA replication proceeds in both directions

3) eventually, the replication bubbles fuse and the synthesis of the daughter strands is complete

replication begins at many sites along molecule in eukaryotes

conservation of DNA replication

semi conservative as one strand from parental DNA while other strand is the newly synthesized daughter cell

mechanisms of dna replication

1) initial nucleotide strand is an rna primer, rna primate wich synthesizes primer on dna strand

2) dna replication catalyzed by dna polymerase iii which needs an rna primer

3) dna polymerase i replaced rna primer with dna nucleotides

4) dna polymerases add nucleotides to 3’bend of growing strand (synthesis of new strand is 5’ to 3’) (reads template strand 3’to 5’)

proteins for dna replication

1) dna helicases unwind the double helix by breaking hrdrohen bonds between the strands

2) single stranded dna binding proteins prevent dna strands from rejoining after helicase separates strands

3)dna polymerase iii extends the strand from primer in the 5’ to 3’ directio and has proof reading ability

4) dna polymerase i degrades rna primers and replaces with dna nucleotides synthesized in 5’ to 3’ directio. and has proof reading activity

5) dna ligase joined the short dna fragments on lagging strand (okazaki fragments) into a continuous daughter strand (introduces a phosphodiester bond between two fragments)

6) topoisonerase binds dna and relieve torsional stress experiences further upstream along helix that courts as a result of unwinding due to helicase activity by cutting phosphodieister bond from one or both strands of double helix to relax, and then cut strands are reabbealed)

What is the role of DNA polymerase I?

DNA polymerase I replaces RNA primers with DNA nucleotides during replication.

What did Frederick Griffith discover?

He discovered that the pneumococcus bacterium could transform from one strain to another, suggesting the presence of a 'transforming factor'.

non-encapsulated vs encapsulated

encapsulated will infect while non will not

oswald avery

american bacteriologist who performed experiment using cultures to identify specific molecule s that could transform non encapsulated bacterium into capsulated form

use do cultures to transform bacteria gave better control than mice.

oswald avery conclusion

transforming substances is dna, conclusion based on experimental evidence that only dna worked in transforming harmless bacteria into virulent bacteria

many were skeptical as little was known abt dna and scientific opinion still favoured protein as hereditary material at the time

What conclusion did the Hershey-Chase experiment reach?

It concluded that DNA is the genetic material, as DNA was found in the bacterial pellet after phage infection.

rosalind franklin

british chemist took Xray diffraction photo of dna, playing critical role in identifying dna structure

distinctive x in xray photo is a telltale pattern of a helix

watson and crick

dna consists of two separate dna polymers called strands and these two strands are twisted around eachother to form a double helix.

original three postulated mechanism of dna replication

semi-conservative, conservative, dispersive

meselson/stahl experiment conclusion

dna relplication in e. coli is semi-conservative