Biology; DNA History/ Structure
Reasons for accuracy
-DNA polymerase self checks and corrects mismatched pairs
Result of DNA replication
-Each new DNA molecule = one new strand and one original strand from the starting molecule -Two strands of DNA that are identical to each other
Error rate
1 in 1 billion base pairs About 3 mistakes each time our DNA is replicated
There are _____ kinds of nitrogenous bases
4
DNA Repair Enzymes
A family of enzymes that checks and corrects DNA.
The difference between a nucleotide and a nucleoside
A nucleoside has two parts: a pentagonal sugar (deoxyribose) and a nitrogenous base (in color). When a nucleoside is joined to a phosphate, it is called a nucleotide.
What do nucleotides form?
A nucleotide consists of three things: A nitrogenous base, which can be either adenine, guanine, cytosine, or thymine (in the case of RNA, thymine is replaced by uracil). A five-carbon sugar, called deoxyribose because it is lacking an oxygen group on one of its carbons. One or more phosphate groups.
Purines
Adenine and Guanine
What do phosphate groups do?
Along with sugars and bases, it makes up nucleic acids, like DNA and RNA. As part of energy carriers, like ATP, it provides energy for moving our muscles.
Avery
Avery--1944 Discovered that DNA is the nucleic acid that stores and transmits genetic information from parents to offspring Backed up Griffith's experiments with this info.
Chargaff's Rules
Chargaff discovered how the nitrogenous bases bond together Adenine always bonds with Thymine Guanine always bonds with Cytosine
Step 2
Complimentary bases are added to the strands by enzymes called DNA polymerases Ex - a strand of DNA with the bases ATTCGAG would have a complimentary strand of TAAGCTC
Pyrmidines
Cytosine and Thymine
In prokaryotes...
DNA molecules are located in the cytoplasm of the cell
DNA length
DNA must be wrapped tightly to fit into cells Imagine fitting 900 yards (300m) of rope into a backpack
Chromosomes
DNA wound tightly around proteins called histones
When does DNA replication occur?
During the S phase of the cell cycle - before mitosis
On the way to DNA timeline
Griffith, Avery, Chargaff, Rosalind Franklin and Maurice Wilkins, Hershey-Chase, Watson and Crick
Griffith
Griffith--1928 -Experimented on mice -Observed that some harmless strains of bacteria could change into harmful strains (he called this transformation) -Why? There is some kind of "genetic material" being passed from one to the other!
Hershey-Chase
Hershey-Chase--1952 Concluded that the genetic material in a virus was DNA not proteins
DNA replication produces...
It produces two new complimentary strands following the rules of base pairing (Chargaff Rules)
Why is DNA replication necessary?
Need copies of the DNA, so that after mitosis the new cells are identical to the original cell.
What is DNA replication?
Process of copying the DNA, by using the original DNA as a template.
Rosalind Franklin and Maurice Wilkins
Rosalind Franklin and Maurice Wilkins—1950s Used X-ray diffraction to get information about the structure of DNA The x-ray did not show the structure, but gave important clues The strands are twisted around each other There are 2 strands
Structure of DNA
The backbone of DNA is formed by sugar and phosphate groups of the nucleotide The nitrogenous bases stick out from the sides and can be joined together in any order so any sequence of bases is possible
Step 1 of DNA replication
The enzyme, DNA Helicase unzips the original DNA. -Breaks H-bonds holding bases together -Creates two separate strands that are used as a template for copying DNA (The area where the double helix separates is called the replication fork)
What makes up the "rungs" of the DNA molecule?
The nitrogenous bases
Watson & Crick
Watson & Crick--1953 created the double helix model for DNA Clues from Franklin's X-ray helped them explain their model
Each nucleotide is made up of three parts...
a 5-carbon sugar called deoxyribose a phosphate group and a nitrogenous base (Nitrogen Containing)
DNA replication is carried out by many ____________
enzymes
Many _______ have ____ times as much DNA as ______
eukaryotes, 1000 times, prokaryotes
Most prokaryotic DNA...
is a single circular molecule that contains nearly all the cell's genetic information
DNA location in Eukaryotes
located in the nucleus in the form of chromosomes
DNA
long molecule made of nucleotides
What makes up the sides of the DNA molecule?
phosphates
They are divided into two classes...
purines and pyrmidines
Each strand of double helix of DNA serves as a _____________ for the new strand
template, or model,
During DNA replication...
the DNA molecule separates into two strands
Humans DNA length
~ 6 billion base pairs It is about 4 cm in length Sounds small, but the cell is only 3.0 µm in diameter (smaller than the length of the DNA)
