what is the central Dogma.
DNA—RNA—Protein
BOOK!
what does the genetic material need to be:
- Able to store lots of information.
- Stable.
- Inheritable.
- Able to be replicated.
what is DNA?
what can it also be referred to as?
DNA is a polymer - is a chain of nucleotides, more specifically a chain of nucleoside monophosphates (NMPs). It is also referred to as a polynucleotide
what is the monomer/basic unit of DNA.
How do they link?
what do they form?
Nucleotides
- linked by phosphodiester bods
-linked together to form a polynucleotide chain.
what are the components of DNA-each NMP
Each nucleoside monophosphate (NMP) consists of a :
- a Base
- a Sugar
- one phosphate group
Display formula of deoxyribose
Book
what are the 4 nitrogenous bases;
Adenosine (C5H5N5)
Guanine (C5H5N5O)
(Purines= double ring)
Cytosine (C4H5N3O)
Thymine (C5H6N2O2)
(Pyrimidines= single ring)
Diagrams of nitrogenous bases.
BOOK
How is the base attached to the sugar?
By B-N-glycosidic bond attached to nitrogen number 1 of the pyrimidine base (C and T) or number 9 of the purine base (A and G).
how is Nucleoside converted into a nucleotide?
By attachment of a phosphate group to the 5 carbon of the sugar. Up to 3 different phosphates can be attached in series.
What’s the role of the phosphate group in DNA (2)
How is it formed?
The phosphate group helps to form the backbone of the DNA molecule which provides structural integrity and a framework for the double helix.
The phosphate group attached to the 5’ carbon of the sugar in one nucleotide forms a bond /links with the hydroxyl group on the 3’ carbon of the sugar in the next nucleotide. This strong 3’-5’ phosphodiester bond creates a continuous chain.
What are the full names of the 4 different nucleotides that polymerise to form DNA are:
BOOK FOR MORE INFORMATION
*polymerise =combine or cause to combine to form a polymer:
2’-deoxyadenosine 5’-triphospahte (DATP)
2’-deoxyguanosine 5’-triphospahte (DGTP)
2’-deoxycytidine 5’-triphospahte (DCTP)
2’-deoxythymidine 5’-triophospahte (DTTP)
Discovering the helix.
Prior to 1953, it was assumed that DNA was made up of just one strand/one polymer.
In 1951, Linus Pauling published that proteins/peptides could form α-helices.
Rosalind Franklin and PhD student Raymond Gosling (KCL) used X-ray diffraction to
confirm that DNA also formed an α-helix (photo taken on 1952, published on 1953).
what is DNA made up of?
- Double helix
- Antiparallel Strands
- 5 and 3 Ends
- Base Pairing and Sequence Direction
- Hydrogen Bonds
- Sugar Phosphate Backbone.
- DNA is made up of two chains of nucleotides twisted into a double helix. Each chain (or strand) is a polymer of nucleoside monophosphates (NMPs).
- These two strands run in
opposite directions – antiparallel- One strand runs from the 5’ to 3’ direction, and the complementary strand runs from the 3’ to 5’ direction. This arrangements enables the strands to complement each other, allowing twice the amount of information to be stored in one DNA molecule). - The 5’ end has the free phosphate group on the 5th carbon.
- The 3’ end has a free OH- group on the 3rd carbon.
- complementary bases = A-T, C-G via hydrogen bonds).
5’-ATCG-3’- the direction of the strand . This ensures accurate replication and transcription of genetic information. - The base pairs are held together by hydrogen bonds.
A-T = 2 hydrogen bonds
C-G= 3 hydrogen bonds. - Alternating sugar (deoxyribose) and phosphate groups make the backbone of each strand.
DNA strands are intertwined. what do the twisting of helix create.
Spaces known as major and minor groove.
MAJOR:
- Wider
- 22 A (angstroms) wide.
-where proteins, such as transcription factors and DNA-binding proteins, interact with the DNA. This is because the larger width allows for more accessible interaction with the nitrogenous bases, providing specific binding sites.
MINOR
- narrow
- 12 A wide
- Although it is less accessible than the major groove, the minor groove can also be a site for protein binding, but with different specificity. Some small molecules and drugs can bind here as well.
The stability of DNA is primarily attributed to two key types of bonds:
Phosphodiester Bonds
Structure: These are covalent bonds formed between the phosphate group of one nucleotide and the sugar of the next nucleotide in the DNA strand.
Stability: These strong covalent bonds create a strong backbone for DNA, making it resistant to breakage and ensuring the integrity of the genetic information during replication and transcription.
Hydrogen Bonds
Base Pairing: The nitrogenous bases (A, T, C, G) on opposite strands of DNA are held together by hydrogen bonds:
- Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds.
- Cytosine (C) pairs with Guanine (G) via 3 hydrogen bonds.
Stability: while these bonds are individually weak, collectively they provide stability and flexibility for the DNA double helix. The specific base pairing also ensures accurate replication and transcription.
What are the different conformations of the DNA double helix.
B-DNA (most common)
A-DNA
Z-DNA
TABLE IN BOOK.
What property of DNA structure allows it to store lots of information?
base pairing
Which properties of DNA allows it to be stable? 2
Sugar-phosphate backbone
Hydrogen bonds
Which property of DNA allows it to be easily replicated?
Directionality
