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DNA GRADE 12

LOCATION OF DNA IN A CELL

Locus: Position of gene on chromosome

LOCATION OF DNA IN A CELL

•Chromatin is a complex of DNA and protein, and is found in the

nucleus of eukaryotic cells.•Histones are proteins that are

responsible for the first level of DNA packing in chromatin

•The chromatin network in the nucleus of a cell will coil up

tightly during cell division and form individual chromosomes.

DNA : A LONG LINEAR POLYMER FOUND IN THE NUCLEUS OF A CELL AND FORMED FROM NUCLEOTIDES AND SHAPED LIKE A DOUBLE HELIX ASSOCIATED WITH THE TRANSMISSION OF GENETIC INFORMATION .

THE STRUCTURE OF DNA

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http://cronodon.com/BioTech/Cell_Nucleus.html

NUCLEIC ACID : (BIOCHEMISTRY) ANY OF VARIOUS MACROMOLECULES COMPOSED OF NUCLEOTIDE CHAINS THAT ARE VITAL CONSTITUENTS OF ALL LIVING CELLS.

TYPE OF NUCLEIC ACID :

DNA AND RNA

STRUCTURE OF A NUCLEOTIDE

A nucleotide is made of 3 components:

• A Pentose sugar

• This is a 5 carbon sugar

• The sugar in RNA is ribose.

• The sugar in DNA is deoxyribose.

STRUCTURE OF A NUCLEOTIDE

• A Phosphate group

• Phosphate groups are important because they link the sugar on one nucleotide onto the phosphate of the next nucleotide to make a polynucleotide.

STRUCTURE OF A NUCLEOTIDE• A Nitogenous base

• In DNA the four bases are:• Thymine• Adenine• Cytosine• Guanine

• In RNA the four bases are:• Uracil• Adenine• Cytosine• Guanine

WHAT IS DNA• A nucleic acid that contains genetic

information.

• Double helix shape

• Composed of nitrogenous bases (adenine, cytosine, guanine and thymine), a five-carbon sugar (deoxyribose), and a phosphate molecule.

Saturday, April 8, 2023

SUGAR PHOSPHATE BONDS (BACKBONE OF DNA)

• Nucleotides are connected to each other via the phosphate on one nucleotide and the sugar on the next nucleotide

• A Polynucleotide


NITROGENOUS BASES – TWO TYPES

Pyramidines

Thymine - T

Cytosine - C

Uracil - U

Purines

Adenine - A

Guanine - G

ADENINE


GUANINE

COMPLEMENTARY BASE PAIRING

Purines Pyramidines

Adenine Thymine

Adenine Uracil

Guanine Cytosine


BASE PAIRING

• The Nitrogenous Bases pair up with other bases. For example the bases of one strand of DNA base pair with the bases on the opposite strand of the DNA.

THE RULE:• Adenine always base pairs with Thymine (or Uracil if RNA)

• Cytosine always base pairs with Guanine.

• This is beacuse there is exactly enough room for one purine and one pyramide base between the two polynucleotide strands of DNA.

3.DISCOVERY OF THE DNA STRUCTURE

•Early in the 20th century, the identifi-cation of the molecules of inheritance

loomed as a major challenge to biologists.

•Discovery of the genetic role of DNA began with research by Frederick Griffith in 1928.

•Griffith worked with 2 strains of a bacterium, 1 pathogenic (S cells) & 1 harmless (R cells)

•Heat-killed pathogenic strain were mixed with living cells of harmless strain and the result = some living cells

became pathogenic.•This phenomenon was called transformation, now defined

as a change in genotype & phenotype due to assimilation of foreign DNA.

1952 :A. Hershey & M. Chase experiments showing that DNA is the genetic material of T2 phage.

To determine the source of genetic material in the phage, they designed an experiment

showing that only 1 / 2 components of T2 (DNA or

protein) enters an E. coli cell during infection

They concluded that the injected DNA of the phage provides the

genetic information

4 .THE ROLE OF DNA

•DNA is vital for all living beings – even plants .

•It is important for:• inheritance ,•coding for proteins and •the genetic instruction

guide for life and its processes .

DNA holds the instructions for an organism's or each cell’s

development and reproduction and ultimately death.

DNA can replicate itself.

NON-CODING DNAMulticellular eukaryotes have many introns(non-

coding DNA) within genes and noncoding DNA between genes.

The bulk of most eukaryotic genomes consists of noncoding DNA sequences, often described in the

past as “junk DNA”Much evidence indicates that noncoding DNA

plays important roles in the cell.Sequencing of the human genome reveals that

98.5% does not code for proteins, rRNAs, or tRNAs.

DNA REPLICATION

DNA replication is a biological process that occurs in all living organisms and copies their exact DNA. It is the basis for biological inheritance.


DNA: REPLICATION

The first major step for the DNA Replication to take place is the breaking of hydrogen bonds between bases of the two antiparallel strands.

The unwounding of the two strands is the starting point. The splitting happens in places of the chains which are rich in A-T. That is because there are only two bonds between Adenine and Thymine (there are three hydrogen bonds between Cytosine and Guanine).

Helicase is the enzyme that splits the two strands. The structure that is created is known as "Replication Fork".

DNA UNWINDS…..


Origins initiate replication at different times.


REPLICATION FORK

The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA.

These two strands serve as the template for the leading and lagging strands, which will be created as DNA polymerase matches complementary nucleotides to the templates; The templates may be properly referred to as the leading strand template and the lagging strand template

DNA strands have a directionality, and the different ends of a single strand are called the"3' (three-prime) end" and the "5' (five-prime) end" with the direction of the naming going 5 prime to the 3 prime region.

The strands of the helix are anti-parallel with one being 5 prime to 3 then the oppositestrand 3 prime to 5.

These terms refer to the carbon atom in deoxyribose to which the next phosphate in the chain attaches. Directionality has consequences in DNA synthesis, because DNA polymerase can synthesize DNA in only one direction by adding nucleotides to the 3' end of a DNA strand.

REFERENCES

• http://www.slideshare.net/guest93618/dna-981508?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=qf1&b=&from_search=35\. Accessed on the 06 March 2014

• http://www.slideshare.net/lissyjyothish/dna-9042838?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=qf1&b=&from_search=25. accessed on the 06 March 2014

• http://www.slideshare.net/amalaielmorsy/dna-30211742?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=default&b=&from_search=48. Accessed on the 2014

http://www.slideshare.net/guest93618/dna-981508?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=qf1&b=&from_search=35/




http://www.slideshare.net/lissyjyothish/dna-9042838?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=qf1&b=&from_search=25




http://www.slideshare.net/amalaielmorsy/dna-30211742?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=default&b=&from_search=48




• http://www.slideshare.net/aquanat/dna-12598390?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=qf1&b=&from_search=52from_search=66.Accessed on the 06 March 2014

• http://www.slideshare.net/guestd6e7b3/dna-presentation-910904?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=default&b=&from_search=66.Accessed on the 06 March 2014

http://www.slideshare.net/aquanat/dna-12598390?qid=56427ae3-eee5-4740-a362-2a25b50f7354&v=qf1&b=&from_search=52




• LINK TO MY SLIDE SHARE ACOOUNT

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