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Background: Nearly every cell in our body contains DNA, which is a very important molecule as it contains important genetic information that tells the cells in your body what to do. Red blood cells are an exception. They do not have nuclei.
The sequence of A, T, G, and C stores information on how to build and run your body. This is why DNA is important.
The DNA structure is known as a "Double Helix."
DNA Double Helix
Deoxyribonucleic acid, known as DNA, is a self-replicating molecule that carries genetic information. All living creatures on the planet have DNA. It is found in the nucleus of nearly all cells in the body.
"Deoxy" means that it is lacking an oxygen atom on "ribose", a type of sugar.
"Nucleic" refers to the fact that this molecule can be found in the nucleus of each cell.
Lastly, the molecule is acidic. DNA is an acid.
Alleles, genes, and chromosomes are made out of DNA.
DNA Structure and Scientists
DNA Structure and Scientists
Francis H. Crick, James D. Watson, and Rosalind Franklin.
In 1952, Rosalind Franklin took a famous X-ray image called Photo 51. This picture showed that DNA has a twisted shape called a double helix. Her clear image helped scientists James Watson and Francis Crick figure out the structure of DNA, which made it much easier to understand how genetic information is stored and passed on.
In 1952, Rosalind Franklin's X-ray diffraction images showed that DNA was a double helix.
James D. Watson, an American biologist, and Francis H. Crick, a British biophysicist, postulated the double helix model in 1953. Rosalind Franklin's photos of DNA were shown to Watson without her approval or knowledge in 1952.
The men received the Nobel Prize. Although Rosalind Franklin’s x-ray data helped reveal the structure of DNA, she did not receive the same recognition at the time.
Nitrogeneous Bases
Nitrogeneous Bases
The following bases make up the rungs of the DNA ladder:
Adenine
Adenine
Thymine
Thymine
Cytosine
Cytosine
Guanine
Guanine
Chargaff's Rule!
Chargaff's Rule!
Erwin Chargaff - Discovered that the amount of A was the same amount of T. A = T and G = C!
Erwin Chargaff
A matches T and C matches G
A matches T and C matches G
3 hydrogen bonds connect G with C.
2 hydrogen bonds connect A with T.
Which pair of bases do you think has a stronger bond? G and C or A and T?
The answer is G and C. This is because there are 3 hydrogen bonds between the bases.
Practice
If 20% of a DNA sample was Adenine, how much of the sample would be Thymine?
The answer is 20% because A matches with T.
If 10% of a DNA sample was Adenine, how much of the sample would be Cytosine? The answer is 40% because A + T = 20%. That leaves 80% for C + G. Half of 80% is 40%
Nucleotides
Nucleotides
Nucleotides are the smallest unit or subunit of DNA. Each nucleotide is a monomer. Monomers link up to form a polymer.
Each nucleotide contains a sugar molecule (deoxyribose), a phosphate group, and a nitrogen base (A, T, C, G).
Nucleotides join together to make huge DNA molecules. DNA is a polymer.
DNA is made of repeating units called nucleotides.
A and T form a base pair. G and C form a base pair.
The bases stick out from the sugar and pair with bases from the other strand to form the “rungs” of the ladder.
Each sugar connects to a base and two phosphates.
DNA Structure
DNA Structure
Information concerning how your body is built, as well as how it is supposed to function, is stored in the base sequence of DNA. In fact, the order of bases (A, T, G, and C) stores the information.
The backbone or sides of DNA are made of alternating sugars and phosphate groups.
The rungs of the ladder are made of base pairs: A + T and C + G.
Deoxyribose sugar connects to phosphate as well as a nitrogenous base.
All living things use DNA, but the sequence of bases is different in each organism.
DNA is a polymer – that means it is made from lots of small, almost identical, units called nucleotides.
“Poly” = many
“Mer” = parts
So "polymer" literally means “many parts.”
Mutations!
A change in the sequence of DNA is called a mutation.
Mutations can be neutral, beneficial, or harmful.
DNA Replication
DNA Replication
Chromosomes are bundled forms of DNA. Humans have 46 chromosomes.
To copy itself, DNA unwinds and the two strands separate. As this happens, new nucleotides match up with each of the original strands.
The end result is 2 new DNA copies, each with a newer side as well as the older, original side.
Humans have 46 chromosomes in their body cells, but we humans have 23 chromosomes in each gamete (sperm or egg cell). The chromosomes undergo segregation during meiosis to make this happen.
Think of DNA as a reference book that cannot leave the library. The nucleus is like the library.
You can make a copy of the DNA, however. This copy is called messenger RNA, or mRNA. The copy goes to the ribosome which is like a 3-D printer, or factory.
Building supplies in the cells are amino acids. They are sort of like bricks, cement, wood and nails.
Amino acids are put in order on the ribosome to make protein, the finished product that is used in the body. More information concerning protein synthesis can be found here.
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