Genetics

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Part One Section One

DNA

The structure of DNA was figured out in 1953

James Watson and Francis Crick

These researchers (and Maurice Wilkins) received the Nobel Prize for their work, but their discovery wouldn’t have been possible without the work of Rosalind Franklin.

Rosalind Franklin

Franklin fired X rays at DNA crystals and took pictures of the patterns they made.

She discovered that the sugar-phosphate backbone of DNA was on the outside of the molecule, not the inside as was previously thought.

She discovered that DNA has two strands, not three as proposed in competing theories. She gave quantitative details about the shape and size of the double helix.

The missing piece of the puzzle, that she could not discover from her data, was how the bases paired on the inside of the helix.

In a few more months of study, she may have been able to figure this out as well.

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But Watson and Crick, who had been working on models of DNA for some time, learned of her research and put it all together. They were given the majority of the credit.

Some say Franklin should have also been awarded the Nobel Prize, but this became impossible when she died of cancer in 1958 at the young age of 37. Watson and Crick were awarded the Nobel Prize in 1962, (along with another x-ray crystallographer Maurice Wilkins) and the prize is never given posthumously.

Chromosomes to DNA

Deoxyribonucleic Acid (DNA)

Stores genetic information in a chemical “code”, a kind of blueprint of how to build a living organism

The “code” is used….. to build new cells to build proteins

DNAStructure: – “Double helix”• Like a spiral staircase

or a twisted ladder• Coiled up into

chromosomes

– Composed of nucleotides, which have three individual pieces:• Sugar (deoxyribose)• Phosphate• Nitrogen base

Phosphate

Sugar

Base

The 4 Nitrogen Bases

The nitrogen bases are held together by hydrogen bonds

A T

C G

2 Hydrogen

bonds

3 Hydrogen

bonds

Building New Cells:When a new cell is needed, the DNA will“unzip” and rebuild the missing pieces, resulting in two identical strands of DNA

The Cell Cycle

Cell Cycle

• Definition: The period of time from the beginning of one cell division to the beginning of the next.

• Happens in eukaryotic cells• What happens?

The cell replicates everything inside (all organelles) so that it is able to divide into 2 independent daughter cells.

Interphase• Gap 1: Cell grows and carries out normal

metabolism; organelles (cell parts) duplicate• Synthesis: DNA replicates and chromosomes

duplicate• Gap 2: Cell grows and prepares for mitosis

Mitosis: Stage of cell division

In total it takes about 16-24 hours to undergo the cell cycle depending on the type of cell that is dividing

INTERPHASE

After a cell has divided, the two new cells begin the process again,the cells at this stage are in Interphase.

Interphase is divided into three mini stages:- G1

S G2

Once the DNA has been copied, the cell can divide into two identical cells

Mitosis- the last stage of cell division