W HAT DOES DNA LOOK LIKE ? Unit 5: Seventh Grade.
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Transcript of W HAT DOES DNA LOOK LIKE ? Unit 5: Seventh Grade.
WHAT DOES DNA LOOK LIKE?Unit 5: Seventh Grade
FOR MANY YEARS, THE STRUCTURE OF A DNA MOLECULE WAS A PUZZLE TO SCIENTISTS
In the 1950’s, two scientists deduced the structure while experimenting with chemical models.
They later won the Nobel Prize for helping to solve this puzzle.
WHAT IS DNA? BREAKING IT DOWN
As you know, inherited characteristics are determined by genes.
Genes are passed from one generation to the next.
Genes are parts of chromosomes. Chromosomes are structures in the nucleus
of most cells. Chromosomes are made of protein and DNA
So, DNA is the material that makes up your chromosomes that determine your inherited characteristics
WHAT DOES DNA STAND FOR?
DNA stands for: Dexoyribo Nucleic Acid
But is written out as deoxyribonucleic acid
THE PIECES OF THE PUZZLE Scientists knew that the
material that makes up our genes must do two things:
Give instructions for building and maintaining cells
Must be able to be copied each time a cell divides so that each cell could contain identical genes
Scientists eventually discovered that DNA is made of subunits called nucleotides
NUCLEOTIDES: SUBUNITS OF DNA DNA is made of subunits
called nucleotides. A “subunit” is a
subdivision of a larger unit. For example: a subdivision
you live in is a smaller unit of a city or town.
It takes many subunits working together to make up a whole, functioning unit.
Nucleotides are the subunits that make up DNA
NUCLEOTIDES: THE SUBUNITS OF DNA
Although it may look complicated, the DNA in a cell is really just a pattern made up of different parts called nucleotides.
Nucleotides are molecules that, when joined together, make up DNA
NUCLEOTIDES: THE SUBUNITS OF DNA
Nucleotides are made up of a sugar, a phosphate, and a base.
All nucleotides are the same except for the base.
There are four different kinds of bases: Adenine Thymine Guanine Cytosine
THE FOUR NUCLEOTIDES
Each of the four bases has a different shape.
Scientists often refer to a nucleotide’s base by the first letter of it’s base A = Adenine T = Thymine G= Guanine C = Cytosine Annie Takes Good
Care
NUCLEOTIDES AND DNA
Imagine a set of blocks that has only four shapes, or an alphabet that has only four letters.
DNA is a long string of these blocks or letters.
CHARGAFF’S RULES
Edwin Chargaff, a biochemist, discovered that the amount of adenine (A) always equaled the amount of thymine (T). A = T
He also found out that the amount of guanine (G) equals the amount of cytosine (C) G= C Annie Takes Good Care
CHARGAFF’S RULES
These findings are known as Chargaff’s Rules
At the time, these findings were thought to be relatively unimportant, but later on, Chargaff’s rules helped scientists understand the structure of DNA
WATSON AND CRICK
After looking at x-ray images of DNA showing that DNA has a spiral shape, scientists James Watson and Francis Crick concluded that DNA must look like a long, twisted ladder.
This discovery eventually helped explain how DNA is copied and how it functions in a cell.
DNA’S DOUBLE STRUCTURE
DNA looks like a twisted ladder.
This shape is known as a double helix.
The sides of the ladder are made of alternating sugar and phosphate parts.
The rungs are made of a pair of bases.
RUNGS OF THE LADDER
The rungs of the ladder are made of the bases adenine, thymine, guanine, and cytosine.
Adenine on one side of the rung always pairs with thymine (A, T) Annie Takes
Guanine always pairs with cytosine on a rung (G,C) Good Care
MAKING COPIES OF DNA These pairings of the
bases allows the cell to replicate, or make copies of, DNA.
Each base only bonds with only one other base.
Furthermore, pairs of bases are complementary to each other. For example GCAC will
bond with CGTG Ex: TGCA will bond with:
HOW COPIES ARE MADE During replication, a DNA
molecule is split down the middle, where the bases meet.
As the bases are exposed, complementary nucleotides are added to each side of the split ladder.
Two new DNA molecules are formed. Half of each molecule is
the old DNA Half of each molecule is
the new DNA
WHEN COPIES ARE MADE
DNA is copied every time the cell divides
Each new cell gets a complete copy of all the DNA.