D N A

DEOXYRIBONUCLEIC ACID

DNA IS THE GENETIC MATERIAL

• Only understood hundreds of years after Mendel

• How do we know? Read about it before the test to answer the Level IV questions

DNA IS MADE OF NUCLEOTIDES

• 4 different bases, A, G, C and T

A STRAND OF DNA

• Sugar-phosphate backbone

DNA IS DOUBLE STRANDED

•Held together by Hydrogen bonds between bases• A T•G C

DNA FORMS A DOUBLE HELIX

• Suggested in 1953 by James Watson and Francis Crick• Don’t forget about Rosalin

d Franklin though

KEY DISCOVERIES OF DNA STRUCTURE

1. SEQUENCE OF NUCLEOTIDE BASES = CODE.

Stay tuned for C.O. 6.3 for more!

And there are 2 codes!

ATGCTAGGC +TACGATCCG

2. TWO COMPLEMENTARY STRANDS INCREASES ACCURACY

A G C T A C G C A T C

T C G A T G C G T A G

A G C T A C G C A T C

T C G A T A C G T A G

UV Radiation, Toxic Ooze, Etc.

A G C T A C G C A T C

T C G A T G C G T A G

A G C T A C G C A T C

T C G A T G C G T A G

A G C T A C G C A T C

T C G A T G C G T A G

Yay, I

didn’t get

cancer

3. EACH STRAND IS A TEMPLATE FOR BUILDING THE OTHER

DNA PACKAGING

• About 3,000,000,000 base pairs of DNA in every cell• Typing 60 wpm, 8 hours a day it would take you 50 years

to type out your genome

• Split into 23 pairs of chromosomes (46 total)

WHAT IS A CHROMOSOME?

• A very, very long sequence of DNA, coiled up very tightly• You have 23 pairs, one from mom, one from dad• Except if you are a guy instead of a pair of Xs you have

an X and Y

Why is this in an X? Stay tuned for C.O. 6.2!

UNDERSTANDING YOUR CHROMOSOMES

• Each chromosome contains thousands of genes, for a total of about 25,000• Genes actually make

up less than 1% of the DNA• What does the rest

do?• That’s what we’re

trying to find out! But it’s got something to do with gene expression!

DNA WRAPPING

• To understand how DNA is packaged, we will use pipe cleaners to represent segments of a chromosome• Each person begins with one pipe cleaner, which

represents about 8 million base pairs and 150 genes

DNA IS WRAPPED AROUND HISTONE PROTEINS

• We will use puffballs to represent histone proteins

WHY DOES THIS MATTER?

1. CONTROLS ACCESS TO THE DNA AND THUS THE EXPRESSION OF THE DNA

• E.g. epigenetics

Genes are accessible here

2. DNA MUST FIT IN A SMALL SPACE

• Amount of DNA in your body would go to the sun and back• 600 times!

• Each cell contains 5 feet of DNA packed into a nucleus with a radius of less than a hundredth of a millimeter

PACKAGE OUR DNA

• Wrap up your DNA in the histone proteins• Connect your DNA to the partners in your

group• Connect your group to the other groups in

the class• How small can we make our DNA!?

• ** not all that small because we used really large histone proteins to help you see what’s happening, but still!