DNA: The Molecule of Heredity

If the DNA of one cell is stretched out, it makes a 7 ft. long string

There are about 5 trillion cells in the human body

If you connected all the DNA together, it would be long enough thatit would take light over 10 hours10 hours to travel its length

(ruptured bacteria)

• Codes for your genes

• Located inside the nucleus

in the form of chromosomes

• DNA is made up of repeating units called NUCLEOTIDESNUCLEOTIDES

• Nucleotides have 3 parts:– Simple sugar– Phosphate– Nitrogenous base

A) Simple sugar = deoxyribose (the sugar gives it its name deoxyribonucleic acid)

B) phosphate group

C) 1 nitrogenous base– Adenine– Guanine– Cytosine– Thymine A

B

C

Rules for Base Pairing: They are called complementary base pairscomplementary base pairs

B.     Adenine = Thymine

(A = T)

A.     Cytosine Guanine

(C G)

the lines between the letters are hydrogen bonds

C

G

A

A

T

G

Sugar

PhosphateNitrogen Bases

Review QUESTIONS??

How many parts are there in a nucleotide?

What is the simple sugar that makes up DNA?

What pairs with A?

What pairs with G?

QUESTIONS???

Find the complementary DNA strand that matches the following bases

ATGA = ____________

TTGC = ____________

Fun FactsIf you wrote down all of the bases in one cell, you would fill a stack of 1,000 phone books with A's, T's, G's and C's

Fun Facts

If you unraveled all your chromosomes from all of your cells and laid out the DNA end to end, the strands would stretch from the Earth to the Moon about 6,000 times.

Why do you think DNA is called a double helix?

DNA Replication

• The DNA in the chromosome is copied in a process called DNA DNA ReplicationReplication

Replication of DNA

• During Replication, each strand serves as a pattern or template, to make a new DNA molecule just like the original

Question???

What is DNA Replication?

Replication of DNA

DNA Replication

• All DNA strands are read from the 5’ to 3’ end

• The 5’ end terminates in a phosphate group

• The 3’ end terminates in a sugar molecule (deoxyribose)

DNA Replication

• Okazaki Fragments are short, newly synthesized DNA fragments that are formed on the lagging template strand (3’ to 5’ side) during DNA Replication

DNA Replication

• The leading strand is continuously built in the 5’ to 3’ direction

• DNA polymerase can only add new nucleotides to a free 3’ end of a growing chain or the Lagging strands. These are discontinuous with Okazaki fragments coming in to fill in the gaps

Biology Humor

Replication of DNA

• This process continues until the entire molecule has been unzipped and replicated.

• Each new strand formed is a complement of the original – part old, part new

Compare the 2 new strands formed through DNA Replication?

DNA Review• Basic structure is

made up of a nucleotide– Phosphate– Sugar

• Deoxyribose

– Nitrogen Base• A pairs with T• G pairs with C

• DNA Replication– Copying of DNA– DNA Helicase unzips the

DNA– Polymerase attaches the

free nitrogen base– Works the leading strand

(5’ to 3’) – Has to work backwards

on the lagging strand (3’ to 5’) & fill in the gaps with Okazaki fragments