Eagle Zone-8 minutes (write the question and complete the sentence with an answer

from the word bank)

1. Mitosis makes __new nuclei.2. ______ coil and become condensed3. Along the middle of the cell, called the _____, sister

________start to align.4. When mitosis ends, _______ begins so cytoplasm can pinch

in half to make new cells called ________.5. Mitosis allows chromosomes to ________ and divide on their

own.

Word Bank:Reproduce chromosomes chromatidsCytokinesis two equator daughters

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2

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Why do we study DNADNA?

We study DNA for many reasons, e.g.,

• its central importance to all life on Earth,

• medical benefits such as cures for diseases,

• better food crops.

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Chromosomes and DNAChromosomes and DNA

• Our genes are on our chromosomes.

• Chromosomes are made up of a chemical called DNA.

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The Shape of the The Shape of the MoleculeMolecule

•DNA is a very long polymer.

•The basic shape is like a twisted ladder or zipper.

•This is called a double helix.

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The Double Helix The Double Helix MoleculeMolecule

•The DNA double helix has two strands twisted together.

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One Strand of DNAOne Strand of DNA• The backbone

of the molecule is alternating phosphates and deoxyribose sugar

• The teeth are nitrogenous bases.

phosphate

deoxyribose

bases

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NucleotidesNucleotides

C C

C

OPhosphate

O

CC

O -P OO

O

O -P OO

O

O -P OO

O One deoxyribose together with its phosphate and

base make a nucleotide.

Nitrogenous base

Deoxyribose

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One Strand of DNAOne Strand of DNA

• One strand of DNA is a polymer of nucleotides.

• One strand of DNA has many millions of nucleotides.

nucleotide

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Four nitrogenous basesFour nitrogenous bases

• Cytosine C• Thymine T

• Adenine A

• Guanine G

DNA has four different bases:

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Two Kinds of Bases in DNA

• PyrimidinesPyrimidines are single ring are single ring basesbases..

• PurinesPurines are are double ring double ring bases.bases.

C

C

C

C

N

N

OO

N

CC

CC

N

N

N

N

N

C

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Thymine and Cytosine Thymine and Cytosine are pyrimidinesare pyrimidines

• Thymine and cytosine each have one Thymine and cytosine each have one ring of carbon and nitrogen atoms.ring of carbon and nitrogen atoms.

C

C

C

C

N

N

OO

N

cytosinecytosine

C

C

C

C

N

N

OO

OO

thyminethymine

C

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Adenine and Guanine Adenine and Guanine are purinesare purines

• AdenineAdenine and and guanineguanine each have each have two rings of carbon and two rings of carbon and nitrogen atoms.nitrogen atoms.

C

C

C

C

N

N

N

AdenineAdenine N

N

C

C

C

C

C

N

NOO

N

GuanineGuanine N

N

C

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Two Stranded DNATwo Stranded DNA• Remember,

DNA has two strands that fit together something like a zipper.

• The teeth are the nitrogenous bases but why do they stick together?

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C

C

C

C

N

N

OO

N

C

C

C

C

N NOO

N

N

N C

Hydrogen BondsHydrogen Bonds• The bases attract each

other because of hydrogen bonds.

• Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.

• The bonds between cytosine and guanine are shown here with dotted lines

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Hydrogen Bonds, Hydrogen Bonds, cont.• When making

hydrogen bonds, cytosine always pairs up with guanine

• Adenine always pairs up with thymine

• Adenine is bonded to thymine here

C

C

CC

N

N

N

N

N

C

C

C

C

C

N

N

OO

OO

C

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Chargraff’s Rule:Chargraff’s Rule:

• Adenine and Thymine always join together

A T

• Cytosine and Guanine always join together

C G

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DNA by the NumbersDNA by the Numbers• Each cell has about 2

m of DNA.• The average human

has 75 trillion cells.• The average human

has enough DNA to go from the earth to the sun more than 400 times.

• DNA has a diameter of only 0.000000002 m.

The earth is 150 billion mor 93 million miles from the sun.

DNA Replication Video

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/micro04.swf::DNA%20Replication%20Fork

Eagle ZoneReplication Practice

• On your paper, complete the missing DNA strand by adding the complementary bases.

• A T C G T T G C C A T C• T A G C A A C G G T A G

Making Proteins

• The process of making proteins is called PROTEIN SYNTHESIS

• There are several steps to make a protein– Replication (DNA only)– Transcription (RNA)– Translation (RNA)

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Replication

• Copying of DNA• Makes a complementary strand• DNA CANNOT LEAVE THE NUCLEUS!• Write the complementary strand for the DNA

strand below using the base pairing rules learned earlier (Chargaff’s Rule)– GTA CCG ATC GGA

• Solution:– CAT GGC TAG CCT

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TYPES OF RNA

• RNA CAN leave the nucleus!• There are 3 main types of RNA

– Messenger RNA- (mRNA) carry copies of the DNA instructions OUT of the nucleus

– Transfer RNA- (tRNA) transfers each amino acid to the ribosome by coded messages from mRNA

– Ribosomal RNA- (rRNA) assembles proteins

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Transcription• RNA polymerase (an enzyme) binds to DNA

to separate the DNA strands• The nitrogenous base thymine (T) now

becomes uracil (U) in an RNA strand• Use the complementary DNA strand from

earlier (written below) to write the transcribed RNA strand (mRNA)- don’t forget the U’s!– CAT GGC TAG CCT

• Solution– GUA CCG AUC GGU

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Translation (protein synthesis) pg. 304-305 in

book• The cell uses information from messenger

RNA (mRNA) to produce proteins• What happens?

– mRNA comes out of nucleus into cytoplasm– tRNA carries amino acids to create anticodon

(complimentary bases to mRNA)– Ribosomes join with rRNA to break bonds to send

tRNA to work again

• Several amino acids in a chain make a protein

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