Go to Section: Interest Grabber Inside the Nucleus.

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Interest Grabber

Inside the Nucleus

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Genes are made of DNA

DNA is composed of individual units called nucleotides

Three of these units form a code (codon).

The order, or sequence, of the code determine the meaning of the message

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Purines Pyrimidines

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

 DNA Nucleotides

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Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

 Structure of DNA

DNA Structur

e Link

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Chargaff’s Rules

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X-ray diffraction

Rosalind Franklin X-rayed DNA from a calf thymus gland but had no idea what it was

James Watson saw this x-ray & interpreted DNA as a double helix

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James Watson & Francis Crick

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Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Chromatin

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Chromosome Structure1 nanometer = 0.001 micrometer1 micrometer = 0.001 millimeter

So

1 nm = 0.000001 mm

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DNA Replication

GrowthGrowth

Replication fork

DNA polymerase

New strand

Original strand

DNA polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

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Replication Link

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Replication – Making New DNA

1. Helicase separates two strands of DNA by breaking hydrogen bonds

2. Primase starts replication

3. DNA polymerase “polymerizes” the individual nucleotides & proof-reads the new DNA

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Now that new cells have been made, new proteins will be needed.

HOW ARE PROTEINS MADE?

We first need to look at something called RNA

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from to to make up

RNA Concept Map

also called which functions to also called also called which functions towhich functions to

can be

RNA

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions

rRNACombine

with proteins tRNABring

amino acids toribosome

DNA Ribosome Ribosomes

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How is RNA different than DNA?

RNA•Contains ribose instead of deoxyribose

•Single stranded

•Nucleotide uracil replaces thymine

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Transcription

Messenger RNA = mRNACarries amino acid sequence to the ribosome

Transfer RNA = tRNACarries amino acid to the codon on mRNA

Codon = 3 nucleotide bases on mRNA which “code” for an amino acid

Anticodon = 3 nucleotide bases on tRNA which match up with the codon

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Codon

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RNADNA

RNApolymeras

e

Transcription – Making a Copy of the DNA

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

Transcription Link

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Transcription – Making a Copy of the DNA

1. RNA polymerase separates the DNA strands at a promoter region on the DNA

2. mRNA adds nucleotides in sequence

3. RNA polymerase falls off the DNA at a terminator sequence on the DNA

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RNA Editing

Introns - Intervening sequence = Junk DNA

Exons – Expressed sequence

1. Introns are cut out of the mRNA

2. Exons are held together by a cap and a poly A tail

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The Genetic Code - Amino Acid Sequence

4 x 4 x 4 = 64 Possible Codons for 20 amino acids

AUG = Start Codon Begins transcription

AAU, GAU, AGU Stop Codons which end transcription

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Translation – On the Ribosome

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 Translation (continued)

Translation Link

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Determining the Sequence of a Gene

DNA contains the code of instructions for cells. Sometimes, an error occurs when the code is copied. Such errors are called mutations.

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Substitution

Insertion

Deletion

Gene Mutations: Substitution, Insertion, & Deletion

Frameshift Mutation

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Deletion

Duplication

Inversion

Translocation

Chromosomal Mutations

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Regulatory sites

Promoter(RNA polymerase binding site)

Start transcription

DNA strand

Stop transcription

Typical Gene Structure

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Gene Regulation

Operon – A group of genes that operate together

Lac Operon = operon expressed in E. coli to use the sugar lactose

Operator – region where repressor protein binds

Promoter – region that signals beginning of operon

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lac Operon

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lac Operon

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lac Operon

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lac Operon

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Gene Regulation

Tying it altogether - the lac Operon Gene

E. Coli bacteria can synthesize lactase, which is an enzyme that breaks down lactose. Lactase is only synthesized in the presence of lactose. If there is no lactose in the environment, the gene is repressed.

•E. Coli has three genes that code for lactase. •It also has an operator and a promotor. •Without lactose, the lac repressor binds to the operator site. •With lactose, the repressor is removed •Once repressor is removed, RNA polymerase binds to the promoter •RNA is transcribed, which is then translated, and becomes the lactase enzyme.

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Cell Growth & Reproduction

Why replicate the DNA?•To make new cells•To replace old worn out cells•To replace damaged cells

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Cell Size Limitations

Why are cells so small?• Cell size Limitations - Diffusion (The bigger the cell the slower the diffusion - DNA (Large cells need more DNA to make more proteins) - Surface area to volume ratio

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Cell Size Limitations Surface Area-to-volume Ratio

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Cell Size

Surface Area

(length x width x 6)Volume

(length x width x height)Ratio of Surface Area

to Volume

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Chromosome Structure

Sister chromatids

Centromere – attaches chromatids

46 Chromosomes in humans

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includes

is divided into is divided into

Concept Map – Cell Cycle

Cell Cycle

M phase (Mitosis)

Interphase

G1 phase S phase ProphaseG2 phase Metaphase TelophaseAnaphase

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M phase

G2 phase

S phase

G1 phase

The Cell Cycle

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Figure 10–5 Mitosis and Cytokinesis

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

 Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Mitosis and Cytokinesis

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Interphase

Events of Interphase

•Cell grows

•DNA replicates

•Centriole replication

•NOT PART OF MITOSIS

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Prophase

Events of Prophase

•Chromatin condenses into visible chromosomes

•Centrioles separate & spindle fibers form

•Nuclear membrane breaks down

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Metaphase

Events of Metaphase

•Chromosomes line up at the equator

•Spindle fiber attaches to the kineticore of the centromere of each chromosome

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Anaphase

Events of Anaphase

•Kineticore breaks andsister chromatids separate

•Microtubules contract pulling sister chromatids toward the centrioles

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Telophase

Events of Telophase

•Nuclear membrane reforms

•Chromosomes uncoil

•Cleavage furrow forms separating the nuclei

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Cytokinesis

Events of Cytokinesis

•Cytoplasm divided into the two cells

•Cell plate appears in plant cells

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Control of the Cell Cycle

Cells continue to grow in number until they contact other cells

What makes them stop growing?

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A sample of cytoplasm is removed from a cell in mitosis.

The sample is injected into a second cell in G2 of interphase.

As a result, the second cell enters mitosis.

Effect of Cyclins

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Uncontrolled Cell Growth = Cancer

Cancer

Cell division does not stop and a tumor forms

The tumor damages surrounding tissues