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Inside the Nucleus Interest Grabber

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

DNA Nucleotides Purines Pyrimidines Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose

Structure of DNA DNA Structure Link Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

Chargaff’s Rules

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

James Watson & Francis Crick

Chromosome Structure of Eukaryotes Nucleosome Chromosome DNA double helix Coils Supercoils Histones Chromatin

Chromosome Structure • 1 nanometer = 0.001 micrometer • 1 micrometer = 0.001 millimeter • So • 1 nm = 0.000001 mm

DNA Replication Original strand New strand DNA polymerase Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

Replication Link

Replication – Making New DNA • Helicase separates two strands of DNA by breaking hydrogen bonds • Primase starts replication • DNA polymerase “polymerizes” the individual nucleotides & proof-reads the new DNA

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

Messenger RNA Ribosomal RNA Transfer RNA Bringamino acids toribosome Combine with proteins tRNA mRNA Carry instructions rRNA DNA Ribosome Ribosomes RNA Concept Map RNA can be also called which functions to also called which functions to also called which functions to from to to make up

How is RNA different than DNA? • RNA • Contains ribose instead of deoxyribose • Single stranded • Nucleotide uracil replaces thymine

Transcription • Messenger RNA = mRNA • Carries amino acid sequence to the ribosome • Transfer RNA = tRNA • Carries 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

Codon

Transcription – Making a Copy of the DNA Transcription Link Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNApolymerase DNA RNA

Transcription – Making a Copy of the DNA • RNA polymerase separates the DNA strands at a promoter region on the DNA • mRNA adds nucleotides in sequence • RNA polymerase falls off the DNA at a terminator sequence on the DNA

RNA Editing • Introns - Intervening sequence = Junk DNA • Exons – Expressed sequence • Introns are cut out of the mRNA • Exons are held together by a cap and a poly A tail

The Genetic Code - Amino Acid Sequence 4 x 4 x 4 = 64Possible Codons for 20 amino acids AUG = Start Codon Begins transcription AAU, GAU, AGU Stop Codons which end transcription

Translation – On the Ribosome

Translation (continued) Translation Link

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.

Gene Mutations: Substitution, Insertion, & Deletion Deletion Insertion Substitution Frameshift Mutation

Chromosomal Mutations Deletion Duplication Inversion Translocation

Typical Gene Structure Promoter(RNA polymerase binding site) Regulatory sites DNA strand Start transcription Stop transcription

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

lac Operon

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. Gene Regulation

Cell Growth & Reproduction • Why replicate the DNA? • To make new cells • To replace old worn out cells • To replace damaged cells

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

Cell Size Limitations Surface Area-to-volume Ratio

Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume

Chromosome Structure • Sister chromatids • Centromere – attaches chromatids • 46 Chromosomes in humans

M phase (Mitosis) Interphase G1 phase S phase G2 phase Prophase Metaphase Anaphase Telophase Concept Map – Cell Cycle Cell Cycle includes is divided into is divided into

The Cell Cycle G1 phase M phase S phase G2 phase

Mitosis and Cytokinesis Spindle forming Centrioles Centromere Chromatin Centriole Nuclear envelope Chromosomes (paired chromatids) Interphase Prophase Spindle Figure 10–5 Mitosis and Cytokinesis Cytokinesis Centriole Metaphase Individual chromosomes Telophase Anaphase Nuclear envelope reforming

Mitosis and Cytokinesis Spindle forming Centrioles Centromere Chromatin Centriole Nuclear envelope Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Individual chromosomes Telophase Anaphase Nuclear envelope reforming

Interphase • Events of Interphase • Cell grows • DNA replicates • Centriole replication • NOT PART OF MITOSIS

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