Chapter 12 How Genes Work

Cooperative Activity 1. What do you know about DNA? 2. What do you want to know about DNA?

DNA & Today 1988: DNA profiling was used in Britain, murder of 2 girls 1994: OJ Simpson murder trial Crime shows Cold Cases

Review: What is DNA? DNA stores our genetic information Where is DNA found? Nucleus of cell

What is a gene? Section of DNA that codes for a trait Where are genes found? Chromosomes

What is a chromosome? Bundles of DNA Where are chromosomes found? Nucleus of cell

What do these words have in common? DNA Chromosomes Genes

Introduction Humans are made up of: 20,000 – 30,000 genes 23 pairs of chromosomes 3 billion nitrogen bases

Human Genome Genetic map of the human body Includes chromosomes and genes

Human Genome (cont.) You inherit 2 copies of every gene one from mom & one from dad

Human Genome (cont.) Only 1% of your DNA codes for genes

Human Genome (cont.)

Why are genes important? Genes contain the instructions to make proteins

Structure of DNA Made up of parts: nucleotides Chemical building blocks

Parts of a Nucleotide Nitrogen-containing Base (A, T, C, G) Sugar (Deoxyribose) Phosphate Group

Base Pairing Adenine (A) & Thymine (T) Cytosine (C) & Guanine (G) Hydrogen bonds hold bases together

Base Pairing

DNA – Basic Structure Backbone: Alternating Sugar & Phosphate Inside: Nitrogen Bases Shape: Double Helix

Structure of DNA

Making Copies of DNA Every time our body makes new cells, we need more DNA This process is called: DNA Replication

DNA Replication – Step 1 Helicase (enzyme) unwinds chains separates nucleotides by breaking bonds

DNA Replication – Step 2 2. DNA polymerase assembles new chains Complementary to one another

DNA Replication – Step 3 3. DNA ligase links the two sections

DNA Replication – End Result Two identical strands of DNA (Two daughter DNA)

Reading the Genetic Code Genes have the instructions to make proteins Occurs in two steps Transcription Translation

Review: Protein Synthesis Q: Which organelle helps make proteins? Ans: Ribosomes

Transcription Process of copying genetic information from DNA to mRNA (messenger) Takes place in nucleus

Carries copied info from nucleus to ribosomes Why do we need mRNA? Carries copied info from nucleus to ribosomes DNA cannot leave the nucleus Protect the code

1. Unwinds DNA double helix Transcription Steps RNA Polymerase 1. Unwinds DNA double helix 2. Adds RNA nucleotides to build mRNA chain

Transcription Steps (cont.) 3. mRNA moves out of nucleus

Transcription Animation

Translation Process of assembling amino acids into proteins on ribosomes Order of amino acid determines protein

Translation Steps tRNA (transfer) 1.) 3 letter code on tRNA anticodon matches up with mRNA codon tRNA (transfer)

Translation Steps (cont) 2.) tRNA interprets the mRNA code sequence 3.) Code is read 3 letters at a time

Translation Steps (cont) 4.) Amino acids bond together to form proteins

Mutations A change in the copying of the genetic message Can occur during DNA replication or transcription Rare - occur in 1 out of 1 billion bases

Factors that affect the rate of mutations Mutagens Radiation / UV light Chemicals

Translating The Code Example tRNA anticodon: AAA mRNA codon: UUU UUU codes for amino acid phenylalanine

Translation mRNA tRNA

Translation

Codon (mRNA) Table

RNA DNA Venn Diagram: RNA & DNA ribonucleic acid Structure A – U (Uracil) C – G Single stranded DNA deoxyribo- nucleic acid Structure A – T C – G Double stranded

MCAS Questions Which of the following statements best describes why the change in only one DNA base of the hemoglobin gene results in a different protein product of the gene? A. The change prevents mRNA from being made.  B. The change alters the amino acid sequence of the protein.  C. The change causes the blood cells to divide in an uncontrolled way.  D. The change creates a second strand of mRNA for each RNA molecule.

MCAS Questions In a eukaryotic cell, which of the following processes directly involves DNA? A. translation  B. cellular respiration  C. active transport of ions D. replication of chromosomes

MCAS Questions In a molecule of double-stranded DNA, the amount of adenine present is always equal to the amount of A. cytosine.  C. thymine. B. guanine.   D. uracil.

MCAS Questions During DNA replication, the wrong nucleotide was inserted in the DNA sequence. Which of the following terms describes this situation? A. mutation  C. transcription B. regeneration   D. translation

MCAS Questions A portion of one strand of a DNA molecule has the sequence shown below. ACCTGAAGG Assuming there are no mutations in this portion of the DNA, what is the corresponding sequence on the complementary DNA strand? A.ACCTGAAGG  C.TGGACTTCC  B.GTTCAGGAA  D.UGGACUUCC

MCAS Questions Fireflies produce light inside their bodies. The enzyme luciferase is involved in the reaction that produces the light. Scientists have isolated the luciferase gene. A scientist inserts the luciferase gene into the DNA of cells from another organism. If these cells produce light, the scientist knows that which of the following occurred? A. The luciferase gene mutated inside the cells.  B. The luciferase gene was transcribed and translated.  C. The luciferase gene destroyed the original genes of the cells.  D. The luciferase gene moved from the nucleus to the endoplasmic reticulum.

MCAS Questions Individuals with one form of lactose intolerance do not produce the enzyme lactase because the gene coding for the production of lactase is shut off in their cells. This means that which of the following processes does not occur for the gene? A. Hydrogenation C. replication B.mutation  D. transcription

MCAS Questions Which of the following statements best describes a DNA molecule? A. It is a double helix.  B. It contains the sugar ribose.  C. It is composed of amino acids.  D. It contains the nitrogenous base uracil.