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 showsCold 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?

DNAChromosomesGenes

IntroductionHumans 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

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.)

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 BasesShape: 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

2. DNA polymerase assembles new chains

Complementary to one another

DNA Replication – Step 2

3. DNA ligase links the two sections

DNA Replication – Step 3

Two identical strands of DNA (Two daughter DNA)

DNA Replication – End Result

Reading the Genetic Code Genes have the instructions

to make proteinsOccurs in two steps

TranscriptionTranslation

Review: Protein SynthesisQ: Which organelle helps

make proteins?Ans: Ribosomes

Transcription Process of copying

genetic information from DNA to mRNA (messenger) Takes place in nucleus

Why do we need mRNA?

Carries copied info from nucleus to ribosomes

DNA cannot leave the nucleus Protect the code

Transcription Steps

RNA Polymerase1. Unwinds DNA double

helix2. 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

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

MutationsA change in the copying of

the genetic messageCan occur during DNA

replication or transcriptionRare - occur in 1 out of 1

billion bases

Factors that affect the rate of mutationsMutagens

Radiation / UV light

Chemicals

Translating The Code

Example tRNA anticodon: AAA mRNA codon: UUU

UUU codes for amino acid phenylalanine

Translation

tRNA

mRNA

Translation

Codon (mRNA) Table

Venn Diagram: RNA & DNARNA ribonucleic

acid Structure

A – U (Uracil)C – G

Single stranded

DNA deoxyribo-

nucleic acid Structure

A – T C – G

Double stranded

MCAS QuestionsWhich of the following statements best describeswhy the change in only one DNA base of thehemoglobin 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 QuestionsIn a eukaryotic cell, which of the following processes directly involves DNA?A. translation B. cellular respiration C. active transport of ionsD. replication of chromosomes

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

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

MCAS QuestionsA portion of one strand of a DNA moleculehas the sequence shown below.

ACCTGAAGGAssuming there are no mutations in thisportion of the DNA, what is the correspondingsequence on the complementary DNAstrand? A.ACCTGAAGG  C.TGGACTTCC B.GTTCAGGAA  D.UGGACUUCC

MCAS QuestionsFireflies 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 QuestionsIndividuals with one form of lactoseintolerance do not produce the enzymelactase because the gene coding forthe production of lactase is shut off intheir cells. This means that which of thefollowing processes does not occur forthe gene?A. Hydrogenation C. replicationB.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.