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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?.

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cooperative activity
Cooperative Activity

1. What do you know about DNA?

2. What do you want to know about DNA?

dna today
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
Review: What is DNA?
  • DNA stores our genetic information
  • Where is DNA found?
    • Nucleus of cell
what is a gene
What is a gene?
  • Section of DNA that codes for a trait
  • Where are genes found?
    • Chromosomes
what is a chromosome
What is a chromosome?
  • Bundles of DNA
  • Where are chromosomes found?
    • Nucleus of cell
  • Humans are made up of:
    • 20,000 – 30,000 genes
    • 23 pairs of chromosomes
    • 3 billion nitrogen bases
human genome
Human Genome
  • Genetic map of the human body
  • Includes chromosomes and genes
human genome cont
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
why are genes important
Why are genes important?
  • Genes contain the instructions to make proteins
structure of dna
Structure of DNA
  • Made up of parts: nucleotides
    • Chemical building blocks
parts of a nucleotide
Parts of a Nucleotide
  • Nitrogen-containing Base (A, T, C, G)
  • Sugar (Deoxyribose)
  • Phosphate


base pairing
Base Pairing
  • Adenine (A) & Thymine (T)
  • Cytosine (C) & Guanine (G)
    • Hydrogen bonds hold bases together
dna basic structure
DNA – Basic Structure
  • Backbone: Alternating Sugar & Phosphate
  • Inside: Nitrogen Bases
  • Shape: Double Helix
making copies 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
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
DNA Replication – End Result

Two identical strands of DNA (Two daughterDNA)

reading the genetic code
Reading the Genetic Code
  • Genes have the instructions to make proteins
  • Occurs in two steps
    • Transcription
    • Translation
review protein synthesis
Review: Protein Synthesis
  • Q: Which organelle helps make proteins?
  • Ans: Ribosomes
  • Process of copying genetic information from DNA to mRNA (messenger)
    • Takes place in nucleus
why do we need mrna
Why do we need mRNA?

Carries copied info from nucleus to ribosomes

DNA cannot leave the nucleus

Protect the code

transcription steps
Transcription Steps

RNA Polymerase

1. Unwinds DNA double helix

2. Adds RNA nucleotides to build mRNA chain

transcription steps cont
Transcription Steps (cont.)

3. mRNA moves out of nucleus

  • Process of assembling amino acids into proteins on ribosomes
  • Order of amino acid determines protein
translation steps
Translation Steps

1.) 3 letter code on tRNA anticodonmatches up with mRNA codon

  • tRNA (transfer)
translation steps cont
Translation Steps (cont)

2.)tRNA interprets the mRNA code sequence

3.)Code is read 3 letters at a time

translation steps cont1
Translation Steps (cont)

4.)Amino acids bond together to form proteins

  • 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
Factors that affect the rate of mutations
  • Mutagens
    • Radiation / UV light
    • Chemicals
translating the code
Translating The Code


    • tRNA anticodon: AAA
    • mRNA codon: UUU
  • UUU codes for amino acid phenylalanine



venn diagram rna dna

ribonucleic acid


A – U (Uracil)

C – G

Single stranded


deoxyribo- nucleic acid


A – T

C – G

Double stranded

Venn Diagram: RNA & DNA
mcas questions
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 questions1
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 questions2
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 questions3
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 questions4
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




mcas questions5
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 questions6
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 questions7
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.