Download Chapter 8 How Genes Work

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
Cytosine

(A) & Thymine (T)
(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
Why do we need mRNA?
Carries
copied info from
nucleus to ribosomes
DNA cannot leave the
nucleus
 Protect the code
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
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
Venn Diagram: RNA & DNA
RNA
DNA
 ribonucleic
 deoxyribonucleic acid
acid
 Structure
 Structure
 A – T
 A – U (Uracil)
 C – G
C – G
 Double
 Single
stranded
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.