Chapter 12
MOLECULAR GENETICS
THE STRUCTURE OF DNA AND
DNA REPLICATION
DNA - DEOXYRIBONUCLEIC ACID
To understand genetics, scientists had to learn the
chemical makeup of the _______.
 Scientists discovered that genes are made of ____
 Scientists also found that DNA stores and
transmits the genetic information from one
____________ to of an organism to the next.
 Scientists began studying DNA structure to find
out how it carries info, decides traits, and
replicates itself.

DNA – THE STRUCTURE
DNA is a long molecule made up of units called
_________________.
 Each nucleotide contains a 5-carbon ________,
a __________ group, and a nitrogen-containing
_________.
 There are four kinds of bases in DNA:

 Adenine
(___)
 Guanine (___)
 Cytosine (___)
 Thymine (___)
THE NUCLEOTIDES
Green = 5-C sugar
Peach = phosphate
WATSON AND CRICK
Watson and Crick made a 3-D model of DNA.
 Their model was a ______________, in which
two strands are wound around each other.
 A double helix is like a twisted ___________

 ____________
and phosphates make up the side of
the ladder
 ________________ bonds between the bases hold
the strands together (the rungs)
DNA
CHARGAFF’S RULE
Aka the “base pairing rule”
 Chargaff’s rule states that bonds only form
between certain base pairs

___
always pairs with ___
___ always pairs with ___
You must memorize this!!!!
BASE-PAIRING
WHERE CAN YOU FIND DNA?
Most prokaryotes have one large DNA molecule
floating in the _____________.
 Eukaryotes have DNA in the _____________.
 Amazing fact:

 The
nucleus of a human cell contains more than 1
meter of DNA!
CHROMOSOMES
Contain both DNA and protein, which are tightly
packed together to form ____________.
 Chromatin consists of DNA that is tightly coiled
around proteins called ______________.
 This forms a beadlike structure called a
______________.
 Nucleosomes pack with one another to form a
thick fiber, which is shortened by a system of loops
and coils.
 Nucleosomes allow enormous amounts of DNA to
fit into such a small region.

DNA REPLICATION
Before a cell divides, it copies its DNA in a
process called ______________.
 During replication:

 The
DNA molecule ____________into 2 strands –
each strand of the DNA molecule serves as a model
for the new strand.
 Following the rules for _________________, new
bases are added to each strand.
 The end result is two ______________strands.
HOW DOES REPLICATION OCCUR?
It’s carried out by a series of enzymes
 Some enzymes “unzip” the molecule of DNA – the
hydrogen bonds between bases are broken
 The two strands unwind and serve as templates to
create two new strands
 The key enzyme is called DNA __________ – joins
individual nucleotides to produce a DNA molecule


DNA polymerase is also involved in “_____________”
each of the new DNA strands to minimize errors.
DNA REPLICATION
LET’S REPLICATE!
Original Strand = T A C G T T
New Strand = ______________
Original Strand = ATCGGCAATCACGAT
New Stand =
__________________
RNA AND
PROTEIN SYNTHESIS
RNA – THE BASICS
For a gene to work, the genetic instructions in
the DNA molecule must be ___________.
 The first step is to copy the DNA sequence into
___________.
 RNA is a molecule which contains instructions
for making ______________.

RNA – THE STRUCTURE

RNA is similar to DNA, except for:
 RNA
contains the sugar ______________
 DNA
 RNA
is _____________-stranded
 DNA
 RNA
has deoxyribose
is double stranded
has __________in place of thymine – A, U, C, G
 DNA
has A, T, C, G
RNA MOLECULES – WHAT DO THEY DO?

There are 3 kinds of RNA –
 Messenger
RNA (______)
 What
is this in the story? ______________
 Has the instructions for joining amino acids to protein
 Ribosomal
RNA (______)
 What
is this in the story? ______________
 Assembles the proteins
 Transfer
 What
RNA (______)
is this in the story? ______________
 Carries each amino acid to the ribosome according to the
coded message in mRNA
 Contains an anticodon to pair up with mRNA
TRANSCRIPTION
Process of making (or __________) RNA from DNA
 Occurs in the ____________
 During transcription:

DNA strands are separated
 RNA strand is built using one DNA strand as a template
 DNA is transcribed (written) into RNA following basepairing rules except that U binds to A

DNA Strand =
TACGCTACGCCTAATACT
New mRNA Strand = ____________________
TRANSCRIPTION TO TRANSLATION
The directions for making proteins are in the
order of the four nitrogenous _________
 This code is read _____ letters at a time

 Each
grouping of 3 letters is called a _________
 AUG/CGA/UGC/GGA/UUA/UGA
Each codon stands for one _______________
 There is one “start” codon and 3 “stop” codons

 Start
= AUG
 Stop = UGA, UAA, UAG
TRANSLATION
Process in which the cell uses info from mRNA to
make ___________
 Takes place in the _______________
 How does it work?

mRNA moves into the cytoplasm and attaches to
______________
 As each codon of the mRNA moves through the
ribosome, the proper amino acid is brought into the
ribosome by _________.
 The ribosome joins together each amino acid and the
protein chain grows.
 When the ribosome reaches a stop codon, the
polypeptide chain is ___________.

HOW DO WE FIGURE OUT THE AMINO ACIDS?

Use a Codon
Chart
LET’S DO AN EXAMPLE!
1.
2.
3.
4.
DNA Strand =
mRNA Strand =
TACGCTACGCCTAATACT
______________________
Split into codons =
______________________
Create Protein = ______________________________
______________________________
MUTATIONS
Mutations are ___________made when cells
copy their own DNA.
 Mutations are ___________in the genetic
material of a cell.
 There are two types of mutations:

 Gene
mutations – changes in a ___________gene
 Chromosomal mutations – change in the number of
structure of ___________________and affect
multiple genes
GENE MUTATIONS

__________mutations (substitution)–
 Occur
at a single point in the DNA sequence
 Causes one base to replace another, which only
affects one amino acid

___________mutations (insertion, deletion) –
A
base is added or removed
 All the codons are affected/changed resulting in a
completely different protein
CHROMOSOME MUTATIONS
Change in structure of chromosomes
 Four types:

 Deletions
= ABC-DEF  ___________
 Duplications = ABC-DEF  ____________
 Inversions = ABC-DEF  ___________
 Translocations = ABC-DEF  ___________
GH-IJKL
___________