BELL RINGER
1. Name the process in which cells divide.
2. What must happen first before DNA replicates?
3. What are the base pairing rules?
4. The enzyme________ is used for proofing & __________.
5. Using the diagram below can we identify the backbone in this
structure?
6. Name the structure indicated by the arrow & bracket below
Biology I
DNA
• DNA contains genes, sequences of
nucleotide bases
• These Genes code for polypeptides
(proteins)
• Proteins are used to build cells and
do much of the work inside cells
DNA Begins the Process
•DNA is found inside the nucleus
•Proteins, however, are made in the
cytosol of cells by organelles called
ribosomes
•Ribosomes may be free in the
cytosol or attached to the surface of
rough ER
Starting with DNA
• DNA ‘s code must be copied and
taken to the cytosol
• In the cytosol, this code must be
read so amino acids can be
assembled to make polypeptides
(proteins)
• This process is called PROTEIN
SYNTHESIS
RNA~ Ribonucleic acid
RNA like DNA consists of nitrogen bases,
sugar-phosphate polymers, but there are also
some differences.
There are 4 main differences b/t RNA & DNA:
 The sugar in RNA is ribose, DNA has
deoxyribose
 RNA is single stranded, DNA is double
stranded
 RNA contains the base uracil, DNA has
thymine
 RNA is smaller in size compared to DNA
Comparison of Structures
DNA & RNA
Structure of RNA
Since the base Thymine is being
replaced by the base Uracil let’s answer
the following:
For the following DNA sequence add the
complementary RNA nucleotides:
TTAGGCTGGATGCTAAC
 The complementary RNA sequence
would be:
AAUCCGACCUACGAUUG
Question:
What would be the
complementary RNA strand
for the following DNA
sequence?
DNA 5’-GCGTATG-3’
Answer:
• DNA 5’-GCGTATG3’
• RNA 3’-CGCAUAC5’

Another difference between DNA & RNA is in the
function. DNA has only one function~ STORING GENETIC
INFORMATION in it’s bases. But there are 3 main types
of ribonucleic acid; each has a specific job to do
1.
2.
3.
Ribosomal RNA (rRNA) ~ exists outside the
nucleus in the cytoplasm of cells in structures
called ribosomes. Ribosomes are small,
granular structures where protein synthesis
takes place.
Messenger RNA (mRNA) ~ “records"
information from DNA in the cells nucleus and
carry it to the ribosomes. They serve as
messengers to the cell.
Transfer RNA (tRNA)~ the function of transfer
RNA is to deliver amino acids one by one to
protein chains growing at ribosomes.
Transfer RNA
Messenger RNA
Ribosomal RNA
• The following diagram is an example for gene
expression how the information in DNA is
translated into organism’s traits
• RNA molecules are copied by copying part of the
nucleotide sequence of DNA into a
complementary sequence in RNA
• This process by which DNA is copied to RNA is
called Transcription, it requires the enzyme RNA
polymerase & occurs in the nucleus of cells
 Step 1~ Transcription begins when RNA
polymerase binds to the “promoter” site (a
specific sequence of DNA that acts as a
“START” signal)
 Step 2~ DNA polymerase unwinds & separates
the two strands of DNA
 Step 3~ RNA polymerase adds & links
complementary RNA nucleotides
 Transcription continues until RNA polymerase
reaches the “STOP” signal on DNA
Diagrams of RNA Transcription
mRNA Transcript
•mRNA leaves the nucleus through
its pores and goes to the ribosomes
• Proteins are made by the joining of
amino acids into long polypeptide
chains, which contain any combination
of the 20 AA.
• The language of mRNA is called the
genetic code.
• A sequence of 3 nucleotides in mRNA
codes for each AA, are called codons.
• Codons consists of 3 bases that specify
an AA, therefore the genetic code is read
3 letters at a time.
Example of Using Genetic Code
Below is an example of an RNA
sequence:
CGGUAAGAGUCG
 It would be read 3 bases at a time:
CGG UAA GAG UCG
 Each codon is represented by a
different AA:
CGG
UAA
GAG
UCG
Arginine ~ Stop ~ Glutamine ~ Serine
Let’s practice below:
• Using the following DNA sequence:
ATCGTAACCGTTCTG
• Transcribe the DNA sequence into an mRNA
sequence:
UAGCAUUGGCAAGAC
• Now break the mRNA sequence down where it
can be read:
UAG CAU UGG CAA GAC
• Now identify the Amino Acids:
Stop Hist Tryp Glut Asp
Use the code
by reading from
the center to the
outside
 Example:
AUG codes for
Methionine
•
•
•
•
•
GGG?
UCA?
CAU?
GCA?
AAA?
Messenger RNA (mRNA)
start
codon
mRNA
A U G G G C U C C A U C G G C G C A U A A
codon 1
protein methionine
codon 2
codon 3
glycine
serine
codon 4
isoleucine
codon 5
codon 6
glycine
alanine
codon 7
stop
codon
Primary structure of a protein
aa1
aa2
aa3
peptide bonds
aa4
aa5
aa6
Transcription
•
•
•
•
•
•
•
•
Proteins are made by joining
amino acids into long chains
called polypeptides. The
production of these proteins
is called protein synthesis.
Each polypeptide contains
any of ____ Amino Acids
The language of mRNA
instructions is called the _____
Codons contain___
nucleotides that specify a
single AA
Some AA are represented by
more than one codon
EX: __ codons specify AA
Leucine, what are they?
One codon AUG can
represent Methionine or
“START” codon for protein
synthesis.
 Stop codons are like
periods at the end of
sentence!!
Name the codons for
the following AA:
• Tyrosine
• Alanine
• Glutamine
Name the AA for the
following codons:
• AAA
• CUG
• UAG
THE MAKING OF PROTEINS
•
•
•
•
•
TRANSLATION
The decoding of an mRNA message into a
polypeptide chain (protein) is called translation,
which takes place on ribosomes
Amino Acids are transported by ribosomes & tRNA
molecules, which have specific regions that bond to
AA
The loop attachment has a sequence of 3
nucleotides called anticodons.
The tRNA anticodon is complementary & pairs with
the mRNA codons.
During translation or protein synthesis the cells use
info from mRNA to produce the proteins
 EX: The tRNA anticodon UAC would bind with the mRNA
AUG
codon_______
• mRNA is transcribed from the DNA in the
nucleus
• Translation begins when mRNA attaches
to a ribosome at the start codon
• The pairing of codons & anticodons
causes AA to attach to the growing
polypeptide chain
• Each AA is added to the chain until it
reaches a stop codon  ending
translation
Another Example of
Translation
Protein synthesis
Protein Synthesis Pt. 2
Translation
MutatIons
What is a Mutation?
 A mutation is a permanent change in the DNA
sequence of a gene. Mutations in a gene's DNA
sequence can alter the amino acid sequence of the
protein encoded by the gene.
There are two main types of mutations:
Gene & Chromosomal
Gene mutations results from changes in a single gene
there are two types:
Point & Frameshift Mutations
 Point mutations~ these affect one nucleotide,
because they occur at a single point in the
DNA sequence & substitutes one nucleotide for
another.
.
Example
DNA:
TAC GCA TGG AAT
mRNA: AUG CGU ACC UUA
AA:
Met Arg Thr Leu
 Substitution
DNA:
TAC GTA TGG AAT
mRNA: AUG CAU ACC UUA
AA:
Met Hist Thr Leu
 Frame shift mutations~ these include
inserting a extra nucleotide or deleting a
nucleotide, which shifts the “reading frame”
of the genetic message
DNA:
mRNA:
AA:
DNA:
mRNA:
AA:
TAC GCA TGG AAT
AUG CGU ACC UUA
Met Arg Thr Leu
 Insertion
TAT CGC ATG GAA T
AUA GCG UAC CUU A
Ile
Ala Tyr Leu
Normal hemoglobin (eight out of the 146 amino acid units of normal
hemoglobin)
Val
His
Leu
Thr
Pro
Glu
Glu
Lys
Sickle-cell hemoglobin (the same section as above as found in Sickle-cell
hemoglobin)
Val
His
Good red
blood cells
Leu
Thr
Pro
Val
Glu
Lys
Sickle cell blood
cells
pictures from:
www.cc.nih.gov/
ccc/
ccnews/nov99/
The function of normal human red blood cells, which are disk-shaped, is to
transport oxygen from the lungs to the other organs of the body. Each
red blood cell contains millions of molecules of hemoglobin that carries the
oxygen.
A slight change in the order of the amino acids in the hemoglobin molecule
(valine substituted for glutamine), which has only 146 amino acids, causes
sickle-cell disease. Abnormal hemoglobin molecules stick together and
crystallize deforming the red blood cells. The deformed blood cells then
clog tiny blood vessels impeding the flow of blood. Sickle-cell anemia kills
about 100,000 people per year in the US
The molecular basis of sickle-cell
disease
 Environmental
factors including
radiation, chemicals, and viruses, can
cause chromosomes to break; if the
broken ends do not rejoin in the same
pattern, this causes a change in
chromosomal structure.
Types of Chromosomal Mutations
Inversion: a segment that has become separated
from the chromosome is reinserted at the same place
but in reverse; the position and sequence of genes
are altered.
 Translocation: a chromosomal segment is removed
from one chromosome and inserted on another
chromosome
 Deletion is a type of mutation in which an end of a
chromosome breaks off or when two simultaneous
breaks lead to the loss of a segment.
a. Even if only one member of pair of chromosomes is
affected, a deletion can cause abnormalities.
b. Cri du chat syndrome is deletion in which an
individual has a small head, is mentally retarded, has
facial abnormalities, and abnormal glottis and larynx
resulting in a cry resembling that of a cat.
 Duplication is a doubling of a chromosomal
segment.
a. A broken segment from one chromosome can simply
attach to its homologue.
b. Unequal crossing-over may occur.
Examples of Mutations
DELETION
DUPLICATION
INVERSION
TRANSLOCATION
Examples
Here’s the DNA Sequence
TACGCATGCTGCGAAACGTTGACT
Now transcribe into mRNA:
Now transfer mRNA into where it can be read:
Identify the AA
DNA: TAC GCA TGC TGC GAA ACG TTG ACT
mRNA: AUG CGU ACG ACG CUU UGC AAC UGA
AA:
Met- Arg- Thr- Thr- Leu- Cys -Aspar- Stop
Identify the Mutations Below
Original: THEBIGREDFOXATETHEBAT
How would it be read by mRNA? THE BIG RED FOX ATE THE BAT
What happened? THE BIG EDF OXA TET HEB AT
DNA: TAC GCA TGC TGC GAA ACG TGG ACT
mRNA: AUG CGU ACG ACG CUU UGC ACC UGA
AA:
Met- Arg- Thr- Thr- Leu- Cys -Thr- Stop
DNA: TAC GCA TGC TGC GAA ACG TGG AC
mRNA: AUG CGU ACG ACG CUU UGC AAC UG
AA:
Met- Arg- Thr- Thr- Leu- Thr -Aspar-