Download Nucleic Acids

DNA & RNA
Chapter 12
What do you notice about these
pictures?
Nucleic Acids


Transmit & store genetic
information
Structure

Polymer = more than one unit


Monomer = one unit


Nucleic Acid
nucleotide
2 kinds of nucleic acid based on
the type of nucleotides
(monomers) used


DNA = deoxyribonucleic acid
RNA = ribonucleic acid
Nucleotide
DNA:
Deoxyribonucleic Acid
Nucleic acid that stores &
transmits genetic information
from one generation to the next
Why is DNA so important?


DNA is what we refer to as our Genetic
Code.
 You look like your parents because you
have their DNA in each of your cells.
 “carries” genetic information from
one generation to the next
 This DNA directs everything your body
does.
 If you need more enzymes in your
stomach to digest food, DNA has
the directions.
 Makes those four organic
molecules… can you remember
them??
Your chromosomes are very long DNA
molecules that are compacted and
condensed to fit inside the nucleus of a
cell.
Function:
1.
2.
Why is this organic molecule
important to living things?
Store genetic information.
Transmit genetic information.
Monomer:
Nucleic Acids
Polymer:
Nucleic Acid
Nucleotide
Example:
Nucleic acids carry that
genetic information during
reproduction to the new
offspring so that they possess
similar traits as their parents.
Adenine, Guanine,
Cytosine, Thymine.
Uracil
Example: DNA, RNA
The Structure of DNA

Chain (polymer) of nucleotides (monomer)



5-carbon sugar (pentose) = deoxyribose
Phosphate group
Nitrogen Base

4 kinds
The Nitrogen Bases
 Purines
2
rings
 Guanine
(G)
 Adenine
(A)
The Nitrogen Bases
 Pyrimidines
1
ring
 Cytosine
(C)
 Thymine
(T)
Notice how these parts can
look different…from last slide
Base Pairing

The nitrogen bases of two different
nucleotides pair up & connect via
Hydrogen bonds (Chargaff’s Rule)


Adenine & Thymine
Guanine & Cytosine
T
A
The Double Helix


“Twisting Ladder”
Nitrogen bases =
rungs of the ladder



Always a purine &
pyrimidine
1 ring + 2 rings = 3
rings across at all
points
Sugars & phosphates
= sides of the ladder
•
DNA Double Helix
DNA Replication
Tie in (s-phase of mitosis)

The ladder “unzips”


Complementary base pairing



Rungs of the ladder break = hydrogen bonds are
broken
The matching nucleotide (Chargaff’s Rule) is added to
each side of the ladder (sugar-phosphate backbone)
Started by enzyme DNA polymerase
Results in two new strands


Each is ½ old & ½ new
“Conserved” process
DNA Replication
Movie – 12 – DNA Replication
DNA Replication
DNA Polymerase
Why do we need DNA Replication?

Cell reproduction


Interphase – “S” synthesis phase
Provides that exact copy needed to pass
on the “same number & same kind” of
chromosomes
MCAS DNA Essay
Sample Answers
Organizing DNA

We already learned that chromosomes are the
condensed version of DNA





Why must DNA condense?
When must DNA condense?
Chromatin – unraveled, loose strands of DNA –
equals the helix
Histones – proteins used to wrap the loose
strands of chromatin around and start to spool it
into chromosomes
Nucleosome – unit of several histones with
chromatin wrapped around it
Eukaryotic Chromosome Structure
DNA & Traits




Traits are a specific characteristic
(ex. height)
Traits are controlled by genes
Genes are a certain piece of DNA
How does DNA give you a trait?



Makes a protein – the workhorse of the cell
The protein then controls (speeds up or slows
down) a reaction = enzymes
This reaction results in your trait =
phenotype
Proteins

Functions include




Carrying out chemical reactions (enzymes)
Pumping molecules in and out of cells
Helping cells move (flagella)
Structure

Polymer = more than one unit


Protein or polypeptide
Monomer = one unit

Amino acid
Building Proteins
Amino Acids are joined by a special
bond called a Peptide Bond.
Function:
1. Carry out chemical reactions
(enzymes)
2. Pump molecules in/out of cells
3. Help cells move (flagella)
Monomer:
Amino Acid
Example: Alanine, Serine
Why is this organic molecule
important to living things?
While nucleic acids carry
genetic information, proteins
execute that information.
Proteins
Polymer:
Protein, polypeptide
Example: amylase, flagella,
The Central Dogma
DNA
Messenger
RNA
Proteins
RNA – the other nucleic acid

RNA serves as the
intermediate for two
(2) processes
1. Needed to carry
the “message”
from DNA out of
the nucleus to the
ribosome

=Transcription
RNA – the other nucleic acid

RNA serves as the
intermediate for two
(2) processes
2. Needed to assist
in creating
proteins from this
message

=Translation
DNA vs. RNA
DNA
RNA
Structure
Double Helix
Single Strand
5-C Sugar
Deoxyribose
Ribose
Nitrogen
Bases
A, T, C, G
A, U, C, G
The new Nitrogen Base

Uracil



Replaces thymine
Pairs with adenine
Also a pyrimidine (single ring)
Transcription

The formation of a strand of RNA to carry
the “message” from DNA to the ribosome
in order to build proteins




Results in mRNA = messenger RNA
Contains a complimentary sequence to DNA
Uracil replaces any thymine bases by pairing
with adenine
Started by an RNA polymerase

Attaches to a specific spot where the gene starts promoter
Transcription
12 – Movie - Transcription
http://www.fed.cuhk.edu.hk/~jo
hnson/teaching/genetics/animati
ons/transcription.htm
mRNA
• made up of
codons
• codons are
groups of 3 bases
that will designate
an amino acid
(aa)
Codons
=3 bases on mRNA
 Each codon
corresponds to a certain amino acid



20 possible amino acids
Certain codons have special messages

Initiator codon – AUG (methionine)


Signals the start of protein synthesis
Stop codon – UAA, UGA, UAG

Signals protein synthesis to STOP
But there is more happening…

BEFORE the mRNA can leave the
nucleus…
•
Turns out there is EXTRA stuff in between
these codons that is junk
Intron – “intervening” pieces that do not code for
amino acids (aka JUNK)
 Exon – part that is “expressed” & codons are
translated into amino acids
 Now that it’s cleaned-up, it gets a cap & tail and
leaves the nucleus

mRNA
processing
Happens only in
Eukaryotes
(must have a
nucleus in
order to modify
it before it
leaves it!!)
mRNA
• mRNA leaves
the nucleus
• Travels to the
ribosomes
Sample Answers
12 – Movie - Translation
Translation



Protein synthesis directed by a strand of
mRNA
Uses the message from mRNA to
assemble a chain of amino acids =
protein
Uses two (2) new kinds of RNA
1.
rRNA = ribosomal RNA

2.
Makes up the actual ribosome (organelle section)
tRNA = transfer RNA

Transfers a roaming amino acid over to the
ribosome when it is needed
Transfer RNA (tRNA)


Carries an amino acid
to the ribosome
Has an Anticodon


3 bases on a tRNA
Matches up with codon
on an mRNA and
carries the amino acid
it corresponds to
http://www.fed.cuhk.edu.hk/~jo
hnson/teaching/genetics/animati
ons/translation.htm
The
ribosome binds new tRNA molecules and
amino acids as it moves along the mRNA.
Ribosome
mRNA
Start codon

The process continues until the ribosome
reaches a stop codon.
Translation


The sequence of
bases in DNA is
used as a
template for
mRNA.
The codons of
mRNA specify
the sequence of
amino acids in a
protein.
Translation
*amino acids joined by peptide bonds*
The Genetic Code


How are the instructions for assembling
amino acids into proteins encoded into
DNA?
There are 20 amino acids, but there are
only four nucleotide bases in DNA

So how many bases correspond to an amino
acid?

3 bases – 1 codon
The Genetic Code uses 4 letters written into
3-letter words
Cracking the Code


All 64 codons were deciphered by the mid1960s
The genetic code is redundant but not
ambiguous


no codon specifies more than one amino acid
Codons must be read in the correct
reading frame (correct groupings) in order
for the specified polypeptide to be
produced
The Genetic Code
The Genetic Code
*use the mRNA codon letters to find the aa*
How a gene is expressed
1.
2.
3.
4.
mRNA is
transcribed from
DNA
mRNA leaves
the nucleus
mRNA travels to
the ribosome
mRNA is
translated into
protein
# 1:Methionine-Threonine-Methionine-IsoleucineThreonine-Asparagine-Phenylalanine-Aspartic
Acid-Glutamine-Leucine-Proline
#2: Methionine-Proline-Arginine-Alanine-ProlineArginine-Cystiene-Arginine
#3: Methionine-Alanine-Proline-PhenylalanineValine-Arginine-Asparagine-Leucine-ValineGlutamic Acid-Lysine
#4: Methionine-Glycine-Histidine-PhenylalanineThreonine-Glutamic acid-Glutamic acid-Aspartic
Acid-Lysine-Alanine-Threonine-Isoleucine
When something
goes wrong during
DNA Replication….
DNA Mutations
Mutations: 12-4
Changes in the DNA sequence
that affect genetic information
How Mutations Happen

Mistakes in the sequence of DNA can happen
anytime

called DNA damage and can be caused by





UV light
Carcinogens
Viruses
DNA repair systems fix most these errors
If DNA repair does not fix the error before the
cell divides, it is now called a mutation

The new cell can not recognize that the code is
incorrect, that’s how it always was!
Mutations & Evolution

Germ Mutations



Occur in germ cells (sex cells)
Can be passed on to offspring
Somatic Mutations


Occur in somatic cells (non-sex cells)
Cannot be passed on to offspring
Types of Mutations

Chromosomal (chrsm)
 Affects
a large section of the DNA
 Compare to a book – affects whole pages
and chapters

Gene
 Affects
a single nucleotide, or several
nucleotides
 Compare to a book – affects letters and
words
Chromosomal Mutations
Deletion
 Duplication
 Inversion
 Translocation
 Non-Disjunction

 Trisomy
 Monosomy
 Polyploidy
Duplication & Deletion
Chromosomal Deletion
A large section (“chunk”) of the
chromosome is lost.
Chromosomal Duplication
A large section of the chromosome
is copied, and placed directly after
the original.
Inversion & Translocation
Chromosomal Inversion
A large section of the chromosome
is removed, and replaced in the
reverse order.
Chromosomal
Translocation
Large, uneven sections of chromosomes are switched
between two non-homologous chromosomes.
• Remember – crossing over is similar, but is even
amounts and between 2 homologous
chromosomes
Non-Disjunction


Non-Disjunction failure of homologous
chromosomes to
separate during
meiosis.
Results in gametes
with an abnormal
chromosome number
Disorders resulting from Nondisjunction

Polyploidy


An extra SET of
chrsms
Trisomy
One extra chrsm
 2N+1


Monosomy
Missing chrsm
 2N-1


Sex
Chromosomes

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
Turner’s
Syndrome = XO
Klinefelter’s
Syndrome = XXY
Jacob’s = XYY
Triple X = XXX
 Karyotype


Picture of a
person’s
chromosomes
Useful for
diagnosing
chromosome
mutations
Karyotypes
Gene Mutations

Point Mutations
 Change
in a single nucleotide (nt)
 “typos”
Substitution
 Inversion
 Insertion
 Deletion

Point Mutations
Substitution
• Replace a
single nt
• From TAGC
to TCGC
Example: Sickle-Cell Disease


Single nt
substitution results
in a change in one
Amino acid of the
protein that
confers the shape
of the red blood
cell.
Result: cell unable
to carry O2
Inversion
• Switching
the order of
two nt
• From TAGC
to TGAC
Insertion
• Insert an
extra nt
• From TAGC
to TCAGC
Deletion
• Loss of a
single nt
• From TAGC
to TGC
Homework
1. Copy the following information about Protein X:
Methionine—Phenylalanine—Tryptophan—Asparagine—
Isoleucine—STOP.
2. Use Figure 12–17 on page 303 in your textbook to determine
one possible sequence of RNA to code for this information.
Write this code below the description of Protein X. Below this,
write the DNA code that would produce this RNA sequence.
3. Now, cause a mutation in the gene sequence that you just
determined by deleting the fourth base in the DNA sequence.
Write this new sequence.
4. Write the new RNA sequence that would be produced. Below
that, write the amino acid sequence that would result from this
mutation in your gene. Call this Protein Y.
5. Did this single deletion cause much change in your protein?
Explain your answer.
Mutating your Name
Effect on Gene
Expression


Substitution or
Inversion can be
localized and affect
only a single amino
acid
Deletion or Insertion
results in frame-shift

Substitutions
usually affect
no more than
a single amino
acid.
Frame-shift Mutations

Mutation that shifts your “reading frame”
when translating the mRNA into amino
acids.




EX:
THE/FAT/CAT/ATE/THE/RAT
Delete the 1st H
Frameshifted: TE F/ATC/ATA/TET/HER/AT
Not only is the first amino acid affected, but
everyone thereafter

In an insertion,
an extra base is
inserted into a
base sequence.
MCAS DNA Essay
A sequence of DNA in a gene reads
GGT TCG AGA.
A.
B.
C.
D.
What is the sequence of amino acids that is
produced when this gene is translated?
If the DNA is mutated to read GGT TGG AGC,
what will the sequence of amino acids be?
Rewrite the original DNA sequence with a
single mutation that would not change the
sequence of amino acids.
Explain how a mutation can change the DNA
but not change the amino acid sequence.
Sample Answers
Homework: Which is
worse?

Chromosomal mutations or gene
mutations?




Write a short essay (5+ sentences) answering this
question.
Use the EFFECT of the mutation to defend your
example.
It may also be helpful to create an “example” trait
that is affected.
For the type you choose, which type of that
mutation is then the worse?