Download mRNA (Messenger RNA)

DNA & RNA 12.1 & 12.2
DNA & RNA
•
DNA
–
Griffith and Transformation
•
Frederick Griffith – 1928, How certain types of
bacteria produce a serious lung disease known
as pneumonia?
–
Experiment Figure 12-2 ( the cause of pneumonia was
not a chemical poison released by the disease –
causing bacteria)
Transformation
– Added heat killed disease causing bacteria
and harmless bacteria – dies of pneumonia
– Transformation – Process in which one strain
of bacteria is changed by a gene or genes
from another strain of bacteria ( The process
where by bacteria are changed by absorbing
DNA from an outside source)
– example – when mixed together some
factors were transferred
–
Video link
Avery and DNA
•
1944 repeated Griffin’s work. Made an
extract that destroyed proteins, lipids,
carbohydrates, and other molecules like
RNA. None of these treatments affected the
transformation. Then they repeated the
experiment using an enzyme to kill DNA,
transformation did not occur.
– * The factor in Griffith’s and Avery’s
experiments that seemed to transform one
bacterium into another was made of DNA.
From these discoveries, biologists inferred
that genes themselves were probably
made of DNA.
Hershey-Chase Experiment –
Studied viruses – 1952
•
How Bacteriophages invade cells
– Bacteriophages – viruses that infect bacteria
» Composed of DNA core and protein coat
» When bacteriophages enters bacterium,
the virus attaches to surface of the cell
and injects genetic information into it.
» *Hershey and Chase concluded that the
genetic material of the bacteriophage
was DNA, not protein
The Structure of DNA
• Genes do 3 important things
– Genes carry information from
one generation to the next
– Genes determine the heritable
characteristics of organisms
– Genes can be replicated, or
copied, easily
Nucleotides
•
– made
of 3 basic parts
– deoxyribose – 5 carbon sugar
– phosphate group
– nitrogenous base
» adenine
» guanine
» Cytosine
» thymine
DNA Nucleotides
• DNA is made up of a series of monomers
called nucleotides. Each nucleotide has
three parts: a deoxyribose molecule, a
phosphate group, and a nitrogenous base.
There are four different bases in DNA:
adenine, guanine, cytosine, and thymine
Chargaff’s Rule
A=T
G=C
Rosalind Franklin
•
•
X-ray
evidence
Helix – spiral
shaped
similar to that
of a spring
The double helix
– Cricket and Watson saw picture of x-ray
and within weeks figured out the
structure of DNA.
– Watson’s and Cricket’s model of DNA
was a double helix
– Double Helix - 2 strands were wound
around each other. (Twisted Ladder)
– Base pairing – principle that bonds in
DNA can form only between adenine –
thymine, and between guanine –
cytosine.
DNA Structure
• Backbone – deoxyribose and phosphate
group
• Ladder steps – nitrogenous base
(connected with Hydrogen bonds)
Section Assessment
•
•
•
List the conclusions Griffith, Avery,
Hershey, and Chase drew from their
experiment
Describe Watson and Cricket’s model of
the DNA model
What are the four kinds of bases found in
DNA?
Answers
– Griffith and Avery: genes were
probably made of DNA
– Hershey and Chase: genetic material
of bacteriophage was DNA, not protein
– DNA is a double helix, in which two
strands were wound around each other
– Adenine, thymine, guanine, cytosine
DNA Replication and
Chromosomes
DNA Replication
• DNA Replication – copying process by
which a cell duplicates its DNA
– *During DNA replication, the DNA molecule
separates into two strands then produces
two new complementary strands following
the rules of base pairing. Each strand of
the double helix of DNA serves as a
template against which the new strand is
made
How
replication
occurs
When the DNA
unzips
Example
DNA replication
• Video
http://www.phsuccessnet.com/iText/Brows
eITEXTServlet?eventType=openIEXT&IS
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DNA Polymerase
•
– enzyme
that proofreads new
DNA strands, helping to ensure
that each molecule is a nearly
perfect copy of the original DNA
12.3 RNA and Protein Synthesis
• RNA
– 5 carbon sugar
– Phosphate group
– Nitrogenous base
RNA & Protein Synthesis
• Differences between RNA and DNA
RNA
DNA
Sugar
Ribose
Deoxyribose
Strands
1 strand
2 (double
helix)
Nucleic Acids C, A, G,
Uracil
A, T, G, C
Types of RNA
•
*There are 3 main types of RNA:
–
–
–
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA).
• mRNA (Messenger RNA) – RNA
molecule that carries copies of
instructions for the assembly of Amino
Acids into proteins from DNA to the
rest of the cell
• rRNA (Ribosomal RNA) – type of RNA
that makes up the major part of
ribosomes
• tRNA (Transfer RNA)– type of RNA
molecule that transfers Amino Acids
to ribosomes during protein synthesis
Transcription
– process
in which part of the
nucleotide sequence of DNA is
copied into a complimentary
sequence in RNA.
Transcription
• RNA polymerase binds to DNA and separates
the DNA strands. Then uses one strand of DNA
as a template from which nucleotides are
assembled into a strand of mRNA.
Transcription
• Video
http://www.phsuccessnet.com/iText/Brows
eITEXTServlet?eventType=openIEXT&IS
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Question
• ? How does RNA polymerase “know”
where to start and stop making an RNA
copy of DNA?
Answer
• The enzyme only binds to
regions of DNA known as
• Promotors – region of DNA that
indicates to an enzyme where to
bind to make RNA.
• There are similar signals which
causes transcription to stop
RNA editing
• Introns – intervening sequence
of DNA – cut out of RNA
sequencing in the cell nucleus
• Exon – Expressed sequence of
DNA codes for a protein – goes
out of a nucleus and forms
protein
• RNA Editing
Many RNA
molecules have
sections, called
introns, edited out
of them before
they become
functional. The
remaining pieces,
called exons, are
spliced together.
Then, a cap and
tail are added to
form the final RNA
molecule.
Genetic Code
•
•
• Codon – consists of 3 nucleotides
that specifies a single Amino Acid
that is added to the polypeptide.
– Example. UCGCACGGU
UCG – CAC
–
GGU
Serine Histidine
Glycine
• Proteins are made by joining
amino acids into long chains
called polypeptides.
• 20 Amino Acids
– 4 different bases (4x4x4 = 64)
» 64 possible three base
codons
Translation
decoding of an mRNA message
into a polypeptide chain
(protein)
• Figure 12-18
• *During translation the cell uses
information from mRNA to produce
proteins
– mRNA transcribes (transcription) from
DNA to cytoplasm
– Translation begins when mRNA
reaches ribosome where proper amino
acids attaches.
– tRNA attaches to mRNA. tRNA has an
amino acid attached to it, the 3 bases
on tRNA are called anticodons.
– The amino acids form a chain called a
polypeptide continues to grow till it hits
a stop codon.
Translation
• mRNA leaves nucleus and goes into
cytoplasm
• mRNA pairs up with Ribosome (goes into
it)
• tRNA attaches to mRNA and Ribosome.
• tRNA has an amino acid attached to it, the
3 bases (A, U, C, G) on tRNA are called
anticodons.
Translation
• Anticodons pair up with codons
• The amino acids form a polypeptide and
continues to grow until it hits a stop codon.
• Once stopped the polypeptide breaks off
and you have a new protein (polypeptide)
Protein Synthesis
• Video
• http://www.phsuccessnet.com/iText/Brows
eITEXTServlet?eventType=openIEXT&IS
BNUrl=%2FiText%2Fproducts%2F0-13036843-1%2Findex.html&ISBN=0-13036843-1&ITEXTOID=0-13-0368431&DisplayTitle=Prentice+Hall+Biology++2002&TitleInFrame=Y
The roles of RNA and DNA
• ?How is RNA like a blueprint?
• copy of the original
QUICK LAB
• A certain gene has the following
sequence of nucleotides:
• DNA: GACAAGTCCACAATC
• mRNA: CUGUUCAGGUGUUAG
• Write this sequence on a sheet of
paper
• Write the sequence of the mRNA
molecule transcribed from this gene
LAB
• Refer to figure 12-17. Reading the mRNA
codons from left to right, write the amino
acid sequence of the polypeptide
translated from the mRNa.
• mRNA: CUG UUC AGG UGU UAG CC
• Amino acid: Leucine-PhenylalanineArginine-Cysteine-STOP
• Repeat step 3, reading the codons from
right to left.
Analyze and Conclude
• Why did steps 3 and 4 produce
different polypeptides?
• Do cells usually decode
nucleotides in one direction only,
or in either direction?
Answer
• mRNA is not the same in both
directions
• cells usually decode nucleotides
in only one direction
Genes and Proteins
• Proteins have everything to do
with the color, shape and size of
a leaf or bloodtype of a human
and even sex.
• Amino acids = proteins =
enzymes = used to regulate
chemical reactions
Mutations
–
– changes in DNA sequence that affect genetic
information
•
*Gene mutations result from changes in a single gene.
Chromosomal mutations involve changes in whole
chromosomes
–
–
Gene mutations – change 1 amino acid in a chain, changes
protein can become unusable
Mutations that affect one nucleotide are called point mutations
because they occur at a single point in the DNA sequence.
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Chromosomal mutation
Deletion – loss of all or part of a
chromosome
Duplication – a segment of
chromosome is repeated
Inversion – oriented in the reverse
Translocation – part of a chromosome
breaks off and attaches to another
nonhomologous chromosome
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SECTION ASSESMENT
•
•
•
•
List the three main types of RNA.
What happens during transcription?
What happens during translocation?
What is a gene mutation? A Chromosomal
mutation?
• Describe the three main differences between
RNA and DNA?
• Using the genetic code, identify the amino acids
that have the following messenger RNA strand
codes. UGGCAGUGC
Answers
– mRNa, tRNA, rRNA
– RNA polymerase binds to DNA, separates the strands, and
then uses one strand as a template to assemble RNA
– The cell uses information from messenger RNA to produce
proteins.
– Gene mutations result from changes in a single gene.
Chromosomal mutations involve changes in whole
chromosomes.
– Sugar
– Strands
– Base
ribose
single
uracil
– Tryptophan – glutamine - cysteine
deoxyribose
double
thymine