Download DNA and RNA

DNA and RNA
Bio 100
Tri-County Technical College
Pendleton, S. C.
Here a little..there a little
• Griffith’s Transforming Factor Experiment
• Hershey and Chase and bacteriophages
• Bacteriophage (phage) is a virus that infects
bacteria
• Watson and Crick and the world has never
been nor will it ever be the same again
• Rosalind Franklin provided the key for
Watson and Crick’s success
Genes and DNA
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Nucleus of a cell contains chromosomes
Chromosomes are made genes
Genes are made of DNA.
Each gene is a part of a chromosome that
codes for a protein or a portion of a protein.
• The Human Genome Project
A Chromosome
Gene 1
Protein 1
Gene 2
Protein 2
Gene 3
Gene 4
Gene 5
Protein 3
Protein 4
Protein 5
DNA composition
• Composed of nucleotides
• Nucleotide
– base, sugar, phosphate
• Sugar of DNA: deoxyribose
• Bases of DNA
– adenine, thymine, guanine, cytosine
• Sugar is bonded to the base and the
phosphate
How are nucleotides put
together?
• Sugars and phosphates are linked to each
other to make a strand of nucleotides with
the bases sticking out from the strand.
• DNA has two of these strands.
• The whole thing looks like a ladder.
– Sides are made of sugar-phosphates
– Rungs are made of bases bonded with hydrogen
bonds
DNA base-pairing
• Adenine pairs with thymine
• Guanine pairs with cytosine
Adenine
Guanine
Thymine
Thymine
Cytosine Adenine
Cytosine
Adenine
Guanine
Thymine
RNA
• Composed of nucleotides
• Sugar of RNA -- ribose
• Bases of RNA
– adenine, uracil, guanine, cytosins
• RNA is single stranded
• Sugars and phosphates are linked to each
other to make a strand of nucleotides with
the bases sticking out from the strand.
Kinds of RNA
• Messenger-RNA (m-RNA)
– produced in the nucleus from DNA
• Transfer-RNA (t-RNA)
– found in the cytoplasm attached to amino acids
• Ribosomal-RNA (r-RNA)
– one of the components of ribosomes
– ribosomes also contain protein
Physiology of DNA
• What does DNA do?
• DNA is replicated.
– an exact copy is made
– each daughter cell resulting from cell division
has an exact copy of all the genes
• DNA is involved in protein synthesis.
– contains the blueprint for all the proteins the
cell needs to produce
DNA Replication
• 1. An enzyme breaks the attachments between the
two strands of DNA.
• 2. The two strands unzip exposing the bases.
• 3. Complementary nucleotides pair up with the
bases.
• 4. DNA-polymerase synthesizes covalent bonds
between sugars and phosphates of adjacent
nucleotides.
Base-pairing
• adenine-containing nucleotide pairs with a
thymine-containing nucleotide
• guanine-containing nucleotide pairs with a
cytosine-containing nucleotide
• The result is an accurate duplicate of the
originial DNA strand.
• The process is called semi-conservative
DNA replication
Semiconservative??
• neither original strand is
discarded
• each original strans serves as
a template for a new strand
• half is new, half is original
DNA Replication - When
• During the life cycle of the cell.
• Just before cell division
• During a stage known as the
“synthesis” stage
• Chromosome number is preserved
Protein Synthesis
Gene (DNA)
Transcription (takes place in the nucleus)
messenger-RNA
Translation (takes place in the cytoplasm)
Protein
Transcription
• DNA contains the code for the position of
each amino acid in a protein.
• Three-letter code
• Transcription transfers this code from DNA
to messenger-RNA
• Transcription takes place because of basepairing relationships.
Base-paring -- transcription
• During transcription
– adenine on DNA pairs with uracil on RNA
– there is no thymine in RNA
– guanine pairs with cytosine
• Code is transferred to m-RNA
• A sequence of three bases on m-RNA that
corresponds to the DNA code is called a
“codon”
What happens next?
• m-RNA leaves the nucleus and
enters the cytoplasm where it
attaches to a ribosome.
• t-RNA brings amino acids to
the ribosome attached to the mRNA
More about t-RNA
• has two ends
• one end is attached to the amino acid
• the other end contains an anticodon which is
complementary to a specific codon on the
m-RNA
• when the t-RNA approaches the m-RNA the
anticodon matches with its complementary
codon
Codon-anticodon Matching
• Insures that the correct amino acid is placed
where it belongs in the sequence of amino
acids
• As the codon-anticodon matching continues
amino acids are placed beside each other in
the sequence dictated by the original code
on the DNA on the chromosome in the
nucleus.
Role of the ribosome
• The ribosome moves along the m-RNA
strand and wherever there are two
adjacent amino acids the ribosome
synthesizes a peptide bond between
them.
• The result is chain of amino acids that
eventually becomes a part of a large
protein.
Let’s do transcription -Write the m-RNA strand that will be produced from the
DNA strand below.
AAA AGT GGT TGG TTT CTA CCC CCC CAA
The Rules:
adenine on DNA pairs with uracil on m-RNA
thymine on DNA pairs with adenine on m-RNA
guanine on DNA pairs with cytosine on m-RNA
Let’s Do Translation
• 1. Write down the m-RNA you created
from the DNA in the previous slide.
• 2. Look up the amino acids which are
coded for by the codons on the m-RNA
stand.
• When asked to do this on a test, the codon
chart will be provided.
Review roles of RNA
• m-RNA
– brings the code from the nucleus in the form of
codons to the ribosomes in the cytoplasm
• t-Rna
– brings the amino acids to the ribosome where
proteins are being synthesized
– contains the anticodon which matches with the
codon
What Happens With Mutations?
• A mutation is a change in the content of the
genetic message.
– A change in the base sequence of one or more
genes.
• There are different kinds of mutations.
• Point mutation
– involves only one or two base pairs in the DNA
Mutation Illustration
AAA AGT GGT TGG TTT CTA CCC CCC CAA
The above is the DNA strand we were working with.
Let’s say a mutation occurred to alter this strand as
shown below.
AAA AGT GGT TGC TTT CTA CCC CCC CAA
Transcribe this into m-RNA and then translate the m-RNA into a
protein. What are the results?
Sickle-Cell Anemia
• A mutation occurred sometime in the past
which caused the gene for hemoglobin in
affected individuals to translate into
defective hemoglobin r/t normal
hemoglobin.
• The red cells are sickle shaped in these
individuals and do not carry hemoglobin
well.
Moving right on along
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Lytic viral replication cycle
Lysogenic viral replication cycle
Retroviruses, reverse transcriptase, and HIV
Just the tip of the iceberg…it really wasn’t
the ice above the water than sank the Titanic
• Emerging viruses (SARS is latest example)
• Most authorities agree that it is only going
to get WORSE