Download dna 5

Central Dogma
Semiconservative
Replication = each strand
has 1 parent and 1 new
strand
Replication
• DNA Helicase unzips DNA
• RNA Primers bind to DNA strands
• DNA Polymerase adds nucleotides to DNA
– Leading – continuous adding of bases
– Lagging – Okazaki fragments
• DNA Ligase fills in gaps
DNA Replication
• Two strands open forming Replication Forks (Yshaped region)
• New strands grow at the forks
3’
5’
Parental DNA Molecule
Replication
Fork
3’
4
5’
Unwinding
1. DNA Helicase unwinds/unzips DNA strand
A. Hydrogen bonds are broken
Base Pairing
Steps
1. DNA Polymerase adds nucleotides
– only adds to the 3’ end of the DNA
– NEW strand is built in a 5’ to 3’ direction
A. Adds a 5’
Q: Will the strands be identical?
5’
3’
Parental DNA Molecule
3’
5’
Leading Strand
• Replicated as the DNA unwinds
• New nucleotides are added continuously
Lagging Strand
• Replicated away from replication fork
• Create fragments - Okazaki Fragment
– Fragments later connected
Joining
• DNA Ligase – links two sections of DNA together
Replication
• DNA Helicase unzips DNA
• RNA Primers bind to DNA strands
• DNA Polymerase adds nucleotides to DNA
– Leading – continuous adding of bases
– Lagging – Okazaki fragments
• DNA Ligase fills in gaps
Prokaryote vs. Eukaryote
Prokaryotes
• 1 origin
Eukaryote
• Many origins
DNA Info
DNA in the
nucleus is safe
But DNA in the
cytoplasm can
be destroyed
RNA – Ribonucleic Acid
• Copy of DNA that goes into cytoplasm
– guides synthesis of proteins
DNA
# of strands 2 Strands
RNA
1 Strand
Type of
Sugar
Nucleotide
Base pairs
Ribose
Sugar
A-U
C-G
Deoxyribose
sugar
A-T
C-G
3 types of RNA
• Messenger RNA (mRNA) – complementary to DNA
– C=G, A=U
– Travel from nucleus to ribosome
– Direct synthesis of protein
• Ribosomal RNA (rRNA) –forms ribosomes
• Transfer RNA (tRNA) – brings amino acids
Transcription
• RNA is made from 1 strand of DNA
– Specifically mRNA is made
DNA safe in
the nucleus
Uses mRNA
To send a
message to
the cytoplasm
Transcription
1. Unzip DNA (helicase)
2. RNA Polymerase binds to synthesize RNA
3. Match up bases to one strand of DNA
1. Uracil instead of thymine
4. mRNA gets modified
5. mRNA moves out of nucleus and into cytoplasm
DNA
mRNA
mRNA
Cytoplasm of
cell
Nucleus
Transcription
happens in the
nucleus. An RNA
copy of a gene is
made.
Then the mRNA that
has been made moves
out of the nucleus
into the cytoplasm
Once in the
cytoplasm, the mRNA
is used to make a
protein
A little more about RNA
• DNA is interrupted by short sequences that are
not in the final mRNA
– Called introns
– Exons = RNA kept in the final sequence
The Code
• Every 3 bases codes for amino acid sequence
– Three base code is called a codon
– All but 3 codons code for an amino acid
– AUG = start codon
Ribosomes
– 2 subunits – only together during translation
– Attaches to mRNA strand
tRNA
• Anticodon - 3 base sequence at the bottom
• Matches the codon on mRNA strand
Translation
• mRNA attaches to ribosomes
• tRNA moves into ribosome
• Anticodon matches with mRNA strand and
adds an amino acid
– tRNA leaves ribosome
• Stop codon is reached & amino acid chain
(polypeptide) detaches from ribosome
– Folds and creates a protein
Proteins
• Chains of amino acids
fold into a specific 3-D
shape to perform their
biological function
• Shape depends on
interactions among
amino acids
– Hydrogen bonding
What would be the complementary DNA
strand for the following DNA sequence?
Which direction (right to left or left to
right)
DNA 5’-CGTATG-3’
Translate mRNA
1. Write the Amino Acid Sequence for the following
mRNA
UUG CAG CGC AUG
1. Would you make a complete protein? Explain.
2. Transcribe and translate the following DNA
sequence. Draw a line separating each codon:
A T C G T C C A A
DNA vs. RNA
DNA
RNA
2 Strands
1 Strand
Deoxyribose sugar
Ribose Sugar
A-T
C-G
A-U
C-G
https://www.youtube.com/watch?v=TEQMeP9GG6M
Questions:
put on a separate sheet of paper.
1. Replicate this strand of DNA:
ATGCAGTCGATG
TACGTCAGCTAC
2. If a DNA strand were to replicate, would they be
the same or different? Why?
3. How does the structure of a DNA molecule help
account for the great variety of life that exists on
earth?
Transcribe DNA
1. If a DNA strand read AAC GTC GCG TAC, what would
the mRNA strand be?
2. Does the mRNA model more closely resemble the
DNA strand from which it was transcribed or the
complementary strand that wasn’t used? Explain
3. Explain how the structure of DNA enables the
molecule to be easily transcribed. Why is this
important for genetic information?
4. Why is RNA important to the cell? How does an
mRNA molecule carry information from DNA?
• https://www.youtube.com/watch?v=itsb2SqRR0