briefly describe the steps of dna replication. agenda 1.replication math 2.transcription: making rna
TRANSCRIPT
Briefly describe the steps of DNA Replication.
Agenda1.Replication Math2.Transcription: Making RNA
DNA Info
• DNA never ever leaves the nucleus– DNA is the master copy of the directions a cell
needs to live so it needs to be protected
DNA in the nucleus is safe
But DNA in the cytoplasm can be destroyed
RNA
• RNA is a copy of DNA that goes out into the cytoplasm to tell the cell what to do in order to stay alive– RNA: ribonucleic acid
• RNA is similar to DNA– Sugar is ribose not deoxyribose– Nitrogen Base thymine is replaced with Uracil– Single stranded
RNADNA RNA
How many strands?
2 1
Nucleotide subunit
BasesThymine (T) Adenine (A)Guanine (G)Cytosine (C)
Uracil (U) Adenine (A)Guanine (G)Cytosine (C)
Phos-
phate Group
Deoxyribose Sugar
Nitro-gen
Base
Phos-
phate Group
Ribose Sugar
Nitro-gen
Base
T – A
G – C
U – A
G – C
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) – associates with proteins to form ribosomes
• Transfer RNA (tRNA) – transport amino acids to ribosome
Transcription
• RNA is made from 1 gene in DNA– Specifically mRNA (messenger RNA) because it
sends a message from DNA to the cytoplasm
DNA safe in the nucleus
Uses mRNA To send a message to the cytoplasm
Transcription
1. Unzip DNA 2. RNA Polymerase binds to synthesize RNA3. Match up bases to one side of a gene in DNA
in the 5’ to 3’ direction (adds to 3’ end)1. Use Uracil instead of thymine
4. mRNA detaches from the DNA5. mRNA moves out of the nucleus and into the
cytoplasm
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
Cytoplasm of cell
Nucleus
DNAmRNA
mRNA
Transcribe your DNA(get your paper from replicating DNA)
1. Does the mRNA model more closely resemble the DNA strand from which it was transcribed or the complementary strand that wasn’t used? Explain
2. Explain how the structure of DNA enables the molecule to be easily transcribed. Whys is this important for genetic information?
3. Whys is RNA important to the cell? How does an mRNA molecule carry information from DNA?
4. If DNA strand read AAC GTC GCG TAC, what would the mRNA strand be?
Briefly describe transcription.
Agenda1.Finish Transcribing DNA2.Translation
A little more about RNA
• RNA is shorter than DNA• DNA is interrupted by short sequences that are
not in the final mRNA– These are called introns
– Sequences that are kept in the final mRNA sequence are called exons
Translation
The Code
• 20 amino acids (AA) used to make proteins– DNA provides at least 20 different codes
• If each base coded for an AA then we could only get 4 AA
• If a pair of bases coded for an AA then we could get 16 (4x4)
• If 3 bases coded for an AA then we could get 64 (4x4x4)
The Code
• We find that every 3 bases codes for an amino acid sequence– Some amino acids are repeated
• Three base code is called a codon – All but 3 codons code for an amino acid
• A chart was made to show each AA that DNA/mRNA codes for
Translation
• mRNA is synthesized and moves to the ribosomes– Located on the Rough ER
• mRNA then attaches to the ribosome
• tRNA interprets the mRNA codon sequence and brings the appropriate amino acid– Several amino acids make proteins– Continues until a stop codon is reached (3)
tRNA
• 3 base sequence at the bottom – anticodon– Matches the codon on the mRNA strand
Ribosome
• 2 subunits – only together during translation– Attach the to mRNA strand– 3 grooves, E site, P site, and A site• Each groove holds a tRNA
– E site – exit– P site – add amino acid to polypeptide chain– A site – new tRNA arrives
Translate your DNA
Questions1.Write your Amino Acid Sequence2.Would you make a complete protein? Explain.3.Transcribe the following DNA sequence into
mRNA. Draw a line separating each codon:A T C G T C C A A A ….
Briefly describe translation
Agenda for Thursday Nov 4th
1.Review Replication, transcription, and translation
2.Practice
Replication
• DNA Helicase unzips DNA– Proteins bind to keep it apart
• Primers bind to DNA strands• DNA Polymerase adds nucleotides to DNA– Leading – continuous adding of bases– Lagging – Okazaki fragments
• DNA Ligase fills in gaps
Transcription
• DNA Helicase unzips DNA• RNA Polymerase adds bases to the template
strand of DNA– Only 1 strand of DNA gets copied
• RNA detaches from DNA strand• RNA moves into cytoplasm
Translation
• mRNA attaches to ribosomes• tRNA moves into ribosome• Anitcodon matches with mRNA strand and
adds and amino acid– tRNA leaves ribosome
• Stop codon is reached the amino acid chain (polypeptide) detaches from ribosome– Folds and creates a protein
DNA vs. RNADNA RNA
2 Strands 1 Strand
Deoxyribose sugar Ribose Sugar
A-TC-G
A-UC-G
How is RNA different from DNA
Agenda for Friday Nov. 5th 1.Quiz2.Practice with transcription and translation
Which RNA gets translated (mRNA, tRNA, rRNA)?
Agenda for Monday Nov 8th 1.Replication, transcription, translation (one last
time)1. Questions 2 and 3 on page 3352. Questions 1 – 4 on page 341
2.Practice3.Gene Regulation