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