Ch. 11: DNA Replication, Transcription, & Translation Mrs. Geist Biology, Fall Swansboro High School

Replication of DNA When the cell divides, a complete set of genetic instructions is generated for each new cell. When the cell divides, a complete set of genetic instructions is generated for each new cell. When an organism reproduces, genetic instructions pass from one generation to the next. When an organism reproduces, genetic instructions pass from one generation to the next. For this to occur, DNA must copy. For this to occur, DNA must copy. Template Mechanism Template Mechanism Negative and photograph” – The cell uses a negative of DNA to make more DNA. Negative and photograph” – The cell uses a negative of DNA to make more DNA.

Template Mechanism

DNA replication the 2 strands of the double helix separate using an enzyme. the 2 strands of the double helix separate using an enzyme. Each single strand serves as a “negative” for producing a new, complementary strand. Each single strand serves as a “negative” for producing a new, complementary strand. Nucleotides line up one at a time across from existing strand as predicted by the base-pairing rules. Nucleotides line up one at a time across from existing strand as predicted by the base-pairing rules. A pairs with T A pairs with T C pairs with G C pairs with G Enzymes link the nucleotides together to form two new DNA strands, called daughter strands. Enzymes link the nucleotides together to form two new DNA strands, called daughter strands.

From DNA to Protein “One Gene-One Polypeptide” Hypothesis- each gene encodes the instructions to produce one polypeptide “One Gene-One Polypeptide” Hypothesis- each gene encodes the instructions to produce one polypeptide Bases are like the language’s letters Bases are like the language’s letters Each gene is like a sentence Each gene is like a sentence

Ribonucleic acid (RNA) nucleic acid whose sugar is ribose nucleic acid whose sugar is ribose Contains uracil (U) instead of thymine (T) in DNA Contains uracil (U) instead of thymine (T) in DNA Single-stranded, sometimes twisted Single-stranded, sometimes twisted Several RNA molecules are involved in the steps from gene to protein Several RNA molecules are involved in the steps from gene to protein Messenger RNA (mRNA)- brings instructions from DNA in the nucleus to the ribosomes in the cytoplasm Messenger RNA (mRNA)- brings instructions from DNA in the nucleus to the ribosomes in the cytoplasm Ribosomal RNA (rRNA)- binds to mRNA and uses the instruction to assemble AAs in the correct order Ribosomal RNA (rRNA)- binds to mRNA and uses the instruction to assemble AAs in the correct order Transfer RNA (tRNA)- delivers AAs to the ribosome to make a protein Transfer RNA (tRNA)- delivers AAs to the ribosome to make a protein

From DNA to Protein DNA is converted to RNA during the process of transcription. DNA is converted to RNA during the process of transcription. Similar to a reporter transcribing a speech. The language remains the same, however the form of the message changes from spoken to written language. Similar to a reporter transcribing a speech. The language remains the same, however the form of the message changes from spoken to written language. RNA is converted to an amino acid sequence in a process called translation. RNA is converted to an amino acid sequence in a process called translation. Similar to translating English to Russian Similar to translating English to Russian Codon- a 3-base word in mRNA that codes for one amino acid Codon- a 3-base word in mRNA that codes for one amino acid Several codons translate into amino acids that make up a polypeptide Several codons translate into amino acids that make up a polypeptide

The Triplet Code Each codon stands for a particular amino acid Each codon stands for a particular amino acid 64 different codons 64 different codons Note: some amino acids are coded for by more than one codon. NO codon represents more than one amino acid. Note: some amino acids are coded for by more than one codon. NO codon represents more than one amino acid. Start codon: signals to start translating an RNA transcript Start codon: signals to start translating an RNA transcript AUG or methionine (Met) AUG or methionine (Met) Stop codon: DO NOT code for amino acids. Signal the end of each genetic message. Stop translating. Stop codon: DO NOT code for amino acids. Signal the end of each genetic message. Stop translating. UAA or UAG or UGA- stop UAA or UAG or UGA- stop

The Triplet Code

Transcription: DNA to RNA DNA template is transcribed into a messenger RNA (mRNA) in the nucleus DNA template is transcribed into a messenger RNA (mRNA) in the nucleus Only one of the DNA strands serves as a template for mRNA Only one of the DNA strands serves as a template for mRNA 2 DNA strands separate and then RNA bases pair with complementary DNA bases 2 DNA strands separate and then RNA bases pair with complementary DNA bases Remember: substitute U for T in RNA Remember: substitute U for T in RNA A transcription enzyme links the RNA nucleotides together A transcription enzyme links the RNA nucleotides together

Editing the RNA message In prokaryotes, the mRNA directly serves as the messenger that is transcribed into a protein In prokaryotes, the mRNA directly serves as the messenger that is transcribed into a protein In eukaryotes, the RNA transcribed is modified before it leaves the nucleus as mRNA to be translated In eukaryotes, the RNA transcribed is modified before it leaves the nucleus as mRNA to be translated Introns- internal noncoding regions Introns- internal noncoding regions Exons- coding regions of the RNA transcript Exons- coding regions of the RNA transcript Before RNA leaves the nucleus, enzymes remove introns and join exons together to produce the “final draft” Before RNA leaves the nucleus, enzymes remove introns and join exons together to produce the “final draft” Called RNA splicing Called RNA splicing

Translation: RNA to Protein Transfer RNA (tRNA)- transports and matches AAs to their appropriate codons on the mRNA transcript Transfer RNA (tRNA)- transports and matches AAs to their appropriate codons on the mRNA transcript Different version of tRNA molecule that matches each codon. Different version of tRNA molecule that matches each codon. At the one end of the folded tRNA molecule is a specific triplet of bases called an anticodon. At the one end of the folded tRNA molecule is a specific triplet of bases called an anticodon. At the other other end is a site where a particular AA can attach. At the other other end is a site where a particular AA can attach.

tRNA

Translation: RNA to Protein 1. A ribosome attaches to the mRNA strand. Molecules of tRNA, each carrying a specific AA, approach the ribosome. 2. The start codon, AUG, signals the start of proteins synthesis and codes for the AA methionine. The tRNA carrying methionine attaches to the ribosome and mRNA strand. 3. A new tRNA carrying an AA attaches to ribosome and mRNA strand next to the previous tRNA. AAs join by peptide bonds.

Translation: RNA to Protein 4. Ribosome slides along the mRNA to the next codon and the old tRNA molecule is released. A new tRNA molecule carrying an AA can attach to ribosome and mRNA strand. 5. Repeat steps 2-4 until a stop codon is reached on the mRNA strand.

Translation: RNA to Protein