Ch 10: How Proteins Are Made

Investigate! Death Cap Mushrooms Row 1 Who? Genus species name What? Why are these mushrooms called “death cap”? Row 2 Where? Where can this mushroom be found? In what areas of the US and world does it live? Why? Why is it poisonous? What does it do? Row 3 Identification? – What does this mushroom look like? Symptoms and treatment? Row 4 January 2007 poisonings Santa Cruz? What parts of the body are most impacted – why? GROUP SUMMARY

How Proteins Are Made

Protein synthesis

10.1: From genes to proteins Traits are determined by proteins that are both built according to instructions coded in DNA. Proteins have many functions: Act as enzymes Cell membrane channels etc Proteins are not made directly from DNA – are made from RNA

RNA: Ribonucleic Acid gets its name from the sugar group in the molecule's backbone - ribose. Is a nucleic acid - a molecule made of nucleotides linked together

DNA vs RNA DNA RNA Double stranded Sugar deoxyribose Bases A, T, C, G Single stranded Sugar ribose Bases A, U, C, G Has Uracil instead of Thymine U pairs with A

Ribose sugar contains one more Oxygen atom than deoxyribose sugar. RNA has U (Urasil) DNA has T (Thymine) RNA single strand DNA double strand

RNA Base Pairs

The RNA is then “deciphered” during translation to make a protein. The instructions for building a protein are found in a gene and are rewritten to a molecule of RNA during transcription The RNA is then “deciphered” during translation to make a protein. See Figure 1 . P. 208

Gene expression or protein synthesis – is the entire process by which proteins are made based on information encoded in the DNA. Transcription- Instructions for making a protein, “rewritten” from DNA to RNA Translation- cell uses 2 types of RNA to read instructions and put together amino acids to make a protein

Transfer of Information from DNA to RNA

Step 1: RNA polymerase binds to the gene’s promoter. Figure 2 p. 209 TRANSCRIPTION Step 1: RNA polymerase binds to the gene’s promoter. - promoter- a specific sequence that acts as a “start” signal for transcription.

-Follows base pairing rules Step 2: RNA polymerase unwinds and separates the two strands of the double helix, exposing the DNA nucleotides on each strand. Step 3: RNA polymerase adds complimentary RNA nucleotides as it “reads” the gene. -Follows base pairing rules A=U, C=G - eventually reaches a “stop” signal in the DNA. - in eukaryotes: is a sequence of bases - in prokaryotes: is the end of a set of genes

Transcription – Key points RNA is made from DNA. As the RNA polymerase adds nucleotides they are attached with covalent bonds. Behind the RNA polymerase, the two strands of DNA will close up by forming hydrogen bonds and reforming the double helix shape Many identical RNA molecules are made simultaneously from a single gene. In prokaryotes – occurs in cytoplasm In eukaryotes – occurs in nucleus

Transcription vs DNA replication RNA polymerase RNA nucleotides linked An RNA molecule is formed Only one part of strand is used as a template DNA Replication DNA polymerase DNA nucleotides are linked A DNA molecule is made Both DNA strands serve as templates

3 types of RNA tRNA (transfer RNA) mRNA (messenger RNA) 3 types of RNA are made during transcription, depending on the gene being expressed. tRNA (transfer RNA) mRNA (messenger RNA) rRNA (ribosomal RNA)

Messenger RNA (mRNA) form of RNA that carries the instructions for making a protein from a gene and delivers it to the site of translation. RNA instructions are written as a series of 3-nucleotide sequences on the mRNA called codons.

Each codon along the mRNA strand corresponds to an amino acid or can signal a start or stop Genetic Code See Figure 4 p. 211 The genetic code (codons) used by most organisms to translate mRNA is nearly universal.

EX: UCUGUA UCU = Serine GUA Valine

Decoding DNA - Turn to page 211 The DNA code is TACAACGTA The MRNA code will be TACAACGTA (DNA CODE) AUGUUGCAU The amino acid sequence will be AUG UUG CAU break into 3 letter codons AUG = start UUG = Leucine CAU = Histidine

Translation: putting together amino acids to make proteins Translation takes place in the cytoplasm. tRNA and ribosomes help in the synthesis of proteins. tRNA (trasnfer RNA)– single strands of RNA that temporarily carry a a specific amino acid on one end. Anticodon: 3-nucleotide sequence on a tRNA that is complimentary to an mRNA codon rRNA (ribosomal RNA) –part of the structure of ribosomes

Translation Figure 5 p. 212 ( Do NOT have to memorize) Know main ideas only

Part 1

Part 2

Review

10.2: Gene Regulation & Structure Prokaryotic and eukaryotic cells are able to control which genes are expressed and which are not depending on the cell’s needs.

Prokaryotes: gene expression is regulated by operons. Gene expression is switched OFF when REPRESSOR proteins block RNA polymerase from transcribing a gene. Eukaryotes: an enhancer must be activated for a eukaryotic gene to be expressed. Transcription factors initiate transcription by binding to enhancers and to RNA polymerases.

Introns and Exons Many eukaryotic genes are interrupted by segments of DNA that do not code for proteins Introns: long segment of nucleotides that have No Coding Information Exons: portion of gene that is translated into proteins After transcription, the introns are cut out, and the exons are joined. The exons are then translated.

Working copy of gene Enzymes cut out introns & keep exons Molecule used to make protein

Mutations Changes in DNA. Gene alterations are a mutation that changes a gene. Mutations can involve a change in a single molecule or an entire gene. Remember mutations from Ch 6? Rearrangement (translocation) Alteration (deletion, insertion, inversion, duplication)

Mini quiz The making of a RNA based on the sequence of nucleotides in DNA is called DNA replication Translation Transcription Gene regulation

The making of proteins from the information carried from the mRNA is called DNA replication Translation Transcription Gene regulation

A change in the genetic code is called Mutation Operon Codon Operator

Mutations that change one nucleotide in a gene are called Operon mutation Codon mutation Repressor protein Point mutation

Anticodons are found on the ______ molecule. mRNA DNA rRNA tRNA

Unlike DNA, RNA contains The sugar deoxyribose The nitrogen base uracil A phosphate group nucleotides

Transcription and Translation video 4 min