Protein Synthesis 3.A.1.c. Genetic information flows from a sequence of nucleotides in a gene sequence of amino acids in a protein.

The “Central Dogma” of Molecular Biology

Protein Synthesis The process by which information stored in DNA (specific sequence of nucleotides) is used to produce proteins.

Remember how… RNA can boogie? mRNA:  carries information from DNA to the ribosome tRNA:  Molecules that bring specific amino acids to the ribosome, as dictated by the mRNA sequence. rRNA:  Structural components of ribosomes Regulatory RNA (RNAi): Control gene expression.

Transcription: DNA  RNA Where? -Within the nucleus (eukaryotes) -Starts at promoter -Ends at termination signal Who? -DNA -RNA polymerase -RNA What? - DNA is “rewritten” into mRNA

Transcription: DNA  mRNA How? RNA polymerase and transcription factors binds to promoter DNA unwinds 1 RNA polymerase reads DNA 3’  5’ adds complementary nucleotides to form an mRNA strand 2 RNA polymerase reaches termination signal mRNA and DNA are released 3

Transcription has just finished. What are we left with? mrna OR PRE-MRNA

Pre-mRNA Processing Addition of a poly-A tail to 3’ end Help mature mRNA out of nucleus Protect mRNA from degradation Help ribosomes attach to mRNA in cytoplasm Addition of a GTP (guanine triphosphate) or 5’ cap

Pre-mRNA Processing Splicing- removing introns snRNPs recognize sequences at the ends of introns Splicosomes remove introns and join exons

What is mRNA’s message? The message is sent in a code. The code is written in the sequence of nitrogenous bases.

The Genetic Code 3 Nucleotides = 1 Codon 1 Codon = 1 Amino Acid OR a Signal Amino Acids + Peptide bonds = Polypeptides Polypeptide(s) + Folding, Twisting, and more = Protein Signal Codons AUG – Signal to START translation, Amino Acid Methionine UAA UAG Signals to STOP translation UGA No Amino Acid Coding Do an example on the board. Write… AGU AUG CCU AUU GAG UAC CCC UAA GGA Indicate the codons How many codons will be transcribed? What AAs are coded for? Note: many amino acids have more than one codon.

Give it a whirl… AUGGACACACAUUAAUG AUG GAC ACA CAU UUA AUG Start Asp Thr His Stop

Translation: RNA  Protein Who? -mRNA & Codons -Ribosomes -tRNAs -Amino Acids What? - Amino acids are joined to form a polypeptide Where? -Within the cytoplasm -Starts at AUG (start codon) -Ends at a stop signal How? 1 Initiation 2 Elongation 3 Termination

This is tRNA. It carries 1 amino acid. It has an anticodon. They are related. How, you ask?

Anticodons Methionine Anticodon Codon Imagine an mRNA molecule… It has a codon: AUG What it the compliment to AUG? What amino acid does AUG code for? Imagine a tRNA carrying methionine… It has an anticodon: UAC What is the compliment to UAC? Anticodon Codon

It has 2 subunits It is made of rRNA and proteins This is a ribosome

Get it? This is translation. JK

Step 1 Initiation: Get it together Translation Step 1 Initiation: Get it together mRNA and rRNA (in the ribosome) interact, allowing the ribosomal subunit to bind to mRNA (initiation) tRNA (carrying methionine) binds to mRNA at AUG (start) codon Large ribosomal subunit comes to party too. Who? Ribosome, tRNA What? Bind to mRNA Where? AUG codon Why? They love each other : ) Anticodon? If AUG starts all translation… is the first AA in every polypeptide methionine? Pretty much, but it can be removed later.

Elongation: Build it up Translation Elongation: Build it up Second tRNA (with its own amino acid) attaches to the second codon First tRNA releases its methionine A peptide bond forms between the two amino acids First tRNA leaves the ribosome Ribosome moves down mRNA one codon What is the red amino acid? Cytosine What is the anticodon? ACA

Elongation: Build it up, more Translation New tRNAs keep moving in Each new amino acid attaches with peptide bonds Used tRNAs leave Ribosomes keep moving down until… What is the red amino acid? Cytosine What is the anticodon? ACA

Translation Ribosomes keep moving down until… What is the stop sign? UGA, UAA, UAG

NO amino acids are added at the stop codon Translation Termination: STOP Ribosome reaches STOP codon Polypeptide is released NO amino acids are added at the stop codon What is the red amino acid? Cytosine What is the anticodon? ACA

Disassembly: It all comes apart Translation Disassembly: It all comes apart All of the components come apart Ribosomes move away to translate again or find a new mRNA What is the red amino acid? Cytosine What is the anticodon? ACA

Many ribosomes can translate one mRNA molecule at once!

In prokaryotes, translation and transcription are coupled In prokaryotes, translation and transcription are coupled. They can happen at the same time! Why?

Fate of Polypeptides Polypeptides fold and coil due to amino acid sequence (R-group interactions) Post-translational modifications- addition of sugars, lipids, phosphate groups

Destinations

Fate of Polypeptides Polypeptides fold and coil due to amino acid sequence (R-group interactions) Post-translational modifications- addition of sugars, lipids, phosphate groups Signal peptides (sequences of amino acids) target polypeptides for different locations (EMS, mitochondria, chloroplasts, nucleus, etc)

Mutations Changes to the genetic information in a cell (genotype) can affect the phenotype of organisms by affecting protein structure and gene expression Source of all new genes Responsible for diversity of life

Mutations- Causes Mutagens- substances that cause mutations by interacting with DNA DNA Replication mistakes- 1/1,000,000,000 bases replicated in humans

Mutations Can be positive, negative, or neutral, depending on where they occur

Chromosomal Mutations Large scale mutations caused by changes to chromosome structure Mistakes made during cell division can cause chromosome number abnormalities

Mutations and Fitness Mutations only generate variation. Fitness is determined by the requirements of the environment.