SUMMARY OVERVIEW OF PROTEIN SYNTHESIS TRANSLATION – PROCESS OF ASSEMBLYING POLYPEPTIDE FROM AMINO ACIDS DIRECTED BY mRNA Link to Cold Spring Overview

POLYRIBOSOMES – multiple ribosomes translate a single mRNA message in both prokaryotes and eukaryotes HW 4-8, #7) Campbell’s 17.4, Concept check #2: Describe how the formation of polyribosomes can benefit the cell. Animation Link Polyribosomes

Figure 17.22 Coupled transcription and translation in bacteria What is the advantage to bacteria to couple transcription and translation? ANS: Speed; Proteins can be made very quickly in response to changing environmental conditions

In eukaryotes transcription and translation are separated in space and time In Eukaryotes, separating transcription and translation allows for mRNA processing which potentially increases diversity of possible proteins that can be synthesized. In Prokaryotes transcription and translation are simultaneous;

3 Types of RNA are utilized in Translation: Messenger (mRNA), Transfer RNA (tRNA) and Ribosomal RNA (rRNA)

3 Types of RNA are utilized in Translation: Messenger (mRNA), Transfer RNA (tRNA) and Ribosomal RNA (rRNA) rRNA tRNA tRNA rRNA rRNA mRNA rRNA mRNA

Figure 17.13a The structure of transfer RNA (tRNA) IB – be able to sketch t-RNA molecule: Label Amino-acid attachement site, anti-codon, hydrogen bonds t-RNA is a single-stranded molecule. What force of attraction allows the RNA to fold back on itself? ANS: Hydrogen-bonding between complementary base pairs

LEVELS OF t-RNA STRUCTURE

Attachment of correct amino acid to tRNA is catalyzed by enzyme Aminoacyl tRNA synthetase Synthetase link

Figure 17.14 An aminoacyl-tRNA synthetase joins a specific amino acid to a tRNA

Figure 17.16 Structure of the large ribosomal subunit at the atomic level Nobel Prize in Chemistry 2009 for determining the structure of Ribosomes

Figure 17.15 The anatomy of a functioning ribosome E site (Exit Site) – ejects empty tRNA P site (Peptidyl t-RNA binding site – Contains t-RNA with growing polypeptide chain A site (Aminoacyl tRNA binding site) binds incoming amino to be added to polypeptide chain

Figure 17.17 The initiation of translation

Figure 17.18 The elongation cycle of translation Link to translation animation Link to sumanas translation

Figure 17.19 The termination of translation DNA Interactive animation

Figure 17.24 Categories and consequences of point mutations: Base-pair substitution

Figure 17.23 The molecular basis of sickle-cell disease: a point mutation

Figure 17.24 Categories and consequences of point mutations: Base-pair insertion or deletion

HW 4-8, #8) Campbell’s 17.5, Concept check #1: What happens when one nucleotide pair is lost from the middle of the coding sequence of a gene? ANS: Frame shift mutation – every triplet codon after deletion will potentially have changed amino acid or if a stop codon is prematurely read in new reading frame polypeptide chain could be shortened.

HW 4-8, #8) Campbell’s 17.5, Concept check #2: A gene whose template strand contains the sequence 3’TACTTGTCCGATATC5’ is mutated to 3’TACTTGTCCAATATC5’. For both normal and mutant genes, draw the double-stranded DNA, the resulting mRNA, and the amino acid sequence each encodes. What is the effect of the mutation on the amino acid sequence?

Figure 7.7 Overview of an animal cell Translation can occur in cytosol (water soluble proteins which will operate within cell) or at endoplasmic reticulum

Figure 7.11 Endoplasmic reticulum (ER) ENDOPLASMIC RETICULUM (ER) – MEMBRANE SYSTEM FOR DIRECTING SYNTHESIS OF PROTEINS TO BE SECRETED BY CELL OR EMBEDDED WITHIN MEMBRANES ENDOPLASMIC RETICULUM (ER) – Network of interconnected, flattened, membrane-enclosed sacs known as cisterane ROUGH (ER) – CONTAINS BOUND RIBOSOMES FOR PROTEIN SYNTHESIS SMOOTH (ER) – SITE OF LIPID AND CARBOHYDRATE BIOSYNTHESIS AND METABOLISM

Figure 17.21 The signal mechanism for targeting proteins to the ER SIGNAL HYPOTHESIS – DESCRIBES HOW PROTEINS THAT ARE TO BE SECRETED FROM THE CELL OR EMBEDDED IN MEMBRANE ARE TARGETED TO THE ENDOPLASMIC RETICULUM

Translocation Animation (1st 2 min excellent). SRP= Signal Recognition Particle: Binds Signal Sequence and pauses translation SRP Receptor (embedded in ER membrane) – docking site for Signal Recognition Particle and Ribosome Signal sequence – short sequence of polypeptides (typical length ≈ 20-30 amino acids) that marks protein to be translated in ER Link to narrated Signal Animation Good visual, no narration

HW 4-8, #9) Campbell’s 17.4, Concept check #3: Describe how a polypeptide to be secreted is transported to the endomembrane system. (Signal hypothesis)

Link to protein secretions NOT on OUR TEST; Is on IB/AP Exam

Post-translation Modification Additions, Deletions or Changes to originally translated amino acid

Example: Post-translational Modification: Insulin Insulin is synthesized as a single polypeptide chain that only becomes active after an enzyme cuts out central part of the chain

Post-translation Modification: Heme Group Heme groups contain an iron which is coordinate – covalent bonded to nitrogens a planar ring; Present in hemoglobin as site of oxygen transport and electron transfer proteins in electron transport chain.

Post-translation Modification: Phosphorylation Kinase enzymes catalyze the addition of phosphate groups (red-yellow) to a protein (green oval). Phosphorylation of proteins is often used in signaling pathways.

Signal transduction video Figure 11.17 Nuclear response to a signal: the activation of a specific gene by a growth factor Signal transduction video

Post Transcriptional Modification Histone acetylation