Chapter 17 Objectives: From Gene to Protein

Define "codon" and explain the relationship between the linear sequence of codons on mRNA and the linear sequence of amino acids in a polypeptide.

A codon is a reading of three consecutive nucleotides of an mRNA molecule as one. The linear sequence of codons in mRNA codes for an amino acid which then creates a polypeptide once a series of codons creates a lot of amino acids.

Compare and contrast DNA replication with transcription.

DNA replication makes new DNA strand from a DNA template and uses DNA polymerase. Replication occurs only once, before the cell undergoes mitosis. Transcription makes a new RNA strand from a DNA template and uses RNA polymerase. Transcription is a continually occurring process throughout the life of the cell.

Explain how RNA is modified after transcription in eukaryotic cells. a. Define introns, exons, and spliceosome. b. Does this RNA processing occur in prokaryotes?

During the mRNA process, RNA is modified by removing introns and joins exons from eukaryotic pre-mRNA and produces mature mRNA that will move into the cytoplasm from the nucleus. Introns are intervening sequeneces that are spliced out so exons can pull together. Exons re expressed sequences that code for a protein. Spliceosome removes introns from the transcribed pre-mRNA. RNA processing can occur in prokaryotes.

Why is an insertion or deletion more likely to be harmful than a substitution?

Insertion and deletion are more harmful than substitution because insertion or deletion of nucleotides may alter the reading frame, producing a frameshift mutation.

Explain what it means to say that the genetic code is redundant and unambiguous.

The genetic code is redundant and unambiguous because most amino acids are specified by more than one codon but no codon specifies more than one amino acid.

Explain the general process of transcription, including the three major steps of initiation, elongation, and termination.

The main process if transcription is to synthesize DNA strand into RNA. Initiation begins when RNA polymerase binds to the promoter and then RNA polymerase unwinds helix and begins transcription. Elongation occurs when new nucleotides are added. Termination is signaled by a specific sequence of nucleotides that stops the coding of RNA nucleotides.

Define "point mutations". Distinguish between base-pair substitutions and base-pair insertions.

Point mutations are chemical changes in just one base pair of a gene. With a base pair substitution, the wrong base pair is present but the overall number of base pairs is correct. With base-pair insertions, is the addition of nucleotide pairs in a gene.

Explain why polypeptides begin with methionine when they are synthesized.

Polypeptides begin with methionine when synthesized because AUG codes for methionine and is the starting signal of a codon. AUG synthesize machinery to begin translating mRNA at that location.

Describe the significance of polyribosomes (AKA polysomes).

Polyribosomes enable a cell to make many copies of a polypeptide very quickly.

Compare where transcription and translation occur in bacteria and in eukaryotes.

Transcription occurs in the nucleus of eukaryotes, while translation occurs in the cytoplasm of eukaryotes. Both transcription and translation are coupled in bacteria, translation begins while mRNA is being synthesized.

Describe the process of translation (including initiation, elongation, and termination).

Translation moves mRNA out of the nucleus. During initiation, ribosomal binding of the mRNA begins which is signaled by AUG start codon. During elongation tRNA with growing peptide chain sits in P site of ribosome and then binds with new aa binds to A site and termination is signaled by a stop codon and the polypeptide is releasd and the ribosome dissociates.

Explain what determines the primary structure of a protein and describe how a polypeptide must be modified before it becomes fully functional.

Primary structure = amino acid order dictated by mRNA Chaperone proteins enable folding Sugars, lipids, or phosphates may be added Pieces may be removed More than one chain may be bound together.

Explain how RNA differ from DNA.

RNA differs from DNA because they use the nucleotide uracil in place of thymine. RNA also goes through two processes call transcription and translation to make proteins in our genes. DNA makes genes and RNA makes proteins in our genes. RNA is singles stranded and uses ribose instead of deoxyribose.

Explain how RNA polymerase recognizes where transcription should begin. Describe the role of the promoter, the terminator, and the transcription unit in eukaryotic transcription.

RNA polymerase recognizes where transcription should begin because it moves 3' to 5' on DNA template strand. RNA polymerase binds to the promoter to begin intiation. The promoter is the starting point of RNA polymerase in a nucleotide sequence. It is also a binding site. The terminator is the stop signal and is signaled by a sequence of nucleotides. The transcription unit binds t the correct sequence of RNA nucleotides and begins to copy the information.

Clearly describe the structure of ribosome and how its structure allows it to perform its function.

Ribosomes facilitate specif coupling of tRNA anticodons with mRNA codons in protein synthesis. The ribosome is composed of two ribosomal subunits, large and small, and are made of proteins and ribosomal rRNA. A ribosome has three bindind sites for tRNA. The P site hold the tRNA that carries the growing polypeptide chain. The A site holds the tRNA that carries the next amino acid to be added to the chain. The E site is the exit site, where discharged tRNAs leave the ribosome.

Briefly explain how information flows from gene to protein (describe the central dogma).

The central dogma provides the basic framework for how genetic information flows from a DNA sequence to a protein product inside cells. Information flows from gene to protein by DNA replication, then RNA synthesis (transcription), and lastly protein synthesis (translation).

Explain how tRNA is joined to the appropriate amino acid. a. Identify the enzyme required to do this.

tRNA is joined to the appropriate amino acid by the enzyme aminoacyl-tRNA sythetase.

Explain the significance of the reading frame during translation.

Codons must be read in the correct reading frame (correct groupings) in order for the specified polypeptide to be produced.

1. Define "gene expression".

Gene expression is the process that takes the information in a sequence of nucleotides that make up DNA and translates the information to make the cell's proteins.

Give an example of each type of mutation and note the significance of such changes (what is the outcome in terms of the protein produced from a gene with that mutation).

Missense mutation (THQ ONE BOIG FLY HAD ONE RED EYE), which results in a protein in which one amino acid is substituted for another Nonsense mutation (THE ONE BIG), in which a stop codon replaces an amino acid codon, leading to premature termination of translation Frameshift mutation (THE ONE QBI GFL YHA DON ERE DEY), which causes a change in the reading frame, leading to introduction of unrelated amino acids into the protein, generally followed by a stop codon. Deletion (THE ONE BIG HAD ONE RED EYE), lose of nucleotide pairs in a gene. Insertion (THE ONE BIG WET FLY HAD ONE RED EYE), the addition of a nucleotide pair in a gene.

Distinguish between a missense and a nonsense mutation.

Missense mutations still code for an amino acid, but not necessarily the right amino acid. Nonsense mutations change the amino acid codon into a stop codon, nearly always leading into a nonfunctional protein.

Define the term 'mutation'. Give an example of a physical and a chemical agent of mutation.

Mutations are changes in the genetic material of a cell or virus. Chemical agent mutations are most chemical mutagens, carcinogenic. Physical mutations

Describe the structure and function of tRNA.

The structure of tRNA has a clover-leaf structure having four arms. CCA end is recognized by the synthetase and the anticodon loop has three anticodons to sit on the complementary codons of mRNA. Two of the three bases are required to be complementary, and this is the essence of wobble.

List the three types of RNA that are involved in the transcription/translation process.

Three types of RNA are mRNA, tRNA, and rRNA.

Distinguish between transcription and translation.

Transcription is the DNA directed synthesize of RNA. Translation is the process of reading the nucleotide sequence of mRNA and ordering the correct amino acids to generate a polypeptide (protein).