Chapter 17 Reading Guide: From Gene to Protein

What are mutagen? Give a few examples.

A mutagen is any agent that affects a change. Thus any carcinogen is a mutagen. Common Mutagens include: bromine, sodium azide, psoralen, benzene, x-rays, gamma rays, alpha particles, uv radiation

What does alternative RNA processing do for cells?

Allows same DNA transcript to produce multiple polypeptide chains.

Identify the roles of tRNA (transfer RNA) and Ribosomes of the translation process.

Brings amino acids to the ribosome, where proteins are constructed.

How does protein synthesis differ between prokaryotes and eukaryotes?

Eukaryotic mRNA molecules are monocistonic. Prokaryotic mRNA molecules are polycistronic.

What is the genetic code and why is it said to be universal?

It is known as "universal", because it is used by all known organisms as a code for DNA, mRNA and tRNA. The universality of the genetic code encompasses animals, plants, fungi, archaea, bacteria, and viruses.

What happens to the transcript RNA before it leaves the nucleus?

It is processed - intron removed.

The Central Dogma

It provides the basic framework for how genetic information flows from a DNA sequence to a protein product inside cells. This process of genetic information flowing from DNA to RNA to protein is called gene expression.

How are completed proteins changed so they can be targeted for a specific site?

One way cytosolic proteins are targeted within cells is by forming large macromolecular assemblies. Many proteins exist as monomers, which freely diffuse through cytoplasm, or as polymers, which form large-scale structures that dynamically distribute to distinct locations in the cell.

What is a promoter?

The DNA sequence where RNA polymerase attaches is called the promoter.

What is the advantage of the 5' cap and poly A tail?

They promote the export of mRNA and protect it from degradation, also it helps with ribosome attachment.

What generally occurs during transcription and translation?

Transcription: RNA is produced from DNA. Translation: is the process in which cellular ribosomes create proteins. RNA produced by transcription from DNA is decoded by a ribosome to produce a polypeptide.

List the steps of translation. Initiation, Elongation, and Termination.

mRNA attaches to Ribosome, AA's added 1 by 1, Stop codon terminates process

Describe the mechanism for splicing RNA

snRNPs and spliceosomes bend DNA and cut out introns.

Give an example of what happens if reading frames are altered.

could end up with a terminated AA chain or a misfolded protein product.

How does the protein process differ in prokaryotes and eukaryotes?

In prokaryotes, ribosomes attach and protein synthesis begins before RNA is even completely transcribed because the DNA is in the cytosol along with the ribosomes. Eukaryotes produce RNA and modify it in the nucleus before exporting it to the cytoplasm where protein synthesis begins.

List the highlights of the three stages of transcription. Use all important vocabulary!

Initiation: RNA polymerase binds to DNA at a specific sequence of nucleotides called the promoter. The promoter contains an initiation site where transcription of the gene begins. Elongation: Only one of the unwound DNA strands acts as a template for the RNA synthesis. RNA polymerase can only add nucleotides to the 3' end of the strand so like DNA, RNA must by synthesized in the 5' to 3' direction. Termination: RNA polymerase continues to elongate until it reaches the terminator, a specific sequence of nucleotides that signals the end of transcription.

Explain two main types of point mutations?

Insertions and deletions. They result in what is known as a frameshift mutation. When a nucleotide base is either inserted or deleted it disrupts the amino acids coded for from the site of the mutation on to the end of the gene.

Distinguish between exons and introns.

Introns are noncoding sections of an RNA transcript, or the DNA encoding it, that are spliced out before the RNA molecule is translated into a protein. The sections of DNA that code for proteins are called exons.

Explain each of the following types of mutations: Missense, Nonsense, and Silence.

Nonsense: the amino acid that should have been coded for is changed to a stop code and the protein terminates at this point. This will likely lead to a useless protein. Missense: the change in nucleotide leads for a different amino acid. This may have little effect, or it may greatly change the resulting protein. Silent: this type of point mutation is the least harmful as there is no noticeable effect on the protein. As there is redundancy in the amino acid coding scheme from mRNA this change in nucleotide base ends up not changing the amino acid coding at all.

Describe the flow of genetic information. Discuss the two steps and the connection between DNA and proteins.

The flow of genetic information follows the central dogma of molecular biology: DNA is copied as messenger RNA which in turn is the template for protein synthesis.

Find the amino acid that matches each codon: mRNA UCA GCG AAA CGA and UAG

UCA: Serine GCG: Alanine AAA: Lysine CGA: Arginine UAG: Stop

List several features about the genetic code. Why is it called redundant but not ambiguous?

Universal, triplet code, 3 step codons (64 total) The genetic code is described as redundant, because a single amino acid may be coded for by more than one codon.