Chapter 11 short answers (+ extra)

Finish this string of DNA with its complementary antiparallel strand. Use lines to indicate the number of bonds between nucleic acids.

AACGTATGCATCAGGA TTGCATACGTAGTCCT

What is the role of single-stranded binding protein in DNA replication?

Bind to single-stranded DNA to prevent hydrogen bonding between DNA strands, reforming double-stranded DNA

What is the central dogma of molecular biology and what three informational macromolecules are involved?

DNA→ RNA→ Protein; the central dogma states that DNA encodes messenger RNA, which in turn, encodes protein.

How does the process of translation differ between prokaryotes and eukaryotes?

In prokaryotes, transcription and translation may be coupled, with translation of an mRNA molecule beginning as soon as transcription allows enough mRNA exposure for the binding of a ribosome, prior to transcription termination. Transcription and translation are not coupled in eukaryotes because transcription occurs in the nucleus, whereas translation occurs in the cytoplasm or in association with the rough endoplasmic reticulum.

What are the three basic steps of transcription? Be able to describe what happens during each.

Initiation - the RNA polymerase unzips the DNA double helix Elongation - RNA Nucleotides are formed from the nucleotides in the DNA template strand Termination the mRNA that is formed leaves the nucleus

What are the three basic steps of translation (protein synthesis) and what occurs during each?

Initiation - transition complex forms, and the tRNA brings first amino acid in polypeptide chain to bind to start codon on mRNA Elongation - tRNA's bring amino acids one by one to add to the polypeptide chain Termination - release factor recognizes stop codon, translation complex dissociates, and completed polypeptide is released.

Describe the role of promoters and sigma factors in transcription.

It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase to gene promoters.

Why is primase required for DNA replication?

A primase is required for DNA replication because it synthesizes RNA primers needed to start replication

What is the role of a primer in DNA replication? Why is it important?

The primer is a short strand of DNA that serves as a starting point for DNA synthesis and it is important for DNA replication because the when DNA polymerases catalyzes the process, it can only add new nucleotides to an existing strand of DNA.

Why is it more likely insertions or deletions are more detrimental to a cell than point mutations?

frameshift mutations, caused by insertions or deletions of a number of nucleotides that are not a multiple of three are extremely problematic because a shift in the reading frame results Because ribosomes read the mRNA in triplet codons, frameshift mutations can change every amino acid after the point of the mutation.

There are 64 possible codons. How many amino acids are coded for with those codons and do all codons code for an amino acid?

61 of the 64 possible triplets code for amino acids, three of the 64 codons do not code for an amino acid; they terminate protein synthesis, releasing the polypeptide from the translation machinery.

Describe what happens when a nonsense mutation is introduced into the gene encoding transposase within a transposon.

A nonsense mutation will have thrown in a random stop codon in a gene.

What is the purpose of RNA processing in eukaryotes? Why don't prokaryotes require similar processing?

RNA processing in eukaryotes is required because it gets information into the cytoplasm in order for information to be translated into proteins, (mRNA may las serval hours). Prokaryotes do not have membrane bound nuclei, so mRNA lasts no more than 5 seconds.

What is meant by the genetic code being nearly universal?

The genetic code is nearly universal. With a few exceptions, virtually all species use the same genetic code for protein synthesis, which is powerful evidence that all extant life on earth shares a common origin.

Why does translation terminate when the ribosome reaches a stop codon? What happens?

Translation terminates when the ribosome reaches a stop codon because it does not code for a tRNA. Release factors cause the polypeptide to be released, and the ribosomal complex dissociates.

Explain the difference between a gene, a chromosome, a plasmid and a genome.

Gene = segments of DNA molecules that code for proteins or stable RNA molecules Chromosome = discrete DNA structure within a cell that controls cellular activities Plasmid = small, circular, double-stranded DNA molecule that is typically independent from the bacterial chromosome Genome = entire genetic content of a cell A genome contains the full complement of DNA within a cell and is organized into smaller, discrete units called genes that are arranged on chromosomes and plasmids.

When a new base is added to a strand of DNA, to which end is it added? (5' or 3')

When a new base is added, it gets added to the 5'- end (NOT ENTIRELY SURE IF THIS IS CORRECT)

Can two observably different cells have the same genotype? Explain.

Yes they can. Although multiple cells may have the same genotype, they may exhibit a wide range of phenotypes resulting from differences in patterns of gene expression in response to different environmental condition.

Briefly describe two ways in which chromosomal DNA from a donor cell may be transferred to a recipient cell during the process of conjugation.

1) Conjugation of the F plasmid : conjugation pilus bringing the two cells into contact. A single strand of the F plasmid is transferred to the F− cell, which is then made double stranded. 2) Conjugation of F' and HFr : The F plasmid can occasionally integrate into the bacterial chromosome, producing an Hfr cell. Imprecise excision of the F plasmid from the chromosome of an Hfr cell may lead to the production of an F' plasmid that carries chromosomal DNA adjacent to the integration site. This F' plasmid can be transferred to an F− cell by conjugation

Why is DNA replication considered semiconservative?

It is semi-conservative because in replication, each original strand is paired with a new strand, leaving each of the new DNA strands with one original and one new strand.

Draw and label the general structure of a mRNA paired to a tRNA with the appropriate amino acid attached.

SEE FIGURE

Explain why supercoiling is important and the role DNA gyrase plays.

Supercoiling is important because it extensively wraps the chromosomal DNA that is wrapped around histones, which makes the information in the DNA molecule inaccessible. DNA gyrase is used to relax the supercoiled DNA strands.

How does the ribosome know where to start translation? (two components to this) How does it know when to stop?

The ribosome knows to start translation once the untranslated region of the mRNA passes and it encounters the start codon (AUG). The ribosome continues translation until it reaches a stop codon. The translation of mRNA begins with the formation of a complex on the mRNA. Three initiation factor proteins bind to the subunit of the ribosome along with a Met (carrying the tRNA) bind to the mRNA near the start of the AUG start codon, forming the initiation complex. Initiation of translation occurs when the small ribosomal subunit binds with initiation factors and an initiator tRNA at the start codon of an mRNA, followed by the binding to the initiation complex of the large ribosomal subunit.