ANSWER KEY SI Worksheet #18 (Chapter 17)

ANSWER KEY SI Worksheet #18 (Chapter 17)

**** ANSWER KEY**** SI Worksheet #18 (Chapter 17)

BY 123

Meeting 11/12/2015

Chapter 17:

  1. What is transcription?

The synthesis of RNA under the direction of DNA.

  1. What type of RNA is produced during transcription?

mRNA

  1. What is translation?

The synthesis of a polypeptide which occurs under the direction of mRNA.

  1. Where are the sites of translation?

Ribosomes

  1. Discuss the differences in transcription and translation in eukaryotic organisms v. bacteria?

The basic mechanisms of transcription and translation are similar for bacteria and eukaryotes. Because bacteria do not have nuclei, their DNA is not segregated from ribosomes and the other protein-synthesizing equipment, this lack of segregation allows translation of mRNA to begin while its transcription is still in progress. In eukaryotic cells, the nuclear envelope separates transcription from translation in space and time.

  1. What is the central dogma?

DNARNAprotein

  1. What is the template strand?

For each gene, only one of the two DNA strands is transcribed. This strand is called the template strand because it provides the pattern for the sequence of nucleotides in a RNA transcript

  1. What is the relationship between the DNA template and the synthesized mRNA molecule?

A mRNA molecule is complementary rather than identical to its DNA template because RNA bases are assembled on the template according to base-pairing rules.

  1. What are codons? In which direction are they read by the translation machinery? And what does each codon specify?

The mRNA base triplets. 5’-3’. Each codon specifies which one of the 20 amino acids will be incorporated at the corresponding positon along a polypeptide.

  1. What is the start codon?

AUG, methionine (Met)

  1. What are the 3 stop codons?

UAA, UAG, UGA

  1. What is meant by there being redundancy but no ambiguity in the genetic code?

Few codons specify the same amino acid (redundancy), but neither of them ever specifies any other amino acid (no ambiguity)

For example: codons GAA and GAG specify glutamic acid (redundancy) but neither of them specifies any other amino acid

  1. What are the functions of each of the following molecules in transcription?
  1. RNA polymerase: an enzyme that links ribonucleotides into a growing RNA chain during transcription
  2. Promoter: a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place
  3. Terminator: in bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signal RNA polymerase to release the newly made RNA molecule and detach from the DNA
  1. What are the three stages of transcription?
  1. Initiation: after RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand
  2. Elongation: the polymerase moves downstream, unwinding the DNA and elongating the RNA transcript, the DNA strands re-form a double helix
  3. Termination: eventually the RNA transcript is released, and the polymerase detaches from the DNA
Top View