Download Genetics Practice Questions C 1. Describe transcription

Genetics Practice Questions C
1. Describe transcription.
Transcription is the first part of the central dogma of molecular biology: DNA→RNA
It is the transfer of genetic instructions in DNA to mRNA. During transcription, a
strand of mRNA is made that is complementary to a strand of DNA.
2. How may mRNA be modified before it leaves the nucleus?
The mRNA may be modified in various ways such as splicing, editing, and polyadenylation.
• Splicing removes introns from mRNA.
• Editing changes some of the nucleotides in mRNA.
• Polyadenylation adds a “tail” to the mRNA. The tail consists of a string
of As (adenine bases).
3. What is the genetic code? What are codons?
The genetic code is the method by which the genetic information is encoded in a gene.
The genetic code consists of the sequence of nitrogen bases—A, C, G, T (or U)—in a
polynucleotide chain.
Codons are code “words” formed by the letters of four nitrogen bases in a
polynucleotide chain. The letters are combined in groups of three to show “words.”
4. Outline the steps of translation.
Translation is the process in which the genetic code in mRNA is read to make a protein.
When mRNA reaches a ribosome, the ribosome reads the sequence of codons in mRNA.
As the ribosome reads the codons, tRNA brings amino acids to the ribosome in the
correct sequence. As the amino acids are brought one by one to the ribosome, bonds
form between the amino acids, forming a polypeptide chain.
5. Use the genetic code from the chart in your notes to translate the following segment
of RNA into a sequence of five amino acids:
GUC-GCG-CAU-AGC-AAG
Valine-Alanine-Histidine-Serine-Lysine
6. The genetic code is universal, unambiguous, and redundant. Explain what this means
and why it is important.
・Universality・・・・All known living things have the same genetic code.
This is important because it shows that all organisms share a
common evolutionary history.
・Unambiguity・・・・Each codon codes for just one amino acid (or start or stop).
This is important because if one specific codon stood for more
than one amino acid, the proper sequence of amino acids by which
a protein is made could not be created.
・Redundance・・・・Most amino acids are encoded by more than one codon.
This is important because even if one of the four bases is in
short supply, the letters still have the possibility to make the
same amino acid they want to make.
7. How are transcription and translation related to the central dogma of molecular
biology?
Transcription is the DNA→RNA part of the central dogma of molecular biology. It
occurs in the nucleus. During transcription, a copy of mRNA is made that is
complementary to a strand of DNA.
Translation is the RNA→protein part of the central dogma of molecular biology. It
occurs at a ribosome. During translation, a protein is synthesized using the codons in
mRNA as a guide.