Topic 2 Molecular Biology Review
2.7
47. To replicate a molecule of DNA must unwind to expose the nitrogenous bases.
48. Helicase is the enzyme that breaks the hydrogen bonds to allow the unwinding.
49. The exposed bases of each strand are then paired with an available nucleotide by complementary base
pairing. The result is two strands where only one was first present.
50. DNA polymerase is an enzyme that allows the connection between nucleotides lined up by base-pairing.
51. This replication is called semi-conservative replication because each of the two formed molecules of DNA
contains one of the original strands and one new strand.
52. The daughter DNA strands are identical to one another thus preserving the genetic code.
53. RNA contains the 5C sugar ribose, is single stranded and contains the bases adenine, uracil, cytosine, and
guanine. Notice thymine is missing in RNA. RNA is a chain of RNA nucleotides connected by a covalent
bond between the phosphate of one nucleotide and the 3C of the next nucleotide.
54. DNA transcription involves the copying of the genetic code from DNA onto a strand of RNA.
55. This RNA strand is complementary to the DNA template strand.
56. The genetic code is actually composed of triplets of bases called codons. The codons are present on the
RNA formed during translation. Therefore, codons do not contain thymine.
57. The RNA formed during transcription is called messenger or mRNA. This mRNA carries the genetic code
out of the nucleus to the ribosomes in the cytoplasm.
58. It is at the ribosomes where the process of translation occurs. Translation is the process that leads to the
formation of polypeptides, proteins.
59. In the cytoplasm tRNA molecules contain anticodons. The tRNA anticodons pair with the mRNA codons
through base pairing. Because each tRNA with a particular anticodon carries a specific amino acid, the codon –
anticodon match allows a very specific protein or polypeptide to be produced.
60. A particular sequence on a DNA molecule that codes for a specific protein is called a gene. This gene will
always code for the formation of the same protein during the process of its transcription and translation.
61. There is a third type of RNA called ribosomal RNA (rRNA). This rRNA composes a significant part of the
ribosome which is the structure at which protein synthesis occurs via the process of translation.
62. The term translation is appropriate as during the process there is a change from the language of DNA
(nitrogenous base sequence) to the language of proteins (amino acid sequence).
2.7 DNA REPLICATION
**What is the central dogma of Biology?
**What is replication?
**Where does it take place?
**What is the end result?
**Why is DNA replication considered to be a semi-conservative process?
**What is the difference between the leading strand and the lagging strand?
**Which one (leading or lagging) is easier to copy? Why?
**State the role of each of the enzymes below in the replication process:
**helicase
**primase
**DNA polymerase III
**DNA polymerase I
**ligase
**What is the function of SSPs?
**How often are errors made in replication?
**What are Okazaki fragments?
**Be able to describe the synthesis of the leading strand as well as the lagging strand
**Which way does DNA polymerase III add nucleotides for the new strand (5’ to 3’ or 3’ to 5’)?
Transcription
**Discuss 3 major differences between DNA and RNA
**What are the 3 different types of RNA?
**What is the role of each? Where is each made?
**What is transcription?
**Where does it occur?
**What is the end result?
**Why does DNA have to make a messenger? Why can’t DNA leave the nucleus?
**transcription consists of 3 parts: ________________, elongation and ________________
**What enzyme unwinds and unzips the DNA and also adds nucleotides during transcription?
**Where does this enzyme come from?
**Which direction does this enzyme add nucleotides on the growing mRNA strand….5’ to 3’ or 3’ to 5’
**What is needed for the initiation process in order to get transcription started?
**What is this area on a DNA molecule called in most eukaryotes?
**Distinguish between the sense strand and anti-sense strand on the DNA during transcription
**Which strand should be exactly the same as the resultant mRNA and gets to put its feet up during the transcription
process?
**How does the enzyme know when to stop adding nucleotides?
**Before RNA gets shipped out of the nucleus, how is it “processed”?
**Why does mRNA have to be processed before it leaves the nucleus?
**Where does the mRNA go after it’s been transcribed?
**What is a codon?
Translation
**What is translation?
**Where does it occur?
**What is the final product?
**Draw a t-RNA showing where its amino acid and anti-codon are located
**What is the job/role of t-RNA?
**What is the purpose of the anti-codon?
**The super long name of the enzyme that attaches the amino acid to the t-RNA is called___________ ____
__________How many different ones of these enzymes are there?
**Just like transcription, translation occurs in 3 phases: ___________,___________and termination
**How does the initiation phase begin?
**During elongation, what happens to the tRNA in the “E” site on the ribosome?
**During elongation, where does an incoming tRNA come with its amino acid?
**Which is responsible for determining the amino acid that tRNA brings in….the codon on the mRNA or the anticodon on the tRNA?
**Just like in replication and transcription, the mRNA is read in the __ to __ direction
**When there is a tRNA on both the P and A site, describe what happens to the amino acids attached to them
**How is the process of translation terminated?
Complete the following.
39. What enzyme breaks the hydrogen bonds of DNA to produce separation of the two strands so that
replication may occur?
40. What enzyme is directly involved in the linking of nucleotides to produce the new strand of DNA in
replication?
41. List three differences between RNA and DNA.
RNA
1________________________________
2________________________________
3________________________________
42. In general, what happens in DNA transcription?
DNA
1___________________________
2___________________________
3___________________________
43. What type of RNA is produced by transcription?
44. Why must helicase be involved in transcription?
45. In general, how are replication and transcription similar?
46. In general, how are replication and transcription different?
47. On what molecule would one find a codon?___________
48. What is a codon?
49. What is the function of RNA polymerase?
50. What organelle does mRNA deliver the genetic code to?__________________
51. Name the process that results in protein synthesis.____________________
52. What is the function of tRNA in protein synthesis?
53. What part of the tRNA binds with the codon of the mRNA at the ribosome?
54. What does tRNA transport to the ribosomal-mRNA complex?___________________
55. The genetic code is said to be universal. What does this mean?
56. The genetic code is said to be degenerate. What does this mean?
57. How many different amino acids are there that make up proteins (polypeptides)?____
58. What type of bond allows the connection between the anti-codon of the tRNA and the codon of the mRNA
at the ribosome?_________________
59. How many subunits does a ribosome have?____________
60. Are there differences between prokaryotic and eukaryotic cell ribosomes?_______ Explain.
61. What is a third type of RNA involved in translation?________ What does it do?
62. What does the one gene/one polypeptide hypothesis state?
63. Follow the genetic code through protein synthesis.
DNA TTACGGCTA
mRNA_____________
tRNA anticodons_____________