DNA Structure
Which nitrogenous bases are purines and which are pyrimidines?
The nitrogenous bases are grouped into two categories:
Purines (double-ring structure):
Pyrimidines (single-ring structure):
Easy way to remember:
Describe the role of helicase in DNA replication.
Helicase's job is to unwind and unzip DNA by breaking the hydrogen bonds between the two strands so they can be copied.
Where in the cell does transcription occur?
nucleus
Where in the cell does translation occur?
ribosome
If a DNA strand had the sequence:
ATG CCT GAA
What would the complementary DNA strand be?
TAC GGA CTT
The _______-_________ backbone of DNA is held together by ______ bonds. The nitrogenous bases are held together by ______ bonds.
sugar-phosphate, covalent, hydrogen.
What is role of DNA polymerase in DNA replication?
Add complimentary base pairs and proofread as it goes.
Describe an overview of what happens during transcription.
Transcription is the process in which RNA polymerase copies genetic information from DNA into mRNA inside the nucleus. This happens because DNA cannot exit the nucleus but mRNA can.
Describe an overview of what happens during translation.
During translation, the mRNA travels to a ribosome, which reads the mRNA codons (three-base sequences). The ribosome matches each codon with the correct tRNA carrying a specific amino acid. As the ribosome moves along the mRNA, the amino acids are assembled in the correct order and joined together by peptide bonds. This forms a growing polypeptide chain. When the ribosome reaches a stop codon, translation ends, and the completed polypeptide chain folds into a functional protein.
Codons are read in sections of _, and are based off of the ____ sequence.
3, mRNA.
What are the three main differences between DNA and RNA?
Sugar
Nitrogen Base
Structure
Why is DNA replication called a semi-conservative process?
DNA replication is semi-conservative because each new DNA molecule is made of one old strand and one new strand.
What enzyme if responsible for adding bases during transcription?
RNA polymerase
When reading the mRNA, what is one sequence that would cause the termination of translation?
Use this DNA sequence to answer the following question:
TAC GGT ACA TTT
An anticodon of the tRNA that carries the last amino acid will be:
UUU
Guanine makes up 24% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be adenine?
26%
Explain the differences between DNA replication in prokaryotic and eukaryotic cells.
What happens to the single-stranded mRNA during the post-transcriptional modifications?
Introns, or non-coding regions, are removed or spliced out. Exons are glued together. A cap and tail is added so the mRNA is read in the correct direction.
What has to occur after translation to turn the polypeptide chain into a functional protein?
folding and modifications by the ER/golgi.
mRNA: AUG GCU CCA UAC
What is the DNA template strand that this mRNA was transcribed from?
What are the tRNA anticodons that would pair with each mRNA codon?
1. DNA Template Strand: TAC CGA GGT ATG
2. tRNA Anticodons:
tRNA anticodon sequence: UAC CGA GGU AUG
3. Amino Acids:
Amino acid sequence:
Methionine - Alanine - Proline - Tyrosine
The structural unit of DNA is called a _______. This is made of the following three components:
nucleotide, deoxyribose sugar, phosphate, nitrogenous base.
Use the following terms to explain how DNA replication occurs: RNA primase, helicase, DNA polymerase, leading strand, lagging strand, Okazaki fragments, ligase.
During DNA replication, helicase first unwinds and unzips the DNA double helix by breaking the hydrogen bonds between the base pairs. This creates two template strands.
Next, RNA primase adds short RNA primers to the exposed DNA strands. These primers provide a starting point for DNA polymerase.
DNA polymerase then adds complementary nucleotides to build new DNA strands in the 5' → 3' direction. The leading strand is synthesized continuously toward the replication fork. The lagging strand is synthesized discontinuously away from the replication fork in short segments called Okazaki fragments.
After the Okazaki fragments are formed, DNA polymerase replaces the RNA primers with DNA nucleotides. Finally, ligase joins the Okazaki fragments together, creating one continuous DNA strand.
Describe the role of each type of RNA in protein synthesis.
mRNA:
tRNA:
rRNA:
mRNA (messenger RNA): Carries the genetic instructions copied from DNA to the ribosome, where proteins are made.
tRNA (transfer RNA): Brings the correct amino acid to the ribosome and matches its anticodon to the mRNA codon.
rRNA (ribosomal RNA): Makes up part of the ribosome and helps assemble amino acids together to form a polypeptide chain.
Explain the mechanism of tRNA. How is it able to bind to mRNA and based off of this ability how is it able to create polypeptide chains?
tRNA creates polypeptide chains because its anticodon can bind to complementary mRNA codons, allowing it to deliver the correct amino acids to the ribosome, where they are joined together into a protein.
What would be the code for a tRNA anticodon designed to grab aspartic acid?
CUA or CUG