DNA, RNA & Protein Synthesis (College Board AP® Biology): Flashcards
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Define nucleotide.
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Define nucleotide.
Nucleotide is the monomer of nucleic acids, made up of a pentose sugar, a phosphate group and a nitrogenous base.
Define plasmid.
Plasmid is a small, circular molecule of DNA that is separate from the main chromosome and can be found in both prokaryotes and eukaryotes.
Which nucleic acid is the primary source of heritable information, and what is the exception?
DNA is the primary source of heritable information.
In some cases, such as certain viruses, RNA carries the genetic information instead.
How is DNA packaged in eukaryotic cells?
As multiple linear chromosomes, which are condensed by winding the DNA around histones and associated proteins.
How is DNA packaged in prokaryotic cells?
Most DNA is carried in a single, circular chromosome.
Prokaryotes also contain plasmids; small, circular DNA molecules separate from the chromosome.
The pentose sugar found in DNA is , whereas the sugar found in RNA is ribose.
The pentose sugar found in DNA is deoxyribose, whereas the sugar found in RNA is ribose.
Which nitrogenous bases are purines, and what is their structure?
Adenine (A) and guanine (G) are purines.
They have a double-ring structure.
Which nitrogenous bases are pyrimidines, and what is their structure?
Cytosine (C), thymine (T) in DNA and uracil (U) in RNA are pyrimidines.
They have a single-ring structure.
True or False?
In DNA, adenine pairs with cytosine.
False.
Adenine pairs with thymine (or uracil in RNA), and cytosine pairs with guanine.
Within double-stranded regions, complementary bases join together via bonds.
Within double-stranded regions, complementary bases join together via hydrogen bonds.
Why does a purine always pair with a pyrimidine?
Pairing a double-ring purine with a single-ring pyrimidine creates base pairs of equal length, keeping the width of the molecule constant.
True or False?
DNA forms a double-stranded helix, while RNA is single-stranded.
True.
DNA forms a double-stranded helix, while RNA is single-stranded, although it can fold to form double-stranded regions.
Give two features that make DNA well suited to storing genetic information.
The deoxyribose sugar makes DNA a stable molecule
Complementary base pairing means each strand can be determined from the other, allowing easy replication
Many combinations of the four bases allow a large volume of information to be stored
True or False?
Specific nucleotide base pairing has been conserved through evolution.
True.
Specific base pairing has stayed the same across evolutionary time and is the same between different groups of organisms.
Define DNA replication.
DNA replication is the process by which a DNA molecule is copied accurately to produce two identical molecules, ensuring continuity of hereditary information between generations.
Define semiconservative replication.
Semiconservative replication is a form of replication in which each new DNA molecule contains one original strand and one newly synthesized strand.
Define template strand.
Template strand is the original strand of DNA that serves as the template for building a new, complementary strand.
DNA replication takes place during the phase of the cell cycle.
DNA replication takes place during the S phase of the cell cycle.
In which direction is a new DNA strand synthesized?
In the 5' to 3' direction, because DNA polymerase can only add nucleotides to the 3' end of the growing strand.
What is the role of helicase in DNA replication?
Helicase unwinds the DNA strands, exposing the template strand.
What is the function of topoisomerase during DNA replication?
It relaxes the supercoiling that builds up in the DNA in front of the replication fork.
Why does DNA polymerase require RNA primers?
RNA primers provide a region to which DNA polymerase can bind in order to begin synthesizing a new strand.
What does DNA polymerase do during replication?
It synthesizes new DNA strands by joining adjacent nucleotides to form a new sugar-phosphate backbone.
How does synthesis of the leading strand differ from the lagging strand?
The leading strand is synthesized continuously.
The lagging strand is synthesized discontinuously in short fragments.
What is the role of ligase in DNA replication?
Ligase joins the fragments of DNA on the lagging strand to complete the new DNA molecule.
True or False?
DNA replication is a conservative process in which both strands of each new molecule are newly made.
False.
DNA replication is semiconservative — each new molecule keeps one original strand and gains one newly synthesized strand.
What is the role of messenger RNA (mRNA)?
To carry information from DNA in the nucleus to the ribosome in the cytoplasm, in the form of codons.
Define transfer RNA (tRNA).
Transfer RNA (tRNA) is a single-stranded RNA molecule that binds a specific amino acid at one end and has an anticodon that base pairs with the corresponding mRNA codon during translation.
What is the function of ribosomal RNA (rRNA)?
rRNA combines with proteins to form ribosomes — it is a functional building block of the ribosome.
True or False?
The function of an RNA molecule is determined by its base sequence and resulting structure.
True.
Both the sequence of RNA bases and the three-dimensional structure the molecule folds into determine what job the RNA does.
Define transcription.
Transcription is the process of converting the information encoded in a DNA template strand into a molecule of mRNA.
During transcription, the enzyme joins adjacent RNA nucleotides to form the sugar-phosphate backbone of the mRNA.
During transcription, the enzyme RNA polymerase joins adjacent RNA nucleotides to form the sugar-phosphate backbone of the mRNA.
How many strands of DNA does RNA polymerase use as a template during transcription?
A single template strand of DNA is used to direct the inclusion of bases in the newly formed RNA molecule.
In which direction does RNA polymerase synthesize mRNA, and in which direction does it read the template DNA strand?
RNA polymerase synthesizes mRNA in the 5' to 3' direction by reading the template DNA strand in the 3' to 5' direction.
True or False?
DNA polymerase is the enzyme responsible for joining RNA nucleotides during transcription.
False.
RNA polymerase joins RNA nucleotides during transcription; DNA polymerase joins DNA nucleotides during DNA replication.
What effect does adding a poly-A tail have on an mRNA molecule?
The poly-A tail makes the mRNA more stable, increasing the time it can spend in the cytosol before it degrades.
The addition of a to the 5' end of the mRNA helps with ribosomal recognition.
The addition of a GTP cap to the 5' end of the mRNA helps with ribosomal recognition.
Define introns.
Introns are noncoding regions present in eukaryotic pre-mRNA that are removed during processing, leaving behind only the coding regions (exons).
Define alternative splicing.
Alternative splicing is the joining of exons in different combinations, allowing more than one mature mRNA molecule to be produced from a single gene.
True or False?
mRNA modifications such as adding a poly-A tail and a GTP cap occur in eukaryotic cells.
True.
In eukaryotic cells the mRNA transcript undergoes a series of enzyme-mediated modifications, including addition of a poly-A tail, addition of a GTP cap, and removal of introns.
Define translation.
Translation is the process by which the genetic code carried in an mRNA molecule is converted into a polypeptide.
Define codon.
Codon is a sequence of three nucleotides on an mRNA molecule that encodes a specific amino acid.
Where in the cell does translation take place?
On ribosomes, which are found:
in the cytoplasm of both prokaryotic and eukaryotic cells
on the cytoplasmic surface of the rough endoplasmic reticulum in eukaryotic cells
What are the three main stages of translation?
Initiation
Elongation
Termination
The start codon AUG codes for the amino acid .
The start codon AUG codes for the amino acid methionine.
What interaction initiates translation?
The rRNA in the ribosome interacts with the mRNA at the start codon (AUG).
What is the role of tRNA during elongation?
Each tRNA brings the correct amino acid, specified by the codon on the mRNA, to the ribosome. The tRNA's anticodon is complementary to the mRNA codon.
During elongation, a bond forms between adjacent amino acids.
During elongation, a peptide bond forms between adjacent amino acids.
What signals that translation should stop?
A stop codon on the mRNA signals termination, at which point the completed polypeptide is released from the ribosome.
True or False?
Many amino acids are encoded by more than one codon.
True.
The genetic code is redundant, so several different codons can specify the same amino acid (e.g., GAU and GAC both code for aspartic acid).
True or False?
In prokaryotes, transcription and translation can occur simultaneously.
True.
Prokaryotes have no nuclear membrane separating the processes, so a ribosome can translate one end of an mRNA while the other end is still being transcribed.
Why is the near-universal genetic code considered evidence of common ancestry?
Nearly all living organisms use the same genetic code, suggesting they all descend from a common ancestor.
How does the flow of genetic information differ in retroviruses?
Retroviruses use reverse transcriptase to copy their RNA genome into DNA. This DNA integrates into the host genome and is then transcribed and translated to assemble new viral progeny.
Define retrovirus.
Retroviruses are a group of viruses that have RNA as their genetic material and use the enzyme reverse transcriptase to convert that RNA into DNA inside a host cell.
Define reverse transcriptase.
Reverse transcriptase is the enzyme that copies a retrovirus's RNA genome into DNA, allowing the alternate flow of information from RNA to DNA.
What type of molecule is the genetic material of a retrovirus?
RNA.
How is a retrovirus's flow of genetic information different from the usual flow?
The usual flow is DNA → mRNA → protein.
A retrovirus has an alternate flow in which RNA is first converted to DNA (RNA → DNA) before transcription and translation occur.
Why must a retrovirus convert its RNA into DNA after infecting a host cell?
So that the resulting DNA can be inserted into the host cell genome, where it can then be transcribed and translated to make new viral proteins.
In a retrovirus, RNA is converted into DNA by the enzyme .
In a retrovirus, RNA is converted into DNA by the enzyme reverse transcriptase.
Once made, the viral DNA integrates into the host cell , where it is transcribed and translated.
Once made, the viral DNA integrates into the host cell genome, where it is transcribed and translated.
After a retrovirus's DNA is integrated into the host genome, what does the host cell do with it?
The host cell transcribes and translates the integrated viral DNA, assembling new viral progeny (new virus particles).
True or False?
Retroviruses store their genetic information as DNA.
False.
Retroviruses store their genetic information as RNA, which must be converted to DNA by reverse transcriptase before it can be used by the host cell.
True or False?
HIV is an example of a retrovirus.
True.
HIV is a retrovirus; it has an RNA genome that is converted into DNA by reverse transcriptase.
In general, how are viral proteins produced once a virus has infected a host cell?
The virus inserts its genetic material into the host cell genome, and the host cell then carries out transcription and translation to make the viral proteins.
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