DNA Replication And Protein Synthesis Flashcards
What are the main enzymes involved in DNA replication and their functions?
Helicase: Unzips the DNA double helix.
Primase: Synthesizes RNA primers.
DNA Polymerase: Adds complementary nucleotides and proofreads.
Ligase: Joins Okazaki fragments on the lagging strand.
Topoisomerase: Relieves supercoiling tension.
How do the leading and lagging strands differ during DNA replication?
Leading Strand: Synthesized continuously in the 5’ to 3’ direction.
Lagging Strand: Synthesized discontinuously in fragments (Okazaki fragments) because replication occurs in the opposite direction of the fork.
What does it mean that DNA replication is semi-conservative?
Each new DNA molecule consists of one original (parental) strand and one newly synthesized strand.
What is the origin of replication?
A specific DNA sequence where replication begins. Prokaryotes have one origin, while eukaryotes have multiple origins of replication.
How does DNA polymerase ensure accuracy during replication?
DNA polymerase proofreads each newly added nucleotide and removes errors through exonuclease activity.
In which direction does DNA synthesis occur, and why?
DNA synthesis occurs in the 5’ to 3’ direction because DNA polymerase can only add nucleotides to the 3’ end of a growing strand.
Why are RNA primers necessary for DNA replication?
DNA polymerase cannot initiate synthesis on its own; RNA primers provide a starting point with a free 3’ hydroxyl group.
What are telomeres, and why are they important?
Telomeres are repetitive sequences at the ends of eukaryotic chromosomes that protect against the loss of important genetic information during replication.
What is telomerase, and what role does it play?
Telomerase is an enzyme that extends telomeres in certain cells, like germ cells and stem cells, ensuring the complete replication of chromosome ends.
How does DNA replication differ in prokaryotes and eukaryotes?
Prokaryotes: Single origin of replication; circular DNA.
Eukaryotes: Multiple origins of replication; linear DNA.
What are promoters and terminators in transcription?
Promoters: DNA sequences where RNA polymerase binds to initiate transcription.
Terminators: DNA sequences that signal RNA polymerase to stop transcription.
What are key characteristics of the genetic code?
Universal: Same in almost all organisms.
Redundant: Multiple codons can code for the same amino acid.
Non-overlapping: Codons are read in sequence, without overlap.
What are the main sites on the ribosome during translation?
A site: Holds the incoming tRNA carrying the next amino acid.
P site: Holds the tRNA with the growing polypeptide chain.
E site: Exit site for discharged tRNAs.
What are the main differences between transcription and translation?
Transcription: DNA → RNA, occurs in the nucleus (eukaryotes).
Translation: RNA → Protein, occurs in the cytoplasm (on ribosomes).
What are the types of RNA and their roles?
mRNA: Carries genetic code from DNA to ribosome.
tRNA: Brings amino acids to ribosome.
rRNA: Structural and catalytic component of ribosomes.
snRNA: Involved in RNA splicing.
What are post-translational modifications, and why are they important?
Changes to the protein after translation, such as folding, phosphorylation, or glycosylation, that affect its function and activity.
What is an operon, and how does it function?
An operon is a cluster of genes under the control of a single promoter.
Example: Lac Operon (inducible, active when lactose is present).
What are the start and stop codons?
Start Codon: AUG (methionine).
Stop Codons: UAA, UAG, UGA (signal termination of translation).
What are mutagens, and how do they affect DNA?
Mutagens are agents like chemicals, radiation, or viruses that cause mutations by altering DNA structure or sequence.
How does gene expression differ in eukaryotes and prokaryotes?
Prokaryotes: Transcription and translation occur simultaneously; no RNA processing.
Eukaryotes: Transcription occurs in the nucleus; translation in the cytoplasm; involves mRNA processing.
What are chaperone proteins, and what is their role in protein synthesis?
Chaperone proteins assist in the proper folding of newly synthesized proteins to ensure functionality.
How do mutations affect protein synthesis?
Silent Mutation: No effect on protein.
Missense Mutation: Alters one amino acid.
Nonsense Mutation: Creates a stop codon.
Frameshift Mutation: Shifts the reading frame, altering downstream amino acids.
What is epigenetics, and how does it affect gene expression?
Epigenetics involves modifications to DNA (like methylation) or histones that affect gene expression without altering the DNA sequence.
