Untitled Deck Flashcards
What is the structure of DNA in prokaryotic cells?
Single chromosome (looped nucleus)
Prokaryotic DNA is typically circular and lacks a defined nucleus.
What is the structure of DNA in eukaryotic cells?
Many chromosomes in nucleus (46 in humans)
Eukaryotic DNA is linear and organized into multiple chromosomes.
What type of bond forms the backbone of DNA?
Phosphodiester linkage (covalently bonded)
The backbone consists of alternating phosphate and sugar groups.
What do nitrogenous bases in DNA represent?
The rungs of a ladder (hydrogen bonds)
The bases pair specifically (A-T and C-G) through hydrogen bonding.
What does the 3’ end of a DNA strand refer to?
Carbon 3 (has free hydroxyl group)
The 3’ end is critical for DNA replication and synthesis.
What does the 5’ end of a DNA strand refer to?
Carbon 5 (has free phosphate group)
The orientation of DNA strands is crucial during replication.
In what phase does DNA replication occur?
S phase of interphase
This phase ensures that each cell has a complete copy of DNA.
What is the semiconservative model of DNA replication?
Half of strand is new, half is old
This model was confirmed by the Meselson-Stahl experiment.
What was the Meselson-Stahl experiment designed to demonstrate?
DNA replication model
It showed that DNA replication is semiconservative.
What is the role of helicase in DNA replication?
Unwinds DNA by disrupting hydrogen bonds
This is essential for separating the strands for replication.
What do single-stranded binding proteins (SSB) do?
Keep separated DNA strands from reannealing
They prevent hydrogen bonds from forming between the strands.
What is the function of RNA primase in DNA replication?
Adds RNA primer to the 3’ end of both strands
This allows DNA polymerase to begin replication.
What is the role of DNA polymerase III?
Adds nucleotides to existing strand in 5’ → 3’ direction
It cannot initiate synthesis by itself, must have primer in place before it
What is the difference between the leading and lagging strands in DNA replication?
Leading strand has 1 primer, lagging strand has multiple primers
The lagging strand is synthesized in fragments known as Okazaki fragments.
What is the primary transcript in protein synthesis?
The RNA before any modifications, not ready to leave nucleus yet
Still has introns, no 5’ cap (modified guanine) or poly-A-tail
What are the three steps of transcription?
Initiation, Elongation, Termination
These steps occur in the nucleus of eukaryotic cells.
What modifications occur to mRNA before it leaves the nucleus?
- 5’ capping
- 3’ tailing
- Removal of introns
These modifications protect mRNA and facilitate its export.
What is the role of tRNA in translation?
Carries specific amino acid and has an anticodon loop
The anticodon is complementary to the mRNA codon.
What are the three ribosome bonding sites?
- A (acceptor) site
- P (peptide) site
- E (exit) site
Each site has a specific function in the translation process.
What happens when a stop codon enters the A site of the ribosome?
Translation terminates and polypeptide chain is released
Stop codons do not have complementary tRNAs and therefore don’t code for any amino acids
What is gene regulation?
Controls when and how genes are expressed
This is important for cellular efficiency and resource management.
What are housekeeping genes?
Genes that are constantly expressed
They are essential for basic cellular function.
What are the four levels of gene regulation?
- Transcriptional
- Post-transcriptional
- Translational
- Post-translational
Each level affects gene expression in different ways.
What is an operon?
Cluster of co-regulated genes in prokaryotes
Operons allow bacteria to regulate gene expression efficiently.
What is the function of the Lac operon?
Codes for proteins involved in lactose metabolism
It is an inducible operon that is turned on when lactose is present.
What is a point mutation?
Mistake affecting few nucleotides in a gene
It can lead to various outcomes, including silent, missense, or nonsense mutations.
What is a frameshift mutation?
Caused by insertion or deletion, misreads the sequence
It alters the reading frame of the genetic code.
What are mutagens?
Substances that can change DNA
They can lead to mutations and can be natural or synthetic.
What are restriction endonucleases?
Enzymes that cut double stranded DNA at specific sequences
They are used in genetic engineering and molecular cloning.
What is the difference between sticky ends and blunt ends in DNA fragments?
- Sticky ends: have hanging pieces of DNA
- Blunt ends: straight vertical cut
Sticky ends are more useful for ligation in recombinant DNA technology.
What is the sequence recognized by EcoRI?
GAATTC
EcoRI creates sticky ends by disrupting the bond between G and A on both strands.
What is the sequence recognized by SmaI?
CCCGGG
SmaI creates blunt ends.
What is the sequence recognized by HindIII?
AAGCTT
HindIII creates sticky ends.
What is the main difference between sticky ends and blunt ends?
Sticky ends have hanging pieces of DNA; blunt ends have a straight vertical cut.
What is recombinant DNA technology?
Combining genes of different organisms together to produce vaccines, hormones, or GMOs.
What type of DNA is commonly used in recombinant DNA technology?
Plasmid DNA
Plasmids are small and separate from the bacterial chromosome.
What are plasmids?
DNA molecules that can replicate independently of the bacterial chromosome.
What is a vector in genetic engineering?
A DNA molecule used as a vehicle to carry a particular DNA segment into a host cell.
What happens when human genes are inserted into plasmids?
They produce human proteins that can be purified and used for medical treatments.
What is the first step in DNA cloning (production of proteins)
Cutting of plasmid and gene, and insertion of gene
What enzyme is used to cut plasmids and genes in DNA cloning?
Restriction enzyme.
What is the purpose of ligase in DNA cloning?
To join the fragments of DNA together.
What is transformation in the context of DNA cloning?
Inserting plasmid back into bacteria.
How is antibiotic selection used in DNA cloning?
To identify bacteria that have taken up the plasmid with antibiotic resistance.
What is the role of T4 DNA ligase?
It can join sticky and blunt ends and is heat resistant.
What is PCR?
Polymerase chain reaction, a method to make millions of copies of a particular DNA sequence.
What are the three main steps of PCR?
- Denaturation
- Annealing
- Extension
At what temperature does denaturation occur in PCR?
~ 95℃.
At what temperature does annealing occur in PCR?
~ 55℃.
At what temperature does extension occur in PCR?
~ 72℃.
What polymerase is used in PCR and why?
Taq polymerase because it is heat resistant.
What is the purpose of gel electrophoresis?
To separate DNA fragments based on size.
How do DNA fragments move in gel electrophoresis?
With an electric current, moving towards the positive electrode.
What happens to shorter DNA fragments in gel electrophoresis?
They move farther because they encounter less resistance.
What is a DNA ladder?
A scale containing fragments of known sizes used to compare DNA fragment distances.
What is the function of the running buffer in gel electrophoresis?
To help conduct electricity.
What is the purpose of staining DNA in gel electrophoresis?
To make DNA fragments visible as dark bands.
What is the main component used to make gel in gel electrophoresis?
Agarose.
