Molecular Biology Review

A comprehensive set of flashcards covering key concepts related to molecular biology, genetics, and the processes of DNA replication, transcription, and translation.

What do changes at the molecular level imply in genetics?

Changes in the genetic code through mutations that affect transcription and translation, altering protein function and phenotype.

What is the role of the lac operon in gene regulation?

It shows how genes can be turned on or off based on the presence of lactose; the repressor protein blocks transcription when lactose is absent.

What are plasmids?

Double-stranded extra-chromosomal DNA molecules found in prokaryotes that replicate independently and carry nonessential genes.

How do prokaryotic and eukaryotic chromosomes differ?

Prokaryotic chromosomes are loosely organized in the cytoplasm with fewer proteins; eukaryotic chromosomes are found in the nucleus, tightly coiled around histones and associated with many proteins.

What are purines and pyrimidines?

Two types of nitrogenous bases in DNA and RNA; purines (adenine, guanine) have two rings, while pyrimidines (cytosine, thymine, uracil) have one ring.

What are the three types of frameshift mutations?

Insertion, deletion, and substitution (point mutations) which can lead to missense, nonsense, or silent mutations.

What are the structural differences between RNA and DNA?

RNA is single-stranded and made of ribose, while DNA is double-stranded and made of deoxyribose.

What are the main stages of DNA replication?

Initiation, unwinding, elongation, and termination.

What happens during transcription?

RNA polymerase binds to a promoter, unwinds DNA, elongates a new RNA strand, and terminates at a specific sequence.

What modifications occur to pre-mRNA in eukaryotic cells?

Addition of a 5’ cap, a poly-A tail, and splicing of introns.

What are the stages of translation?

Initiation, elongation, and termination.

What is negative regulation in gene expression?

A mechanism where a gene is repressed until repression is removed, preventing RNA polymerase from initiating transcription.

What is the difference between negative regulation and positive regulation?

Negative regulation actively represses genes until removal of repression, while positive regulation requires activators to turn genes on.

What are the four methods of genetic exchange in bacteria?

Transformation, transduction, conjugation, and transposition.

How does transformation occur in bacteria?

Bacteria take up DNA fragments from their environment and incorporate them into their genome.

What is transduction in bacterial genetics?

The transfer of DNA between bacteria via a virus.

What is conjugation in bacterial genetic exchange?

Direct DNA transfer between bacteria through cell-to-cell contact.

What is transposition in genetics?

Movement of DNA elements within or between DNA molecules.

What is the significance of genetic variation?

It increases options for survival in changing environments, allowing for natural selection and promoting adaptations.

What are some applications of plasmids in molecular biology?

Gene/molecular cloning, protein expression, and genetic engineering.

How does gel electrophoresis work?

DNA and RNA are subjected to an electric current in a gel, separating fragments by size.

Why is Taq polymerase important in PCR?

It allows DNA synthesis at high temperatures during PCR.

What does DNA sequencing provide?

It reveals the genetic code, mutations, and relationships among organisms.

What role does RNA polymerase play in transcription?

It binds to a promoter and synthesizes RNA by adding nucleotides complementary to the DNA template strand.

Define elongation in the context of transcription.

RNA polymerase reads the DNA template in the 5’-3’ direction and constructs a complementary RNA strand.

What is initiation in DNA replication?

The process where proteins bind to the origin of replication, starting the unwinding of the DNA double helix.

What function do histones serve in eukaryotic DNA?

They help in the coiling and organization of DNA into chromatin.

What causes a nonsense mutation?

A substitution that creates a premature stop codon, leading to truncated proteins.

How are Okazaki fragments formed?

They are short segments of DNA synthesized on the lagging strand during replication.

What distinguishes eukaryotic transcription from prokaryotic transcription?

Eukaryotic transcription involves the addition of a 5’ cap and poly-A tail and requires splicing.

What major role do transcription factors play?

They assist RNA polymerase in recognizing promoters to initiate transcription.

Define a missense mutation.

A substitution that results in a different amino acid being incorporated into the protein.

What is the significance of the 5’ cap and poly-A tail in eukaryotic mRNA?

They protect the mRNA from degradation and assist in ribosome binding during translation.

What happens when the ribosome reaches a stop codon?

A release factor binds, causing the polypeptide chain to be released.

How are mutations beneficial to organisms?

They can introduce adaptations that enhance survival in changing environments.

What does it mean for a gene to be 'turned on' in molecular biology?

It means that transcription is occurring, leading to the production of RNA and possibly a protein.

What is the function of ligase in DNA replication?

It joins Okazaki fragments on the lagging strand.