Chapter 11 Powerpoint (Review) Flashcards
What is the significance of Jacques Monod’s quote regarding E. coli and elephants?
It highlights that basic molecular mechanisms are remarkably similar across all life forms.
What is the genetic material for all cells?
DNA
What is a genome?
The entire DNA content of an organism, usually divided among chromosomes.
What are the fundamental processes that follow a common blueprint across life forms?
- DNA replication
- Gene expression
Define genotype.
The sum of all genes in an organism.
Define phenotype.
The observable traits of an organism.
What is semiconservative replication?
DNA unwinds, with each old strand serving as a template for a new strand.
What enzyme unwinds DNA during replication?
Helicase
What is the role of DNA polymerase III?
It adds nucleotides in the 5’→3’ direction during DNA replication.
What is the difference between leading and lagging strands?
- Leading Strand: Synthesized continuously
- Lagging Strand: Synthesized in Okazaki fragments
What are telomeres?
Noncoding repeats at the ends of eukaryotic chromosomes that protect coding regions.
What are the three main RNA polymerases in eukaryotes?
- RNA polymerase I
- RNA polymerase II
- RNA polymerase III
What is the central dogma of molecular biology?
DNA → RNA → Protein
What is a codon?
A 3-nucleotide sequence on mRNA that specifies an amino acid.
What is a silent mutation?
A mutation that does not change the amino acid sequence.
What is the purpose of the Shine-Dalgarno sequence in prokaryotes?
It helps the ribosome identify the start codon on mRNA.
What are the stages of translation?
- Initiation
- Elongation
- Termination
What is horizontal gene transfer (HGT)?
The transfer of genes between organisms of the same generation.
What are the three major modes of horizontal gene transfer?
- Transformation
- Transduction
- Conjugation
What is the role of the operator in an operon?
It is a sequence where a repressor can bind to block transcription.
What happens in a repressible operon?
It is usually on but can be turned off by high levels of the end product.
What is the function of telomerase?
It extends telomeres in germ cells and some stem cells.
What is proofreading in DNA replication?
The ability of DNA polymerase to correct errors as it elongates.
What is a frameshift mutation?
Insertion or deletion of nucleotides that alters the reading frame.
What is the role of ribosomes in protein synthesis?
They translate mRNA into proteins by facilitating the binding of tRNA.
What does the term ‘mutation’ refer to?
A heritable change in the DNA sequence.
What is the difference between an inducer and a repressor in gene regulation?
- Inducer: Activates transcription
- Repressor: Prevents transcription
What is the role of RNA primase?
Synthesizes short RNA primers needed for DNA polymerase to start replication.
Fill in the blank: The _______ is the structural unit of DNA.
Chromosome
Fill in the blank: _______ mutations change an amino acid codon to a stop codon.
Nonsense
True or False: All genes are turned on all the time in a cell.
False
What is a plasmid?
Extra, small circular DNA that can carry beneficial genes.
What is the function of ligase in DNA replication?
Seals the final nicks in the sugar-phosphate backbone.
What is a Frameshift Mutation?
Insertion/deletion of non-multiple-of-3 nucleotides, altering the entire downstream reading frame.
Define Mutagen.
Any agent (chemical or physical) that increases mutation rate.
What is a Thymine Dimer?
Two adjacent thymines in DNA covalently bonded, often caused by UV.
What is a Carcinogen?
Substance that can lead to cancer, often by causing mutations.
What is Proofreading in DNA replication?
DNA pol’s ability to check and correct mismatched bases during replication.
What is Mismatch Repair?
Mechanism to correct mismatches missed by proofreading, shortly after replication.
What is Excision Repair?
Cutting out and replacing damaged DNA regions (e.g., nucleotide excision for dimers).
Define Photoreactivation.
Light-based repair of thymine dimers via photolyase (not in humans).
What is Horizontal Gene Transfer (HGT)?
Transfer of genetic material between organisms in the same generation.
What is Transformation?
Uptake of free (naked) DNA from the environment by a cell.
What is Transduction?
DNA transfer between cells mediated by a bacteriophage virus.
What is Conjugation?
DNA transfer through direct cell contact (often a pilus) in bacteria.
Define Operon.
A set of functionally related genes regulated together under one promoter/operator.
What is a Promoter?
DNA region where RNA polymerase binds to initiate transcription.
What is an Operator?
DNA region where repressors bind, typically blocking transcription.
Define Repressor.
Regulatory protein that turns off transcription when bound to the operator.
What is an Activator?
Regulatory protein that increases transcription by helping RNA pol bind.
What is an Inducer?
Small molecule that can turn on an operon (often by inactivating a repressor).
What is the trp Operon?
Repressible operon for tryptophan synthesis; turned off when tryptophan is high.
What is the lac Operon?
Inducible operon for lactose metabolism; turned on in the presence of lactose (and low glucose).
Define Polycistronic.
mRNA encoding multiple proteins (typical in prokaryotes).
Define Monocistronic.
mRNA encoding a single protein (typical in eukaryotes).
What are Introns?
Noncoding sequences in eukaryotic genes that get spliced out.
What are Exons?
Coding sequences that remain in mRNA after introns are removed.
What is a 5’ Cap?
A modified guanine added to the 5’ end of eukaryotic mRNA for stability and ribosome binding.
What is a Poly-A Tail?
Long stretch of adenine nucleotides added to the 3’ end of eukaryotic mRNA, aiding stability and export.
Define Telomere.
Noncoding, repetitive DNA at eukaryotic chromosome ends, protecting coding sequences.
What is Telomerase?
Enzyme that extends telomeres (active in germ cells, some stem cells).
What is a Sigma (σ) Factor?
A bacterial protein that directs RNA pol to specific promoters.
What is fMet?
Formyl-methionine in bacterial translation’s start codon (modified methionine).
What is a Release Factor?
Protein binding the stop codon, terminating translation.
What does Jacques Monod’s quote imply?
Basic genetic mechanisms (DNA replication, transcription, translation) are conserved across all life.
What are the functions of DNA?
- Storage: Passes genetic information to offspring
- Replication: Copied with high accuracy to preserve integrity
- Gene Expression: Directs protein synthesis via transcription (DNA → RNA) and translation (RNA → protein).
What is the Central Dogma of molecular biology?
Flow: DNA → RNA → Protein.
What is the difference between Genotype and Phenotype?
- Genotype: All genes in a cell
- Phenotype: Observable traits from expressed proteins.
What is Semiconservative Replication?
Each new DNA molecule has 1 parental strand + 1 new strand.
What is the role of Helicase in DNA replication?
Unzips DNA by breaking hydrogen bonds.
What does DNA Polymerase III do?
Adds nucleotides (5’→3’ direction).
What is the function of Primase?
Makes RNA primers for DNA Pol III.
What does Ligase do in DNA replication?
Seals gaps between Okazaki fragments.
How many origins of replication do Prokaryotes have?
1 origin (e.g., E. coli’s oriC).
How many origins of replication do Eukaryotes have?
30,000–50,000 origins per chromosome.
What is the speed of DNA replication in Prokaryotes?
~1,000 nucleotides/sec.
What is the speed of DNA replication in Eukaryotes?
~100 nucleotides/sec.
What are Okazaki Fragments?
Short DNA segments on lagging strand.
What is the role of Topoisomerase IV?
Separates interlocked circular DNA.
What are the steps in RNA Transcription?
- Initiation: RNA polymerase binds promoter
- Elongation: RNA synthesized 5’→3’; DNA rewound behind
- Termination: RNA released; polymerase detaches.
What type of RNA polymerase do Eukaryotes have?
3 types (I, II, III).
What type of mRNA do Prokaryotes produce?
Polycistronic (multiple genes).
What type of mRNA do Eukaryotes produce?
Monocistronic (single gene).
Define Codon.
3-nucleotide sequence (64 total; 61 code amino acids, 3 are stop codons).
What is the Start Codon?
AUG (methionine).
What is the Wobble Position?
3rd base in codon (flexible pairing).
What are the steps in Translation?
- Initiation: Ribosome assembles on mRNA; initiator tRNA binds AUG
- Elongation: Amino acids added via peptidyl transferase
- Termination: Stop codon triggers release.
What is a Silent Mutation?
No amino acid change (same codon).
What is a Missense Mutation?
Altered amino acid (e.g., sickle cell anemia).
What is a Nonsense Mutation?
Premature stop codon.
What are the causes of mutations?
- Spontaneous: DNA replication errors
- Induced: Mutagens (e.g., UV → thymine dimers, chemicals → base analogs).
What is Nucleotide Excision Repair?
Removes thymine dimers.
What is the mnemonic for Horizontal Gene Transfer (HGT)?
Three Transfer Channels (Transformation, Transduction, Conjugation).
What is the role of a Spliceosome?
Removes introns from pre-mRNA.
What is RNA Splicing?
Removal of introns and joining exons.
What is Vertical Gene Transfer?
Inheritance from parent to offspring.
