exam 3 Flashcards
what do genes do
Genes pass down hereditary information and provide ‘instructions’ for how cells function, regulate, and form structures.
what are genes made of
DNA, which can code for amino acid sequences (proteins) or RNA (non-protein functions).
how is genetic information replicated?
DNA molecules replicate to produce two copies, distributed into each daughter cell.
what are transcription and translation
Transcription: RNA is synthesized by copying information from DNA using enzymes.
Translation: RNA’s base sequence directs the creation of a polypeptide.
when was DNA discovered and by who
1869, Friedrich Miescher
what evidence showed DNA is genetic material?
Griffith’s Experiment: Showed a “transforming principle” could convert R-strain bacteria into pathogenic S-strain.
Avery’s Experiment: Found DNA was the transforming substance by isolating nucleic acid from S-strain bacteria.
Hershey & Chase Experiment: Confirmed DNA, not protein, was injected into bacteria by phages.
what roles do bacteriophages play in genetic studies
infect bacteria, showing how DNA or RNA is the genetic material for replication and cell function.
what is the structure of DNA
double helix, with a sugar phosphate backbone on the outside, right handed helix (B-DNA)
What did Chargaff discover about DNA?
A=T and G=C in all DNA samples, with variation among species.
how does DNA replicate
The double helix separates, and each strand serves as a template for a new complementary strand.
how is DNA packaged in eukaryotes
DNA wraps around histones to form nucleosomes.
Nucleosomes coil into 30-nm chromatin fibers.
Chromatin fibers further fold into loops to form chromosomes.
Positively charged proteins that stabilize negatively charged DNA and organize it into chromatin.
histones
Loosely packed, transcriptionally active DNA.
euchromatin
Highly condensed, transcriptionally inactive DNA.
heterochromatin
what are the two types of repeated DNA sequences?
Tandemly repeated DNA and Interspersed repeated DNA
how are Interspersed repeated DNA arranged
Scattered sequences like LINEs and SINEs.
how is Tandemly repeated DNA arranged
Sequences arranged in rows, such as microsatellites and minisatellites.
what are transposons
Mobile genetic elements that can move and leave copies of themselves in the genome.
What is unique about mitochondrial and chloroplast DNA
Circular DNA with no histones.
Mitochondria: 16,569 bp encoding 37 genes.
Chloroplasts: ~120,000 bp encoding ~120 genes.
how do organelles depend on the nuclear genome
They rely on nuclear genes for most protein synthesis while encoding some of their polypeptides.
how can DNA melting temperature indicate stability
Higher Tm reflects tighter DNA binding due to more GC content and base stacking interactions
describe nucleic acid hybridization
A method where complementary sequences bind to identify specific nucleic acids, used in FISH.
what are histone modifications
Tags like methyl or acetyl groups alter chromatin structure, affecting gene expression.
explain histone codes
The combination of histone tags that regulate DNA activity and chromatin state.
two main products of genes
RNA transcription and protein
role of mRNA in protein synthesis
encodes instructions for translation and assembles amino acids into a polypeptide
how are genetic codes read
In triplets called codons, each coding for an amino acid or a stop signal.
key properties of the genetic code
Unambiguous, nonoverlapping, degenerate, and nearly universal.
What did Beadle and Tatum conclude in their experiments on bread mold?
The one gene–one enzyme hypothesis: each mutation disables one enzymatic step in a metabolic pathway.
What modification to the one gene–one enzyme hypothesis did Ingram propose?
One gene–one polypeptide, based on his study of sickle-cell anemia.
How many possible codon combinations exist in a triplet genetic code?
64
wobble hypothesis
Flexibility in tRNA anticodon pairing with more than one codon, especially at the third codon base.
What does AUG codon signify in translation?
The start codon, coding for methionine.
differences in eukaryotic and bacterial translation initiation
Bacteria use Shine-Dalgarno sequences and N-formylmethionine; eukaryotes use methionine and require more initiation factors.
polyribosome
cluster of ribosomes translating a single mRNA simultaneously.
what triggers termination in translation
Stop codons recognized by release factors.
what role do molecular chaperones play
They assist in proper folding of newly synthesized proteins and repair misfolded ones.
Hsp70 and Hsp60
Types of molecular chaperones that prevent aggregation and assist in folding of proteins.
How does a nonsense mutation affect translation?
Converts an amino acid codon to a stop codon, prematurely ending translation.
what is nonsense mediated decay
A process to destroy defective mRNAs containing premature stop codons.
what’s the energy cost of polypeptide elongation
Hydrolysis of at least 3 high-energy phosphoanhydride bonds per amino acid addition.
whats the central dogma of molecular biology
The central dogma describes the flow of genetic information: DNA → RNA → Protein
role of mRNA in protein synthesis
Carries genetic information from DNA to ribosomes.
role of rRNA in protein synthesis
Forms the core of ribosome structure and catalyzes protein synthesis.
role of tRNA in protein synthesis
Transfers amino acids to ribosomes during protein synthesis.
how does transcription differ in prokaryotes and eukaryotes?
Prokaryotes: Transcription and translation occur simultaneously without compartmentalization.
Eukaryotes: Transcription occurs in the nucleus; translation occurs in the cytoplasm.
the four stages of transcription are …
Binding, initiation, elongation, and termination.
enzyme that’s central to transcription and its purpose
RNA polymerase synthesizes RNA by adding complementary ribonucleotides to a DNA template.
how does bacterial transcription start
RNA polymerase binds to the promoter region, often containing conserved sequences like the -10 (TATAAT) and -35 (TTGACA) regions.
what happens during elongation in transcription
RNA polymerase moves along the DNA template, synthesizing RNA in the 5’ → 3’ direction while the DNA helix unwinds and rewinds.
what mechanisms terminate bacterial transcription
Rho-independent: A GC-rich hairpin loop followed by a U-rich sequence.
Rho-dependent: The rho protein unwinds the RNA-DNA hybrid to release RNA.
How many RNA polymerases are present in eukaryotes, and what do they synthesize?
3, RNA Pol I: rRNA.
RNA Pol II: mRNA, snRNA, microRNA.
RNA Pol III: tRNA, 5S rRNA.
What are the core promoter elements in eukaryotic transcription?
Initiator (Inr) sequence.
TATA box.
TFIIB recognition element (BRE).
Downstream promoter element (DPE).
How is transcription initiation different in eukaryotes?
Requires transcription factors (TFs) to assemble a preinitiation complex with RNA polymerase.
What modifications occur during RNA processing?
Addition of a 5’ cap.
Addition of a 3’ poly(A) tail.
Splicing to remove introns and join exons.
What is the function of the 5’ cap and poly(A) tail?
5’ Cap: Protects RNA from degradation and aids in ribosome binding.
Poly(A) Tail: Enhances mRNA stability and facilitates export to the cytoplasm.
What is RNA splicing
The removal of introns and joining of exons in pre-mRNA to form mature mRNA.
what structures catalyze splicing
Spliceosomes, composed of snRNPs and snRNA.
What are the two types of self-splicing introns?
Group I: Excised as linear fragments.
Group II: Excised as lariat structures.
What are examples of exceptions to the central dogma?
RNA viruses performing reverse transcription to synthesize DNA from RNA.
RNA-dependent RNA synthesis in some viruses.
what enzyme catalyzes reverse transcription
Reverse transcriptase.
What is the nucleolus?
nuclear structure where ribosome assembly occurs, containing DNA for rRNA production.
What are snoRNAs, and what do they do?
Small nucleolar RNAs guide chemical modifications like methylation during rRNA processing.
How are tRNAs processed?
Removal of 5’ leader sequence.
Replacement of the 3’ terminal sequence with CCA.
Addition of modified nucleotides.
What encloses eukaryotic chromosomes?
A nucleus bounded by a double-membrane nuclear envelope.
What mediates transport through the nuclear envelope?
Nuclear pores allow two-way transport between nucleoplasm and cytosol.
What is the nuclear lamina?
A thin, dense meshwork of fibers lining the inner surface of the inner nuclear membrane, providing mechanical strength.
what are nuclear pores
Specialized channels in the nuclear envelope where inner and outer membranes fuse, lined by a nuclear pore complex (NPC).
What is the function of the nuclear pore complex?
It facilitates the movement of small molecules, ions, and larger molecules like proteins and RNA.
How are large molecules transported through nuclear pores?
using nuclear localization signals (NLS) recognized by importins.
What is the Ran/Importin pathway?
A mechanism for nuclear import involving importins and the Ran-GTP cycle to transport proteins with NLS.
How does nuclear export work?
It involves exportins and Ran-GTP, with RNA often exported using adaptor proteins with nuclear export signals (NES).
Where are chromatin fibers located in the nucleus?
Each chromosome occupies its own distinct region called a chromosome territory
What is the main structural difference in nuclear support between plants and animals?
Plants and fungi lack nuclear lamins and use different proteins for nuclear structure.
What are the main phases of the cell cycle involving DNA replication?
DNA doubles during S phase, separated by G1 and G2 phases before mitosis.
how is DNA replicated
each strand of the double helix serves as a template for a complementary strand.
difference between leading and lagging strand synthesis
The leading strand is synthesized continuously; the lagging strand is synthesized in Okazaki fragments.
What is the role of primase in replication?
Synthesizing RNA primers to initiate DNA synthesis.
What enzymes unwind the DNA helix?
DNA helicases, stabilized by single-stranded DNA-binding proteins (SSBs).
How is supercoiling prevented during replication?
Topoisomerases create swivel points in DNA strands.
What is a replication origin in E. coli?
An AT-rich region called oriC, where replication begins.
How do eukaryotic origins of replication differ from prokaryotes?
Eukaryotic replication involves multiple replicons with AT-rich sequences.
What is the role of telomeres?
Protect chromosome ends by preventing loss of coding DNA during replication.
How does telomerase function?
It adds repeated DNA sequences to chromosome ends using an RNA template
What happens to telomeres in somatic cells?
They shorten over time, signaling cell aging and apoptosis.
What is the significance of selective gene expression in bacteria?
allows cells to be efficient by producing only what is needed, with related functions often clustered in operons that can be turned on or off.
two types of operons in bacteria?
Inducible operons (catabolic enzymes, turned on by substrate) and repressible operons (anabolic enzymes, turned off by end product).
How do allosteric repressor proteins regulate operons?
They bind to the operator to prevent transcription unless a substrate (inducible operons) or end product (repressible operons) changes their conformation.
What is substrate induction?
A process where enzymes like β-galactosidase are produced only in the presence of a substrate like lactose.
How does end-product repression work?
When the concentration of an end product (e.g., tryptophan) is high, the production of enzymes needed to synthesize it is repressed.
What is the lac operon, and what does it include?
A group of three genes (lacZ, lacY, lacA) with a promoter, operator, and regulatory gene (lacI) that controls lactose metabolism.
What does the lacI gene encode?
The lac repressor protein, which binds to the operator to block transcription of the lac operon.
How is the lac operon induced?
The inducer (allolactose) binds to the repressor, changing its shape so it cannot bind to the operator, allowing transcription to occur.
What role does cyclic AMP (cAMP) and CAP play in the lac operon?
When glucose is low, cAMP binds to CAP, which activates transcription by enhancing RNA polymerase binding to the promoter.
What is catabolite repression?
mechanism where the presence of glucose suppresses the lac operon by reducing cAMP levels.
How is the trp operon regulated?
It is repressed by tryptophan (corepressor), which activates the repressor protein to block transcription.
What is attenuation in the trp operon?
A regulatory mechanism where leader mRNA forms hairpin loops based on tryptophan levels, controlling transcription continuation.
What happens at high tryptophan levels in the trp operon?
Regions 3 and 4 form a terminator hairpin, stopping transcription.
What happens at low tryptophan levels in the trp operon?
Regions 2 and 3 form an antiterminator hairpin, allowing transcription to proceed
What are riboswitches?
mRNA regions that bind small molecules to alter their shape, regulating transcription or translation.
What role do CRISPR sequences play in bacterial immunity?
They incorporate viral DNA into spacers, directing Cas proteins to cleave invader DNA during future attacks.
What distinguishes eukaryotic gene regulation from bacterial regulation?
Eukaryotic regulation is more complex due to multicellularity and differentiation, involving chromatin remodeling, histone modifications, and DNA methylation.
the five levels of eukaryotic gene control?
- Genome, 2. Transcription, 3. RNA processing/export, 4. Translation, 5. Post-transcriptional control.
What is genomic equivalence?
a concept that all cells in an organism have the same DNA, though only specific genes are expressed based on cell type.
What is the significance of nuclear transplantation experiments?
showed that differentiated nuclei can direct the development of an entire organism, demonstrating totipotency.
difference between pluripotent and multipotent stem cells?
Pluripotent stem cells can become any cell type except placental cells, while multipotent stem cells can differentiate into several but limited types.
