Quan Flashcards
• Prokaryotes (how unique from eukaryotes)
o Lack of defined nucleus
o Poorly developed organelles
o Transcription & translation may be concurrent
o Polycistronic: referring to mRNA carrying information for the synthesis of more than one protein
• Eukaryotes (how unique from prokaryotes)
o Highly defined nucleus
o Well developed organelles
o Separate mRNA processing
o Monocistronic: one gene controls one protein
In eukaryotes, one must consider….
- DNA is in chromatin
- There are three RNA polymerases versus one
- The initial transcript requires processing before it is functional mRNA
- mRNA synthesized in nucleus and translated in cytoplasm so transcription-translation coupling does not occur
Describe Chromatin structure
- Nucleosomes
* DNA wrapped around protein, termed chromatin
4 Characteristics of Heterochromatin
- The most tightly packaged form of DNA.
- Transcriptionally silent
- Different from cell to cell
- Modification of histone tails can tighten or loosen the nucleosome
Three major Modification of Histone Proteins
- Acetylation
- Phospharylation
- Methylation
Types of Polymerases (prok and euk)
• Prokaryotes
o One kind of RNA polymerase
• Eukaryotes
o Have Polymerase II
Describe how/why RNA polymerase binds to the promoter region of DNA
- Promoter: a DNA sequence that determines the site of transcription initiation for an RNA polymerase.
- It is non-coding region
Why can either DNA strand may serve as the template?
• The promoter is asymmetric. Therefore the polymerase will always bind in the proper orientation
• It can only synthesize in the 5’ to 3’ direction.
o The template will be 3’ to 5’ direction.
Phases of mRNA synthesis
- Initiation -> Elongation -> termination
* In prokaryotes, make a ring structure that would bump the RNA polymerase
Not all promoters are alike…how so/why?
• Align 13 different σ70 promoters
o Consensus sequence at -10
o Consensus sequence at -35
o 16-18 bp between them
Describe how Sigma factors act as initiation factors
• Different sigma factors recognize different consensus promoter sequences
• Different “strength” of promoter determined by Pol interaction with promoter.
o Strong = produce more RNA
o Weaker = less amount of RNA
What happens to cause Transcriptional Termination?
• Stem-loop formation
o Presents only in prokaryotes
o Rich G-C bonds
What is transcriptional translational coupling?
- Many polymerase simultaneously transcribing the gene
- Ribosomes simultaneously translating protein
- Does not occur in eukaryotes
Prokaryotes regulate genes by repression and induction…describe the classic example of the trp operation
• Situation
o If tryptophan is present its synthesis in unnecessary
o If tryptophan is absent its synthesis is necessary.
• Under negative control
o A trans-acting repressor binds to the cis-acting operator to turn off transcription
o Repressors bind to DNA sequences operators, which overlap the promoter region.
o A bound repressor interferes with binding of RNA polymerase and transcription initiation.
What is the trp operon?
• Operon: contiguous genes transcribed as a single mRNA
• Here, all code for enzymes necessary for tryptophan (trp)
• Polycistronic:
o DNA: one promoter and five genes
The lac operon is under both negative and positive transcriptional controls…describe the situation
• Situation
o Glucose + = glucose metabolism
o Glucose +, lactose + = glucose metabolism
o Glucose -, lactose + = lactose metabolism
Decribe B-galactosidase’s role with the the lac operon
• Β – galactosidase, is the enzyme that break down lactose into galactose and glucose.
• the lac operon transcription-control region
o positive control: CAP protein
o Negative control: repressor
• Positive control of the lac operon by glucose
o CAP needed for efficient binding of pol to promoter
Definition of genetics
The study of heredity; it involves the study of cell, individuals, their offspring, and the populations within which the organisms live
Monohybrid cross
constructed by mating individuals from 2 parent strains each of which exhibits one of the 2 contrasting forms of the character under study (Pi=original parents; F1=their offspring)
Dihybrid Cross
Constructed by mating individuals from 2 parent strains when genes under study are on different chromosomes. There are 2 pairs of contrasting forms of character under study; individuals resulting from self-fertilization of the F1 generation are called F2
Mendel’s 1st Postulates
- Unit factors in pairs- genetic characters are controlled by unit factors that exist in pains in indiv. organisms