Lecture 5 Flashcards
In prokaryotes where does DNA replication, transcription and translation occur?
cytoplasm
Most prokaryotes have how many chromosomes and what shape?
single circular chromosome
Why do prokaryotes have a circular chromosome?
protection from exonuclease which chew up naked linear DNA
If a bacteria has linear chromosomes how can it protect itself?
hairpins or covalently bound proteins protect it from exonucleases
how is DNA packed in prokaryotes?
supercoiled loops around a central core, looks like a bottlebrush
How does DNA alleviate torsion?
right-handed supercoils = negatively supercoiled
What two enzymes regulate supercoiling?
gyrase and topoisomerase 1
What does gyrase do?
cuts DNA and introduces negative supercoils
What does topoisomerase 1 do?
creates positive supercoils (left handed supercoiling) by making single strand breaks that relax supercoils
What state is the DNA usually in? why?
slightly negatively supercoiled, causes slight strand separation
where does transcription occur in prokaryotes? where doesn’t it occur and why?
nucleoid/cytoplasm interface, doesn’t occur in middle of nucleoid bc enzymes can’t get there and DNA can’t relax
Is transcription and translation coupled in prokaryotes?
yes
Is the cytoplasm crowded? what is the benefit?
yes, helps in protein folding and in coupling cellular processes
What is the purpose of gas vesicles?
increase a cells buoyancy which helps aquatic prokaryotes receive the most light
What is the structure of gas vesicles?
protein shell that is permeable to gases and repels water
—-no lipid membrane that would hinder gas diffusion
What is the purpose of thylakoids?
increase SA membranes that house the photosynthetic machinery. contain necessary pigments, proteins, and cofactors needed to capture light energy
Do cyanobacteria have thylakoids?
yes
What is the purpose of carboxysomes? structure?
confines the special enzymes needed for carbon fixation
made of a proteins shell
Where are carboxysomes found?
autotrophic bacteria that fix CO2
Where are enterosomes found?
heterotrophic bacteria, found in the gut
What is the purpose of enterosomes?
contain enzymes that metabolize propanediol and ethanolamine.
help bacteria cope with toxic propanaldehyde
What is fucose?
metabolie of propendiol and is a common sugar in the mammalian intestine
What is polyhydroxyalkanoate (PHA)?
carbon polymers that can be used when carbon becomes limiting —can be stored in a storage granule
What are magnetosomes composed of?
membrane-bound iron containing crystals
What is the purpose of magnetosome?
allow bacteria to align themselves with the earth’s magnetic field and provides them with a sense of direction
–can swim towards lower o2 concentrations which they prefer
