PROKARYOTIC CELL Flashcards
WHAT IS THIS CELL?
-prokaryotic cell
WHAT TYPE OF CELLS DO ANTIBIOTICS TREAT?
-prokaryotic
WHAT IS THE NUCLEOID?
-region with genetic material in the cytoplasm
-contains 1 molecule of usually circular double stranded DNA connected to plasmatic membrane (OriC replication region)
-1000 - 4000 protein coding genes
-Histone Like Proteins which wrap DNA into loops
IS THE PROKARYOTIC CELL HAPLOID OR DIPLOID?
-prokaryotic cell is haploid – does not contain chromosome pairs, only one specific chromosome in a cell to which to which there are no copies
ARE THERE INTRONS IN PROKARYOTES?
-no, only in Archaea in tRNA and mRNA
WHAT DOES THE PROKARYOTIC GENOME CONSIST OF?
-a high density of structural genes
WHAT IS A PLASMID?
- small circular double stranded DNA
-can be several in a cell, not vital for life
-contain genes that can have an evolutionary advantage = reproduce independently from the main chromosome
F PLASMIDS: genes indispensable for conjugation
R PLASMIDS: genes producing resistance to antibiotics
Col PLASMIDS: genes whose products are able to kill other bacteria
DEGRADATIVE PLASMIDS: break down abnormal substances
WHAT IS THE DIFFERENCE BETWEEN A PROKARYOTIC AND A EUKARYOTIC CYTOPLASM?
-a eukaryotic cytoplasm has a cytoskeleton but a prokaryotic cytoplasm does not have a cytoskeleton
WHAT IS IN THE CYTOPLASM?
-in the cytoplasm DNA replication, transcription and translation of mRNA is carried
-translation and transcription occur at same time as DNA is not hidden under nuclear envelope and no introns present
-Ribosome 70S present here
= large complexes made from proteins and rRNA
= 3 types of rRNA - 5S, 16S a 23S
= have proteosynthetic activity (make proteins)
= unit 70S is the rate of sedimentation (eukaryotic ribosomes have 80S)
WHAT IS THE PLASMATIC MEMBRANE?
-it is a selective barrier against the external environment
-made of a phospholipid bi-layer
HYDROPHILIC = head
HYDROPHOBIC = tail
WHAT IS THE CELL WALL MADE OF?
-peptidoglycan polymers which makes it strong and rigid
-on a sugar base there is a bounded protein (murein)
WHAT IS A GRAM POSITIVE CELL WALL?
-stains purple
-thick cell wall from peptidoglycan
-lipoteichoic and teichoic acids
WHAT IS A GRAM NEGATIVE CELL WALL?
-stains pink
-thin cell wall from peptidoglycan
-outer membrane of lipopolysaccharides
-lipid A and O polysaccharide
WHAT IS THE ROLE OF FLAGELLUM?
-movement
-simpler than eukaryotic - thinner and non membrane
-formed by flagellin
WHAT ARE THE SHAPES OF PROKARYOTIC CELLS?
-cocci, bacilli, spirochete
HOW MUCH SMALLER IS A PROKARYOTIC CELL TO A EUKARYOTIC CELL?
-prokaryotic cell size is usually 1-10μm
roughly 10x smaller in diameter and has a 1000x smaller volume
WHAT ARE EPISOMES?
-extrachromosomal genetic element (e.g. plasmid), whose presence can give a selective advantage
-the replication of episomes are autonomous, can occur in the cytoplasm of the bacteria or the episome can become integrated into a chromosome and replicate with it
-episomes can be plasmids, transposons (free DNA with the ability to change location on a chromosome) , insertion sequences or bacteriophage integrated into chromosome
WHAT ARE THE MAIN CHARACTERISTICS OF BACTERIA?
-DNA is not organised into nucleosomes
-genes are without introns
-cell wall is made from peptidoglycans
-FA joined to glycerol by ester bonds
-simple RNA polymerase (4polypeptides)
-thymine is present in tRNA
-binary fission
WHAT ARE THE MAIN CHARACTERISTICS OF ARCHAEA?
-extreme conditions
-cell wall is made from pseudopeptidoglycans
-DNA organised into similiar structures as nucleosomes
-plasma membrane has branched phlantyl sidechains instead of straight fatty acids
-genes from tRNA and mRNA contain introns
-FA joined to glycerol by ether bonds
-complex RNA polymerase (+8polypeptides)
-thymine is absent in tRNA
-no evidence that they cause disease
-important for gut, mouth, skin microbiota
-use more sources of energy = ammonia, metal ions, hydrogen gas
-actin cytoskeleton
-binary fission, fragmentation, budding
WHAT IS THE CYTOSOL?
-liquid-gel part of the cytoplasm
-composed of water, salts, other dissolved solutes
-ribosomes and cytoskeleton here
-most chemical reactions occur here
GIVE AN EXAMPLE OF A SPECIALIZED PROKARYOTIC ORGAN FROM MEMBRANE INVAGINATION.
-infoldings of plasma membrane function in cellular respiration in some aerobic prokaryotes (resemble cristae)
HOW DO PROKARYOTIC CELLS ALTER THEIR GENOME?
-direct transfer of DNA through horizontal gene transfer
HOW DOES HORIZONTAL GENE TRANSFER OCCUR?
-occurs through parasexual processes = mainly transformation, conjugation and transduction
WHAT IS BACTERIAL TRANSFORMATION AND EXPLAIN ITS PROCESSES.
-the uptake of free DNA molecules by competent protein cells (RESTRICTION ENDONUCLEASES = cut DNA so that it can bind to a new location)
1:binding of double stranded DNA fragment to transmembrane receptors, travel via active transport, DNA separates into 2 strands due to degradation of hydrogen bonds via endonucleases
2:DNA is transported into recipients chromosome, G+ can receive one stranded DNA, G- can receive double stranded DNA
3:recombination of DNA between donor and recipient results in a heteroduplex (one original chain one transformed chain)
GRIFFITH (1928) = live non-infected bacteria via transformation received DNA from dead infected bacteria and managed to then kill the mouse
-repeated by Avery, McLeod, McCarthy (1944) with isolated DNA
GIVE EXAMPLES OF PATHOGENIC BACTERIA.
ANTHRAX = bacillus anthracis
WHOOPING COUGH = bordetella pertussis
LYME DISEASE = borrelia burgdorferi (ticks)
BOTULISM = clostridium botulinum
TETANUS = clostridium tetani
DIPHTERIA = corynebacterium diphteriae
PEPTIC ULCER = helicobacter pylori
LEPROSY = mycobacterium leprae
TB = mycobacterium tuberculosis
GONNORHEA = neisseria gonorrhoeae
TYPHOID FEVER = salmonella typhi
PNEUMONIA = streptococcus pneumoniae
SCARLET FEVER = streptococcus pyagenes
SYPHILIS = treponema pallidum
CHOLERA = vibrio cholerae
BLACK DEATH = yersinia pestis
WHAT ARE THE DIFFERENCES BETWEEN PROKARYOTIC AND EUKARYOTIC CELLS?
PROKARYOTC
-1 - 10μm
-1000 - 4000 genes
-without organelles and cytoskeleton
-non-miotic division of chromosomes
-irregular nucleus
-transcription and translation occur at same time and same place
-70S ribosomes (30s, 50s subunit) (5,16,23S)
EUKARYOTIC
-5 - 100μm
-10,000 - 30,000 genes
-enclosed organelles and cytoskeleton
-miotic division of chromosomes
-regular nucleus
-nuclear membrane separates processes: transcription occurs in the nucleus and translation occurs in the cytoplasm
-80S ribosomes
WHAT IS THE BACTERIAL COLONY GROWTH CURVE?
-Number of live cells in a bacterial population over a period of time
Lag phase - bacteriaadapt to growth conditions. They are not dividing.
Log phase(also called logarithmic phase or exponential phase)
bacterial cell number doubling.
Stationary phase - growth reaches a plateau as the number of dying cells equals the number of dividing cells.
Death phase - an exponential decrease in the number of living cell.
WHAT DO PLASMIDS ENCODE GENES FOR?
-resistance to antibiotics or heavy metals
-metabolic enzymes involved in nitrogen fixation
HOW DOES A PLASMID REPRODUCE?
-independently once they have an origin of replication (Ori)
WHAT IS BACTERIAL CONJUGATION AND DESCRIBE ITS PROCESSES.
-transfer of DNA using a conjugation bridge coded by an F plasmid or by direct contact
-bacteria with an F plasmid is F+ and bacteria without it is F-
-F+ cell comes into contact with F- cell via pilus and a strand of plasmid DNA is transferred. Recipient synthesizes a complementary strand to become F+ and the F+ strand makes another copy to restore itself
-transferred DNA is often beneficial to the recipient
WHAT IS THE Hfr BACTERIA?
If F plasmid is not free in the cytoplasm but integrated into a
chromosome, the cell is called a Hfr cell (High frequency of recombination cell)
-during conjugation with a Hfr cell, the recipient cell receives an F plasmid integrated within a chromosome. If the full F plasmid is not transported successfully, the following cell will be a recombinant and will remain a F- cell, because a F+ cell requires a full F plasmid
WHAT IS TRANSDUCTION AND EXPLAIN ITS PROCESSES.
-transfer of DNA via bacteriophage
WHAT IS THE MECHANISM OF ROLLING CIRLCE REPLICATION / UNIDRIECTION CONJUGATION?
a) An endonuclease cut one DNA strand.
b) A new DNA strand is formed in direction 5´→3 and transmitted to the recipient cell.
c) A new strand is formed made up of Okazaki fragments.
WHAT IS GENERAL TRANSDUCTION?
GENERAL / NON SPECIFIC: transfer of any part of host DNA (bacterial genes) - occurs during lysis
1. Bacterial cell is Infected by phage DNA
2. Fragmentation of bacterial chromosome
3. DNA (viral and bacterial) is packaged in a protein coat/capsid => sometimes a bacteriophage can be accidently formed, which carriers only bacterial DNA; cell lysis occurs
4. Bacteriophage carrying pure bacterial DNA can infect others (acceptors)
5. bacterial DNA from donor bacteria transported by a bacteriophage is integrated into the chromosome of acceptor cell
WHAT IS SPECIFIC TRANSDUCTION?
SPECIALIZED / SPECIFIC: transfer of a particular part of the host DNA with viral genes
-due to an incorrect excise of bacteriophages genome from bacterial chromosome during a transition from lysogenic to lytic cycle
- bacteriophage DNA is incorporated into bacterial chromosome NOT accidently – requires specific insertion sequences
- during excision of phage DNA, a mistake occurs and alongside phage DNA a part of bacterial DNA is taken with it
- bacteriophage which carriers both DNAs, infects other bacteria and donates its own and bacterial DNA to the acceptor cell
- due to the non-accidental integration, specific transduction is used in genetic engineering
GENE EXPRESSION IN PROKARYOTES OCCURS AT WHICH LEVEL?
-transcriptional
WHAT GENES ARE ALWAYS EXPRESSED IN PROKARYOTES?
house keeping genes / constitutive genes
WHAT ARE INDUCIBLE GENES?
-genes for catabolic enzymes, which become expressed in the presence of a reaction substrate
WHAT ARE REPRESSIBLE GENES?
-genes for enzymes of anabolic reactions, stop being expressed during the presence of a reaction product (negative feedback)
WHAT IS AN OPERON?
-functional unit of transcription and gene regulation for prokaryotes
-it is a cluster of genes transcribed into one mRNA (polycistronic transcript) (promotor, operator, structural)
-many genes can be transcribed at the same time – hence polycistronic -> in eukaryotic cells only one gene can be transcribed into a molecule of RNA
WHAT IS A PROMOTER?
-a nucleotide sequence that enables a gene to be transcribed. The promoter is recognized by RNA polymerase, which then initiates transcription.
WHAT IS AN OPERATOR?
-a segment ofDNA to which a repressorbinds. The repressor protein obstructs the RNA polymerase from transcribing the genes.
WHAT ARE STRUCTURAL GENES?
-genes coding enzymes for a given metabolic pathways
WHAT ARE REGULATORY GENES?
- product is an activator (in positive operons) or repressor (in negative operons) = allosteric proteins
- effectors bind onto activators or repressors and cause an allosteric change which changes their function
( inductors (take part in induction - transcription occurs) or corepressors (take part in repression – transcription does not occur))
WHAT IS THE LAC A TRP OPERON?
-the Trp operon (co-repressor) is required for the production of tryptophan in Escherichia coli
-5 genes: Antranilate synthase
Phosphoribosylantranilate isomerase
Indole-3-glycerol-phosphate synthase
Tryptophan synthase subunits (x 2)
+SERINE
-if tryptophan is already present, the structural genes are not transcribed
-regulated by attenuation (a mechanism based on coupling of transcription and translation)
-genes of the Trp operon are transcribed as a single mRNA
-anabolic pathway and negative regulation
WHAT IS THE LAC OPERON?
-required for the transport of lactose in Escherichia coli, allows bacteria to digest lactose when glucose is not available (HIGH LACTOSE, LOW GLUCOSE)
-LAC REPRESSOR = lactose sensor (blocks RNAP)
-when lactose levels are high allolactose removes repressor and transcription can occur
-CATABOLITE ACTIVATOR PROTEIN = glucose sensor (promotes binding of RNAP to the operator) (cAMP forms when glucose levels are low and helps CAP bind DNA)
-three genes: lacZ (B-galactosidase), lacY (B-gal permease), and lacA (B-gal transacetylase). These genes are transcribed as a single mRNA, under control of one promoter.
-negative (lactose absent) and positive regulation (glucose absent)
WHICH PROKARYOTE DOES NOT HAVE A CELL WALL?
mycoplasma lack a cell wall
WHY ARE ARCHAEA CONSIDERED MORE CLOSELY RELATED TO HUMANS THAN BACTERIA?
due to the presence of introns
DO ALL PROKARYOTES HAVE CELL WALLS?
no
