Flashcards in 1-3 Bacterial Structure Deck (25)
What are some of the main characteristics of the bacterial genome?
DNA clumps in a nucleoid
Single circular chromosome
What size are bacterial ribosomes?
How do bacteria reproduce?
All of the following are correct except for?
A. Bacteria have a peptidoglycan cell wall
B. Eukaryotic cells have 80S ribosomes
C. Both bacteria and eukaryotes have a membrane bound nucleus
D. Bacteria lacks introns
C. Both bacteria and eukaryotes have a membrane bound nucleus
Eukaryotes have a membrane bound nuclues, while bacteria have a nucleoid region that is not membrane bound.
What are the four major shape types of bacteria?
What are examples of each?
1. Cocci (round) ex. staph, strep
2. Rods (oval) ex. E. coli, pseudomonas
3. Vibrios (curved rods) ex. cholera
4. Spirochetes (corkscrew) ex. borrelia (lyme), treponema (syphilis)
Describe the gram staining procedure (5 steps)
1. Fix bacteria to microscope slide with heat
2. Stain with crystal violet (all bacteria turn purple)
3. Iodine treatment (Gram+ become permanently purple)
4. Decolorize with alcohol (Gram- lose purple stain)
5. Counterstain (safrinin re-stains Gram-)
What aspect(s) of the bacterial cell wall is/are different between Gram+/- bacteria?
Gram + bacteria have 3x thicker layer of peptidoglycan and no exterior membrane
Gram- bacteria have thinner layer of peptidoglycan and contains an exterior membrane
What is the third category of cell wall type and how do they stain?
Mycolic (mycobacteria), also known as acid-fast.
They do not stain Gram + but are structurally different from Gram -, need to perform acid fast procedure
Is Gram staining a definitive way to make a diagnosis clinically?
No, Gram staining seldom makes the diagnosis but it does narrow down the differential and is fast and cheap....it is the MOST commonly ordered lab test.
Can occasionally make the diagnosis...Gram- diplococci in cervical smear=gonorrhea
What is LPS?
Component of Gram- cell walls
It is an endotoxin that can cause septic shock either during sepsis or following antibiotic treatment when the bacteria dies and releases LPS into the bloodstream.
What are the two versions of glycocalyx and what are their functions?
1. Slime layer: loose coating of polysaccharide that helps bacteria attach to host cells, forms biofilms.
2. Capsule: firm enclosure that helps with attachment, resists phagocytosis, often a virulence factor
What are biofilms?
Biofilms are diverse microbial communities that may host fastidious organisms, more resistant than pure colonies to both hygienic measures and antibiotics.
What is the function of Pili/fimbrae and how to Gram+/- differ?
Used for attachment, often a virulence factor
Gram+ pili are simple and newly discovered
Gram- pili are complex and include Type 1 attachment and variants Type 4 propulsion, Types 3&4 secretion
Cite the unique structural properties of bacteria that differentiate them from viruses and eukaryotes.
bacteria have PM, at least one peptidoglycan cell layer, some gram - have a glycocalyx. Much larger tahn viruses
bacteria and eukaryotic cells have more in common but still very different. Bacteria lack nuclei (any any other membrane bound organelles), have 70s ribosomes as opposed to 80s in eukaryottes. bacteria cells are also smaller
Explain the pathogenic significance of the relative size of bacteria compared to animal cells.
hundreds can fit inside eukaryotic cell, leads to intracellular means of pathogenicity. also allows for bacteria to phagocytized during immune response.
4 common appearances of bacteria under light microscopy
Cocci – Round shape (Staph, Strep).
Rods – Oval shape (E. coli, Pseudomonas).
Vibrios – Curved rod shape (V. cholerae).
Spirochetes – Corkscrew shape (Borrelia, Treponema).
Name two bacterial structures that have pathogenic significance.
Lipopolysaccharide (LPS) – Component of Gram-negative cell walls. Can cause septic shock when released from dead bacteria into blood.
Glycocalyx – Can be a slime layer (loose polysaccharide coating for attachment that helps the formation of biofilms) or a capsule (firm enclosure that is mainly for immune evasion, but also helps with attachment).
Discuss, in general terms, the importance of biofilms in environmental microbiology and pathogenesis.
A biofilm is a community of diverse microbes that live in a complex matrix. The microbes produce metabolites for each other, can protect each other from antimicrobials, and do other things. When biofilms are present in a medical setting, it is a big problem.
Memorize the Gram stain procedure and the importance of Gram staining.
1. Fix bacteria to a microscope slide with heat.
2. Stain with crystal violet (turns all bacteria purple).
3. Treat with iodine (Gram-positives will be made to retain the CV).
4. Decolorize with alcohol (leaches purple from Gram-negatives).
5. Counterstain (general with safranin; re-stains Gram-negatives pink).
-fast, cheap, effective way of narrowing down differential. Gram + retain CV due to thicker peptidoglycan wall
Describe the structure of the nuclear pores and the basic mechanisms of transport through the pores.
Proteins and ribonucleoprotein complexes (protein-bound RNA’s) pass through the nuclear pores. Small proteins can pass through freely, but larger proteins need a nuclear localization signal.
Cargo is imported and exported using the small GTPase called Ran and its two associated factors: Ran GTPase Activating Protein (GAP) and a Ran GTP Exchange Factor (GEF). For import, cargo is bound to the protein importin, and then moves through a nuclear pore into the nuclear lumen. Inside the nucleus, Ran GTP binds importin, causing it to release its cargo into the nucleus. Ran GTP brings importin back to the cytosol, hydrolyzing to Ran GDP when it releases the importin. For export, exportin binds cargo and Ran GTP. The complex passes through the nuclear pore into the cytosol. There, Ran GTP is hydrolyzed to Ran GDP and the cargo is released into the cytosol.
Describe the organization of the nucleolus and its role in the ribosome biogenesis.
The nucleolus is a sub-compartment of the nucleus built upon the rDNA repeats of the genome. Its main function is ribosome biogenesis. Transcription of the rDNA repeats produces the 45S rRNA precursor. The fibrillary center is the region containing DNA that is not being actively transcribed. The dense fibrillary component is the region containing rRNA molecules actively being synthesized. The granular component is the region containing maturing ribosomal precursor particles.
Describe the structure of chromosomes and how they are packaged into chromatin.
Euchromatin is the least dense packaging of DNA. DNA that is actively being transcribed is in the euchromatin form. Heterochromatin is a denser packaging of DNA, for DNA not being actively transcribed during interphase. Chromatin is formed by wrapping DNA around an octomer of histones (two of each of H2A, H2B, H3, and H4).
Each chromosome has replication origins, a centromere, which serves to attach the chromosome to mitotic spindles, and telomeres, stabilizing repeating sequences at the end of the chromosomes.
Describe what a gene is, and what’s meant when we say “a gene codes for…”
A gene is a sequence of DNA that codes for RNA. When we say “a gene codes for…” we are describing the RNA (coding or noncoding) or protein produced when the DNA is transcribed and/or translated.
Nuclear architecture and how it changes at mitosis
At mitosis, transcriptional activity ceases, leading to the dissolution of the nucleolus and condensation of the chromosomes. Then, the nuclear lamin proteins are phosphorylated. This causes them to break down, leading to the breakdown of the nucleus as a whole, turning into vesicles. After mitosis, the lamins are dephosphorylated, causing the nuclear matrix and envelope reassemble around the decondensing chromosomes.