1-3 Bacterial Structure

Question 1

What are some of the main characteristics of the bacterial genome?

Answer 1

DNA genome
No introns
DNA clumps in a nucleoid
Single circular chromosome

Question 2

What size are bacterial ribosomes?

Answer 2

70S ribosomes

Question 3

How do bacteria reproduce?

Answer 3

Binary fission

Question 4

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

Answer 4

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.

Question 5

What are the four major shape types of bacteria?

What are examples of each?

Answer 5

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)

Question 6

Describe the gram staining procedure (5 steps)

Answer 6

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-)

Question 7

What aspect(s) of the bacterial cell wall is/are different between Gram+/- bacteria?

Answer 7

Gram + bacteria have 3x thicker layer of peptidoglycan and no exterior membrane

Gram- bacteria have thinner layer of peptidoglycan and contains an exterior membrane

Question 8

What is the third category of cell wall type and how do they stain?

Answer 8

Mycolic (mycobacteria), also known as acid-fast.

They do not stain Gram + but are structurally different from Gram -, need to perform acid fast procedure

Question 9

Is Gram staining a definitive way to make a diagnosis clinically?

Answer 9

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

Question 10

What is LPS?

Answer 10

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.

Question 11

What are the two versions of glycocalyx and what are their functions?

Answer 11

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

Question 12

What are biofilms?

Answer 12

Biofilms are diverse microbial communities that may host fastidious organisms, more resistant than pure colonies to both hygienic measures and antibiotics.

Question 13

What is the function of Pili/fimbrae and how to Gram+/- differ?

Answer 13

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

Question 14

Cite the unique structural properties of bacteria that differentiate them from viruses and eukaryotes.

Answer 14

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

Question 15

Explain the pathogenic significance of the relative size of bacteria compared to animal cells.

Answer 15

hundreds can fit inside eukaryotic cell, leads to intracellular means of pathogenicity. also allows for bacteria to phagocytized during immune response.

Question 16

4 common appearances of bacteria under light microscopy

Answer 16

Cocci – Round shape (Staph, Strep).

Rods – Oval shape (E. coli, Pseudomonas).

Vibrios – Curved rod shape (V. cholerae).

Spirochetes – Corkscrew shape (Borrelia, Treponema).

Question 17

Name two bacterial structures that have pathogenic significance.

Answer 17

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).

Question 18

Discuss, in general terms, the importance of biofilms in environmental microbiology and pathogenesis.

Answer 18

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.

Question 19

Memorize the Gram stain procedure and the importance of Gram staining.

Answer 19

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

Question 20

Describe the structure of the nuclear pores and the basic mechanisms of transport through the pores.

Answer 20

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.

Question 21

Describe the organization of the nucleolus and its role in the ribosome biogenesis.

Answer 21

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.

Question 22

Describe the structure of chromosomes and how they are packaged into chromatin.

Answer 22

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.

Question 23

Describe what a gene is, and what’s meant when we say “a gene codes for…”

Answer 23

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.

Question 24

Nuclear architecture and how it changes at mitosis

Answer 24

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.

Question 25

why does mycobacterium tuberculosis stain blue?

Answer 25

it does not stain blue. it is an acid fast (like all mycobacteria).