Microbial Metabolism, Structure, and Function Flashcards Preview

Microbiology Exam 1 > Microbial Metabolism, Structure, and Function > Flashcards

Flashcards in Microbial Metabolism, Structure, and Function Deck (41):
1

What kind of DNA do bacteria have?

One circular chromosome, composed of double-stranded DNA, located in the Nucleoid

2

When are bacteria most susceptible to antimicrobials?

During the Lag Phase and the Exponential Phase

3

When are bacteria less susceptible to antimicrobials?

Stationary phase

4

What phase does sporulation occur in?

Stationary phase

5

What phase is the bacteria actively metabolizing?

Exponential phase

6

What are the minimum requirements for growth?

A source of carbon and nitrogen, an energy source, water, and various ions

7

What four factors determine growth in culture?

pH optimum
Aerobic vs anaerobic
Nutrients/composition of media
Temperature

8

How is cell density determined?

Colony counts on agar plates or by turbidity using spectophotometry

9

Aerobic Bacteria

-Exclusively use respiration to meet energy needs
-E.g. M. tuberculosis, P. aeroginosa, B. anthrasis

10

Anaerobic Bacteria

-Exclusively use fermentation to meet energy needs
-E.g. C. botulinum, Bacteriodes
***Much LESS efficient than respiration
-Will be KILLED BY OXYGEN

11

Facultative anaerobes

Can respire or ferment
E.g. E. Coli, Shigella dysenteriae, S. aureus

12

Microaerophilic

Grow best at low oxygen but can grow without it as well
E.g. C. jejuni

13

How do bacteria counteract the highly reactive forms of oxygen (e.g. Hydrogen Peroxide H2O2 and Superoxide Anion O2-)?

-Catalase (catalyzes the breakdown of H2O2 to H2O and O2)
-SOD (Superoxide Dismutase; expressed by both prokaryotes and eukarotes to detoxify O2-)

14

Bacteria that lack SOD and Catalase are...

Sensitive to oxygen and likely Anaerobic

15

Fermentation

Pyruvate is converted to various end products, which then can be used to identify bacteria in the lab

16

5 targets of antibiotics

1. Cell wall synthesis
2. DNA replication
3. RNA synthesis
4. Protein synthesis
5. Antimetabolites

17

Nucleic Acid Biosynthesis: Nucleotide Uses

Building blocks of DNA and RNA, ATP and GTP, cofactors (NAD, FAD, coenzyme A), biosynthetic intermediates (UDP-glucose), and second messengers (cAMP, cGMP)

18

Folate is essential in the synthesis of...

Purines and Thymidine

19

Why is folic acid a good target for bacterial toxicity?

Bacteria derive their folic acid from para-aminobenzoic acid (PABA), while mamalian cells use pre-formed folate from the diet

20

What enzyme do Sulfonamides act on?

Dihydropteroate synthase (DHPS); NOT present in mammals

21

What enzyme does Trimethoprim act on?

Dihydrofolate reductase (DHFR); present in mammals, but DIFFERENT

22

Binary Fission: what unwinds bacterial DNA?

Bacterial DNA gyrase

23

What targets bacterial DNA gyrase?

Quinolones

24

What is different about transcription/translation in bacteria?

They are coupled (Co-Transcriptional Translation) as they do not have a nucleus
-70s ribosomes (vs. 80s in eukoaryotes) binds free 5' end of mRNA as DNA is transcribed
-Multiple ribosomes are bound to mRNA forming a polyribosome

25

Structure of Peptidoglycan in E. coli

Bond DAP of the peptide in one chain to the Ala at position FOUR of an adjacent chain

26

General structure of a Peptidoglycan

Peptides are cross-linked through a peptide bond between the terminal D-Alanine from one chain and a Lysine (or other diamino acid) from the other chain

27

Other names for N-acetylglucosamine

NAG, GlcNAc, G

28

Other names for N-acetylmuramic acid

NAM, MurNAc, M

29

Step 1 of Cell Wall Biosynthesis

Activation of carbohydrate subunits with UDP

30

Step 2 of Cell Wall Biosynthesis

A pentapeptide is added to UDP-NAM

***Important: this step is INDEPENDENT of mRNA and ribosomes; it is produced ENZYMATICALLY

31

What is the order of the amino acids coming off NAM-UDP?

L-ala (variable)--- D-glu (variable) --- L-lys (diamino acid; Lysine, diaminopilemic acid) --- D-ala --- D-ala

***The D-ala's do not change; they are important in cross-linking

32

Step 3 of Cell Wall Biosynthesis

UDP-NAM-pentapeptide is attached to the BACTOPRENOL through a pyrophosphate link with the release of UMP

33

What is Bactoprenol?

Lipid carrier found in the cytoplasmic membrane

34

Step 4 of Cell Wall Biosynthesis

NAG is added to NAM-pentapeptide-bactoprenol complex

35

Step 5 of Cell Wall Biosynthesis

The bactoprenol carrier transports the completed NAG-NAM pentapeptide repeat unit across the membrane

36

Step 6 of Cell Wall Biosynthesis

The disaccharide unit is attached to the end of the growing peptidoglycan chain by enzymes called TRANSGLYCOSYLASES

37

Step 7 of Cell Wall Biosynthesis

Pyrophosphobactoprenol is converted to phosphobactoprenol and recycled

38

What is the mechanism of Vancomycin?

Prevents Penapeptide-NAM-NAG from attaching to Peptidoglycan

39

What is the mechanism of Bacitracin?

Prevents Bactoprenol from crossing the membrane

40

Peptidoglycan synthesis - Outer leaflet of cell membrane: Transpeptidation

Occurs between the free amine of the diamino acid in the 3rd position of the pentapeptide (or the N-terminus of the attached pentaglycine chain) and the D-alanine at the 4th position of the other peptide chain, RELEASING THE D-ALANINE PRECURSOS

41

Transpeptidases

Mediate transpeptidation reaction
-Also called Penicillin Binding Proteins (PBP) because they are targets for penicillins and other B-lactam antibiotics