[魯國共筆目錄](/f422AdmtSGeEnkS-LwYuqA?fbclid=IwAR2EKSabdgiJ_5kq0K06l6Q9k_zUuqT-L_kI0zr-J3VN3cf3b50M7hD8Ly0)
# Bacteria Introduction
###### tags: `共筆`
## The structure of bacteria

### 1. Cytoplasm
* DNA chormosome
* Plasmids
* 常於革蘭氏陰性菌`Gram(-)`找到
* 並非細菌生存必須
* <font color = "red">provide a selective advantage</font>
* mRNA
* <font color = "red">transcription and translation are coupled</font>
* Ribosome
* 30s + 50s -> 70s

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### 2. Cytoplasmatic membrane
* lipid bilayer
* ==no steroids==
> <font color = "red">mycoplasmas</font> are exception
* Involves electron transport and energy production

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### 3. Cell wall
* Gram(+)
* Peptidoglycan (胜肽聚醣)
> <font color = "blue">Lysozyme</font> can degrade peptidoglycan
> <font color = "red">Protoplast</font> (原生質體): 缺乏細胞壁（peptidoglycan）的**陽性菌**
* <font color = "red">Teichoic acid</font> (胞壁酸)
* <font color ="blue">Covalently linked</font> to the pepdioglycan
* important factor in <font color = "red">virulence</font>(毒性)
* <font color = "red">Lipoteichoic acid</font> (脂胞壁酸)
* anchored in the cytoplasmatic membrane
* initiate endotoxic-like activities(毒性較弱)
> Teichoic acid and Lipoteichoic acid
>> are common surface Ag -> **bacterial serotype**
>> can promote attachment (**adherence**)
>>
![Gram(+) cell wall](https://i.imgur.com/2PTJFN9.png "Gram(+) cell wall" =400x)
* Gram(-)
* **Thin** peptidoglycan layer
> no techoic acid or lipotechoic acid
* Periplasmic space
> contain transport system, metabolites and hydrolytic enzymes
> many are <font color = "blue">lytic (溶血的) virulence factors</font>
* <font color = "red">Porin protein</font> (膜孔蛋白)
> allow the diffusion of **hydrophilic** molecules
* Outer membrane: ==asymmetric bilayer==
* inner leaflet: phospholipid
* outer leaflet: <font color = "red">Lipopolysaccharide (LPS)</font> `endotoxin`
> attached to the peptidoglycan by **lipoprotein links**
> held together by **divalent cation** (陽離子)(Mg^2+^, Ca^2+^)
>> can be disrupted by antibiotics or EDTA
>> <font color = "red">pheroplasts</font> (球形質體): 缺乏細胞壁（peptidoglycan）的**陰性菌**
>>
![Gram(-) cell wall](https://i.imgur.com/E4UwfFS.png "Gram(-) cell wall" =350x)
* Biosythesis
* Peptidoglycan synthesis:
Disaccharides -> polysaccharide -> polysaccharide chains -> Peptidoglycan
* Disaccharides:
N-acetylglucosamine (==GlcNAc==, NAG, G) &
N-acetylmuramic acid (==MurNAc==, NAM, M)
* polysaccharide chains -> Peptidoglycan
cross-linking reaction: transpeptidation
> <font color="red">Transpeptidase/penicillin binding proteins(PBP)</font> can inhibit cross-linking
> => antibiotics
>
* Gram(+) peptidoglycan component
A <font color="red">pentaglycine bridge (gly5)</font> expands the cross-link
* Gram(-) peptidoglycan component
<font color="red">Diaminopimelic acid</font> is directly linked to the terminal alanine of another chain
* Overview
![Peptidoglycan synthesis](https://i.imgur.com/Xa8aUyD.png "Peptidoglycan synthesis" =500x)
* Teichoic acid synthesis
> connect by **phosphate**
> The nature of the modification can define the **serotype** of the bacteria.
>
* Lipopolysaccharide synthesis
* one ==Lipid A== (<font color="red">endotoxin activity</font>)
* one ==polysaccharide core== unit
* many repeats of ==O antigen==
![Lipopolysaccharide](https://i.imgur.com/N0f0MIj.png "Lipopolysaccharide" =250x)
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### 4. External Structures
* Capsule (夾膜): bacteria are closely surrounded by ==loose polysaccharide or protein layers==
* Slime layer (黏液層): loosely adherent and non-uniform in density and thickness
* <font color="red">glycocalyx(醣膠層)</font>
> Exception: <font color="red">B.anthracis (炭疽桿菌)</font>: produce ==polypeptide== capsule
> =>十分堅硬，染劑無法染進去
* unnecessary for the growth of bacteria but are important for <font color="red">survival in the host</font>
> 有時在培養盤上養的細菌就無莢膜，因為沒有生長壓力
* <font color="red">poorly antigenic, antiphagocytic, a major virulence factor, promote adhesion</font>
> =>幫助細菌於宿主體內生長
* Biofilm (菌膜)
* polysaccharide
* protect bacterial <font color="red">from antibiotics and host defenses</font>
* ex: Pseudomonus aeruginosa; 綠膿桿菌
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### 5. Flagella(鞭毛)
* Ropelike propellers
* Provide motility for bacteria
* allowing the cell to swim(==chemotaxis==)
* Four types of arrangement
* Monotrichous (一端有單鞭毛)
* Amphitrichous (二端有鞭毛)
* Lophotrichous (一端有束鞭毛)
* Peritrichous (周身有鞭毛)
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### 6. Fimbriae (纖毛)(pili;線毛)
* Promote ==adherence== to other bacterial or to the host
> 像是魔鬼氈
> for colonization and infection
> adhesin (黏附素); lectin (凝集素); evasins (逃避素); aggressin (攻擊素)
* F pili (<font color="red">sex pili</font>)
* promote the ==transfer of large segments of bacterial chromosomes== between bacteria
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### 7. Spores (芽胞)
* 僅存在<font color="red">Gram(+)</font> ex: ==Bacillus==(桿菌類), ==Clostridium==(梭狀菌屬)
* 對抗惡劣環境，從生長狀態(vegetative state)變成冬眠狀態(dormant state)
* 高濃度的==dipicolinic acid==與==calcium==結合，產生很硬的結構