bio class 9

What are the general characteristics and functions of lipids in bacteria?

Lipids are a heterogeneous group of hydrophobic molecules soluble in organic solvents like methanol and chloroform. Most bacterial lipids are in membranes as phospholipids. Functions include forming membrane bilayers, storing energy, assisting in protein folding, enabling signaling, and acting as cofactors in electron transport (e.g., ubiquinone).

What are the structural features of fatty acids?

Fatty acids consist of a carboxyl group attached to a hydrocarbon chain, usually unbranched and containing an even number (4-28) of carbons. They are amphiphilic, with hydrophobic hydrocarbon tails and hydrophilic heads. Unsaturated or branched chains increase membrane fluidity.

How do fatty acids occur in bacteria?

Fatty acids are not free molecules; they are esterified to other compounds such as glycerol (forming phosphoglycerides), glucosamine (forming Lipid A in LPS), or proteins (forming lipoproteins).

What is the function of the acetyl

CoA carboxylase complex?- It catalyzes the first step of fatty acid synthesis, converting acetyl-CoA to malonyl-CoA using CO₂ and biotin as a cofactor. The complex has three components: biotin carboxyl carrier protein (BCCP), biotin carboxylase, and carboxyltransferase.

What is the role of the acyl carrier protein (ACP)?

ACP holds the growing acyl chain and carries intermediates between enzymatic sites during synthesis within the fatty acid synthase complex.

What are the four main reactions in the fatty acid elongation cycle?

1. Condensation (ketoacyl-ACP synthase) 2. 1st reduction (ketoacyl-ACP reductase; uses NADPH) 3. Dehydration (hydroxyacyl-ACP dehydratase) 4. 2nd reduction (enoyl-ACP reductase; uses NADPH) Each cycle adds two carbons until a 16C fatty acid (palmitate) forms.

How are unsaturated fatty acids formed in bacteria?

Via FabA (a dehydratase/isomerase) acting on C-10 intermediates or by desaturase enzymes introducing double bonds into existing fatty acids.

What compound inhibits enoyl

ACP reductase?- Triclosan, an antimicrobial agent that blocks the final reduction step in fatty acid synthesis.

What are phospholipids and how are they synthesized in E. coli?

Phospholipids are amphipathic molecules forming the cell membrane. In E. coli: Glycerol-3-phosphate is acylated to form phosphatidic acid, then converted via the Kennedy pathway into phosphatidylethanolamine (PE), phosphatidylglycerol (PG), or cardiolipin (CL).

What are the relative proportions of phospholipids in E. coli membranes?

~70% PE, 25% PG, and 5% CL.

Why are unsaturated and branched

chain fatty acids important in bacteria?- They increase membrane fluidity, which maintains function under environmental stress.

What are short

chain fatty acids (SCFAs) and their biological benefits?- SCFAs (acetate, propionate, butyrate) acidify the colon, inhibit pathogens, aid mineral absorption, and improve gut health.

What is the significance of liposomes in biology and medicine?

Liposomes are lipid bilayer vesicles used to model membranes and deliver drugs or vaccines (e.g., mRNA COVID-19 vaccines).

How does the Fluid Mosaic Model describe membrane structure?

Proposed by Singer and Nicolson (1972), it depicts a fluid phospholipid bilayer with embedded proteins; hydrophobic amino acids interact with lipids and hydrophilic with water.