EMES 204 Ch. 2

cell envelope

consists of a series of layered structures that surround the cytoplasm and govern cellular interactions with the external environment

simple transport

consists only of a transmembrane transport protein

sodium-proton antiporter

Exchanges sodium ions for protons across membrane.

lac permease

membrane protein that transports lactose into the cell

ABC transporter

binding proteins are involved and energy comes from ATP

- binding protein + transported substance

- ATP-hydrolyzing protein

break part of ATP to make

- ADP → provides spring of energy

group translocation

chemical modification of the transported substance driven by phosphoenolpyruvate

membrane functions

1. permeability barrier

2. anchor proteins

3. energy conservation

peptidoglycan

A protein-carbohydrate compound that makes the cell walls of bacteria rigid

teichoic acids

Polymers found in Gram-positive bacterial cell walls.

Lipopolysaccharide (LPS)

Molecule that makes up the outer layer of the outer membrane of Gram-negative bacteria

Gram-positive bacteria

Bacteria that have a thick peptido glycan cell wall, and no outer membrane. They stain very darkly (purple) in Gram stain.

gram-negative bacteria

Bacteria that have complex cell walls with less peptidoglycan but with lipopolysaccharides. Very toxic and hard to treat.

periplasm

The gel-like material that fills the region between the cytoplasmic membrane and the outer membrane of Gram-negative bacteria.

s-layer

an outermost cell surface layer composed of protein or glycoprotein present on some Bacteria and Archaea

major elements

Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), Phosphorus (P), Sulfur (S)

micronutrients

Iron (Fe), Magnesium (Mg), and others

trace elements

Cobalt, Lanthanum, and other rare earth metals

hydrophilic

Attracted to water (phosphate head)

hydrophobic

Water fearing (fatty acid tail)

phospholipid

consists of polar phosphate head and nonpolar lipid tail; make up the phospholipid bilayer in the cell membrane

selective permeability

A property of a plasma membrane that allows some substances to cross more easily than others.

transmembrane proteins

integral proteins that do not extend all the way through the membrane.

peripheral proteins

The proteins of a membrane that are not embedded in the lipid bilayer; they are appendages loosely bound to the surface of the membrane.

Why do polar molecules have difficulty passing through the phospholipid bilayer?

Two factors contribute. First, the negatively charged phosphate head groups can repel other charged molecules. Second, the hydrophobic interior of the bilayer is chemically incompatible with polar or charged molecules, creating a strong energetic barrier to their passage.

What structural properties allow the cell wall to provide strength while still permitting molecular exchange?

The cell wall, composed of peptidoglycan, provides mechanical reinforcement to counteract the approximately 2 atmospheres of internal osmotic pressure while maintaining porosity for molecular exchange

How is the cell membrane analogous to a battery in terms of energy conservation?

Functions as a biological battery by maintaining a proton gradient (high H⁺ outside, low H⁺ inside), which drives ATP synthesis and other energy-requiring processes

What is changing shape during ABC transport — the substrate or the proteins?

The proteins change shape, not the substrate. Specifically, ATP hydrolysis causes a conformational change in the ATPase component, which in turn causes the transmembrane protein to open and facilitate substrate passage. The substrate itself remains chemically unchanged in ABC transport (unlike group translocation).

What prevents the substrate-binding protein from simply drifting away into the environment?

the periplasm