MCB3020 Week 2: Cell Structure & Function

LUCA

Last universal common ancestor

Eukaryotic cell

DNA in nucleus, large & complex cells, has membrane-enclosed organelles; cytoplasmic membrane, ribosomes, nucleus, nucleolus, nuclear membrane, cytoplasm, endoplasmic reticulum, golgi, mitochondria, chloroplast

Prokaryotic cell

DNA in nucleoid, small & fast cells, no membrane-enclosed organelles; cytoplasm, nucleoid, ribosomes, plasmid, cytoplasmic membrane, cell wall

Plasmid

In some prokaryotic cells, this organelle is responsible for special properties such as antimicrobial resistance

Virus

Not considered alive or cells, carries genetic information but relies on a host to function

Coccus

Spherical shape of cell

Rod

Cylindrical shape of cell

Spirilla

Spiral shape of cell

Spirochete

Like spirillum but longer

Filamentous bacteria

Like rod but longer

Smallness

Cells benefit from this due to having a higher surface area to volume ratio, allowing greater nutrient exchange, better waste exchange, and greater metabolic rate (faster growth), most cells like this are found in the open ocean

Prochlorococcus marinus

Good representative of a small, photosynthetic, marine microbe

Phospholipid bilayer

General structure for bacteria and eukarya cytoplasmic membranes, amphipathic where the hydrophobic tails are inside and the hydrophilic heads are outside. Made of fatty acids

Isoprene

In archaea, the membrane phospholipids are made of this

Membrane functions

Permeability barrier, protein anchor, energy conservation

Membrane stability

Embedded proteins, hydrogen bonds and hydrophobic interactions, Mg2+ and Ca2+ forming ionic bonds

Integral membrane proteins

In Bacteria, these proteins are firmly embedded in the membrane

Peripheral membrane proteins

In Bacteria, these proteins have one portion anchored in the membrane, such as lipoproteins

Sterols

In Eukaryotic membranes, this helps strengthen the membrane.

Hopanoids

In Bacterial membranes, this helps strengthen the membrane.

Ether

In Archaeal membranes, there are _ linkages in the phospholipids

Ester

In Bacterial and Eukaryotic membranes, there are _ linkages in the phospholipids

Lipid monolayer

Archaea has this type of membrane and doesn’t separate by heat easily

Simple transport

Driven by energy in the proton motive force; a proton travels with the transported substance

Group translocation

Chemical modification of the transported substance driven by phosphoenolpyruvate (PEP); chemical modification of the transported substance gains a phosphate thru phosphorylation

ABC system

Periplasmic binding proteins are involved, and energy comes from ATP; a periplasmic binding protein binds to the transported substance and ATP is turned back into ADP and phosphate on the inside. Displays high substrate specificity and affinity

Energy

The main different forms of are proton motive force, ATP, or phosphoenolpyruvate (PEP)

Uniporter

Simple transporter, one substance in

Antiporter

Simple transporter, one substance in, different substance out at the same time

Symporter

Simple transporter, two different substances in at the same time

Phosphotransferase system in E. coli

• Group translocation, energy comes from PEP

• Glucose, fructose, and mannose are moved

1. Enz 1 takes phosphate off PEP and transfers it to HPr

2. Enz IIa and Enz IIb transfer phosphate to the end of Enz IIc

3. Glucose comes in and gets bonded to the phosphate, creating a concentration gradient of sugar

Peptidoglycan

Rigid layer providing strength to the cell wall in bacteria. Porous meshwork

NAG, NAM, and peptide bonds

Gram-positive

Cell wall is thicker but only composed of a single molecule type; peptidoglycan with teichoic acid and lipoteichoic acids embedded, and a cytoplasmic membrane with embedded proteins

Teichoic acids

In gram-positive cell walls, these are embedded to help attract cations

Lipoteichoic acids

Teichoic acids covalently bound to membrane lipids

Gram-negative

Cell wall has at least two layers; outer membrane with LPS, peptidoglycan, and a cytoplasmic membrane with embedded proteins

Mycoplasmas

Prokaryote that lacks cell walls, has cholesterol in membrane like Eukaryotes and is very waxy

LPS/Lipopolysaccharide

In gram-negative cell walls, main component in outer half of outer membrane and contains lipid A, core polysaccharide, and O-polysaccharide going from bottom to top

Endotoxin

The toxic component of LPS, attributed to lipid A

Porins

Channels for movement of hydrophilic low molecular-weight substances found on the outer membrane of gram-negative bacteria

Periplasm

Space located between cytoplasmic and outer membranes of gram-negative bacteria

Archaea

These cell walls have no peptidoglycan nor outer membrane, some have pseudomurein, but most have S-layers

Pseudomurein

In some archaea cell walls, similar to peptidoglycan

S-Layers

Found in most archaea, most common cell wall type among archaea and consists of a protein or glycoprotein

Capsule

In Bacteria, polysaccharide layers that aid in evading the immune system and help with attachment; has a tighter matrix that is often bonded to cell wall

Slime layer

In Bacteria, polysaccharide layers that aid in evading the immune system and help with attachment; loose, less connected to cell

Fimbriae

Filamentous protein structures, enables organisms to stick to surfaces or form pellicles (hair-like)

Pili

Filamentous protein structures, longer than fimbriae and facilitates genetic exchange between cells through conjugation

Flagella

Structure that aids in swimming/movement, moves by rotation where speed of rotation increases or decreases depending on the strength of the PMF (proton motive force)

Polar

Single flagellum at one pole

Lophotrichous

Tuft of flagella at one pole

Amphitrichous

Flagella at both poles

Peritrichous

Flagella all over

Amphilophotrichous

Tuft of flagella at both ends

Endospores

Cells resistant to heat, harsh chemicals and radiation, ideal for intense conditions and are only present in some gram-positive bacteria. Most studied in Clostridium and Bacillus species. Resistant to dyes and has a dehydrated core allowing high heat tolerance

Dipicolinic acid

In endospores, this is a characteristic component that aids with dye resistance

Taxis

Directed movement in response to chemical or physical gradients

Chemotaxis

Cell motion as a response to chemicals; best seen in E. coli and responds to chemical concentration sensed by chemoreceptors; run and tumble

Phototaxis

Cell motion as a response to light

Aerotaxis

Cell motion as a response to oxygen

Osmotaxis

Cell motion as a response to ionic strength

Hydrotaxis

Cell motion as a response to water