Bacterial Structure and Functions

 bacteria are prokaryotic cells that play

an important role in human disease and

health they can cause disease but are

also part of the human microbiota and

live on our skin body and on every

day

objects in our environment when compared

to eukaryotic cells the structure of

bacteria is less complex due to a lack

of nucleus and membrane-bound organelles

such as mitochondria endoplasmic

reticulum and Golgi complexes

now bacterial cells are often surrounded

by several layers which are collectively

called the cell envelope let's start

with the cell wall which is found on the

outer surface of the cell membrane and

its most important role is to protect

the bacteria it consists of

peptidoglycan which usually helps

differentiate whether bacteria are gram

positive or gram negative gram positive

bacteria have a single thick layer of

peptidoglycan above the plasma membrane

which allows them to retain the staining

dye and gram-negative bacteria have a

thinner layer of peptidoglycan

sandwiched between the surface membrane

and the plasma membrane so they can't

retain the dye

additionally the cell wall helps

maintain their shape the round shaped

bacteria are called Cox I the rod shaped

ones are called bacilli spiral shaped

ones are spiral and sometimes the same

bacteria can have multiple forms in

which case they're called pleomorphic

some bacteria are covered by a capsule

which acts as a shield that protects the

bacteria against phagocytosis and also

helps the bacteria adhere to surfaces

the capsule is considered an important

virulence factor since the strains that

Lakha capsule are less virulent

underneath the bacterial cell wall

there's the plasma membrane which is the

most important layer because it encloses

the cytoplasm which is a gel-like

substance composed mainly of water that

also contains cell components enzymes

and various organic molecules if the

plasma membrane is removed the cell's

contents spill into the environment and

the cell no longer exists

now the plasma membrane is responsible

for most of the cells relationship with

the outside world by acquiring nutrients

and eliminating waste and also maintains

the interior of the bacteria in a

constant highly organized state usually

all plasma membranes are selectively

permeable barriers which allow certain

ions and molecules to pass in and out of

the cell while preventing the movement

of others however in bacteria the plasma

membrane has other important roles such

as respiration photosynthesis and the

synthesis of lipids and cell wall

components

now in the bacterial cytoplasm there are

scattered cell components such as

ribosomes which are the sites of protein

synthesis these ribosomes can be found

spread all over the cytoplasm where they

produce proteins that are destined to

remain inside the cell or they can be

attached to the plasma membrane and they

are called plasma membrane associated

ribosomes and in this case they make

proteins that will reside in the cell

envelope or get transported outside the

cell

another structure found in the cytoplasm

is the nucleoid which is an irregularly

shaped region that contains the cell's

chromosome the chromosomes of most

bacteria are a single circle of

double-stranded DNA but some bacteria

can have a linear chromosome while

others can have more than one chromosome

and these chromosomes contain the genes

needed to provide instructions for

protein synthesis in the cell

additionally to the genetic material

contained within the nucleoid many

bacteria contain extra chromosomal DNA

molecules called plasmids these plasmids

are small double-stranded DNA molecules

that can exist independently of the

chromosome and they can be circular or

linear plasmids have relatively few

genes and their genetic information is

not essential to the bacterium and cells

that lack them usually function normally

however plasmids often contain genes

that confer a selective advantage to the

bacterium such as resistance to

antibiotics

finally the bacteria can move or attach

to other cells and surfaces with the

help of structures that can be found on

their external surface so they have pile

I which are hair like structures that

allow them to attach to other cells and

when these are shorter

they're called fimbriae and help the

bacteria attach to surfaces they can

also have flagella which are long

whip-like protrusions that allow the

bacteria to move

all right as a quick recap the bacteria

are prokaryotic cells that play an

important role in human disease and

health and can be found almost anywhere

in the environment bacterial cells are

often surrounded by several layers which

are collectively called the cell

envelope they have a cell wall which

protects the bacteria determines whether

they are gram positive or gram negative

bacteria and also helps maintain their

shape some bacteria can also have

another extra layer on top of the cell

wall called a capsule which is a major

virulence factor underneath the cell

wall there's the plasma membrane which

is the most important layer because it

encloses the cytoplasm and defines the

cell having important roles such as

respiration photosynthesis and the

synthesis of lipids and cell wall

constituents the cytoplasm contains

ribosomes which are the site of protein

synthesis the nucleoid which contains

the genetic material and plasmids which

contain genes that confer a selective

advantage to the bacterium