PRE-MID ASSIGNMENT#1

SUBMITTED TO: Dr. AMNA YOUNUS

SUBMITTED BY: TAUREED ZAHRA KAZMI

SAMMAR FATIMA

SANA ALTAF

COURSE TITLE: INTRODUCTION TO BIOCHEMISTRY

SECTION: A

DATE: 7 FEBRUARY 2023.

KINNAIRD COLLEGE FOR WOMEN, LAHORE.

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 Topic: Gram-positive and Gram-negative Bacteria

Bacteria:

Prokaryotic cells, which lack a proper nucleus, are a huge category of tiny, unicellular,

microscopic creatures known as bacteria. The rudimentary physical structure of these tiny

creatures includes a cell wall, capsule, DNA, pili, flagellum, cytoplasm, and ribosomes.

According to the techniques used for staining, bacteria might be either gram-positive or

gram-negative.

Gram-Positive and Gram-Negative Bacteria – Overview

While gram-negative bacteria lose crystal violet and stain red, gram-positive bacteria retain

crystal violet and tint purple. Gram staining may thus be used to distinguish between the two

kinds of bacteria. Due to their thick cell walls, gram-negative bacteria are more resistant to

antibodies.

Based on their capacity to retain the gramme stain, bacteria are divided into gram-positive

and gram-negative groups. Gram-negative bacteria are stained by a counterstain like

safranin, and the alcohol wash helps to remove that stain. As a result, they are clearly pink in

colour when viewed under a microscope. On the other hand, gram-positive bacteria maintain

the gramme stain and exhibit a discernible violet colour when iodine and ethanol are applied

(alcohol).

The cell wall of gram-positive bacteria is mostly made up of several layers of peptidoglycan,

which together create a thick and robust structure. Teichoic acids and phosphate are other

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compounds found in its cell wall. There are two different forms of teichoic acids found in

gram-positive bacteria: lipoteichoic acid and teichoic wall acid.

The cell wall of gram-negative bacteria is composed of peptidoglycan layers and an outer

membrane. Lipopolysaccharides (LPS), phospholipids, and lipoproteins make up the outer

membrane. Between the plasma membrane and the outer membrane, in the fluid-like

periplasm, the peptidoglycan adheres to lipoproteins of the outer membrane and maintains its

integrity. The periplasm is packed with proteins and degrading enzymes which aid in moving

materials.

Unlike gram-positive bacteria, gram-negative bacteria's cell walls do not contain teichoic

acid. The outer membrane is permeable to nutrients, water, food, iron, etc. because porins are

present.

Difference between Gram-Positive and Gram-Negative Bacteria – Key Points

 Thick layers of peptidoglycan make up the gram-positive bacteria's cell wall.

 Thin layers of peptidoglycan make up gram-negative bacteria's cell wall.

 Gram-positive cells maintain the purple stain after the gramme staining technique.

 Gram-negative cells do not maintain the purple stain after the gramme staining

technique.

 Exotoxins are produced by gram-positive bacteria.

 Endotoxins are produced by gram-negative bacteria.

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 Difference between Gram-Positive and Gram-Negative Bacteria

Gram-Positive bacteria Gram-Negative bacteria

Cell Wall

A single-layered, smooth cell wall  A double-layered, wavy cell-wall

Cell Wall thickness

The thickness of the cell wall is 20

Peptidoglycan Layer

It is a thick layer/ also can be

Teichoic acids

Presence of teichoic acids Absence of teichoic acids

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 Outer membrane

The outer membrane is absent The outer membrane is present (mostly)

Porins

Absent Occurs in Outer Membrane

Mesosome

It is more prominent. It is less prominent.

Morphology

Cocci or spore-forming rods Non-spore forming rods.

Flagella Structure

Two rings in basal body Four rings in basal body

Lipid content

Very low 20 to 30%

Lipopolysaccharide

Absent Present

Toxin Produced

Exotoxins Endotoxins or Exotoxins

Resistance to Antibiotic

More susceptible More resistant

Examples

Staphylococcus, Streptococcus, etc. Escherichia, Salmonella, etc.

Gram Staining 

These bacteria retain the crystal These bacteria do not retain the stain colour even after
violet colour even after they are they are washed with acetone or alcohol and appear as
washed with acetone or alcohol and pink-coloured when examined under the microscope after

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 appear as purple-coloured when
examined under the microscope gram staining.
after gram staining.

Difference between Animal cell and Plant cell

Plant cell Animal cell

Cell shape

Square or rectangular in shape Irregular or round in shape 

Cell Wall

Present Absent

Nucleus

Present and lies on one side of the

References
Rath, S. (2019). Major Difference Between Gram-Positive and Gram-Negative Bacteria.

BYJUS. https://byjus.com/biology/difference-between-gram-positive-and-gram-negative-

bacteria/

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