Biology Assignment

MOLECULES OF LIFE AND CELL STRUCTURES
AND FUNCTIONS

SET C QUESTION

NAME : WAN ADRIANA BINTI MOHD NAZRY

PRACTICUM : H8T04A

MATRIX NO. : MS2213104816

QUESTIONS

1. State the main types of molecules of life.
2.Classify lipids into three main types based on their structure

and characteristics
3.Plasma membrane of cells consists of lipids and some other

organic molecules. With the aid of a labeled diagram, briefly
describe the structure of plasma membrane.
4. Explain how certain type of lipids ensures the fluidity of the
plasma membrane while some other type of lipids may
reduce its fluidity.

State the main types of molecules of life.

The main types of molecules of life are water, carbohydrates,
lipids, proteins, also DNA and RNA molecules

Classify lipids into three main types based on their
structure and characteristics .

Three main types of lipids are triglycerides, phospholipids and steroids.
Triglyceride formed by 3 fatty acids and 1 glycerol. Each fatty acid joins to
glycerol by condensation reaction then, three water molecules are
removed. The hydroxyl (OH) from carboxyl end of fatty acid and hydrogen
from the hydroxyl group of glycerol are removed. Three ester linkages are
formed. The first reaction yields a monoacylglycerol, the second reaction
yields a diacylglycerol, and the third reaction yields a triacylglycerol. There
are two types of triglycerides which are fat and oil. Fat is solid at room
temperature whereas oil is liquid at room temperature.

Next, phospholipid is composed of a glycerol backbone attached on
one end to two fatty acids and the other end has the esterified
phosphoric acid and an organic alcoholic group. Characteristically, a
phospholipid molecule has a polar head group and a non-polar tail
group. The fatty acid chains form the hydrophobic or lipophilic or non-
polar tail whereas the esterified phosphate group forms the
hydrophilic or polar head group. Phospholipids are amphipathic or
amphiphilic lipids, the non-polar fatty acid tails make phospholipid
hydrophobic whereas the polar head makes phospholipid hydrophilic.

When these phospholipidic
molecules are exposed to a lipidic
or non-polar environment,
phospholipid tails and head self-
assemble in reverse fashion to
form reverse-micelles, the fatty
acid tails which are non-polar
move towards the non-polar
molecule.

Lastly, steroid has functional groups attached to
the rings determine the types of steroid. A
cleavage of one of the rings in steroid produces
secosteroidal compounds which make the
steroids hormones control endocrine systems and
regulate metabolic pathways. For example,
cholesterol which us component in cell membrane
is precursor for sex hormone namely
testosterone.

Plasma membrane of cells consists of lipids and some other organic molecules. With
the aid of a labeled diagram, briefly describe the structure of plasma membrane.

The fluid mosaic model was proposed by S.J. Singer and Garth L. Nicolson. The fluid
mosaic model of the cell membrane is how scientists describe what the cell
membrane looks and functions like, because it is made up of a bunch of different
molecules that are distributed across the membrane. Based on the diagram, plasma
membrane is composed of bilayer of phospholipids with globular proteins
embedded in the bilayer, phospholipids and protein can move laterally. Proteins are
embedded in the phospholipid bilayer like the mosaic tiles embedded in mortar.

Plasma membrane accounted for the amphipathic characteristics of
phospholipids and proteins. Amphipathic molecules have both the hydrophilic
head of phospholipids facing outwards and attracted to the aqueous surrounding
meanwhile, the hydrophobic tails of phospholipids facing inwards.
Besides, there are two types of proteins in plasma membrane which are integral
and peripheral. Integral proteins partially embedded or fully embedded whereas
peripheral proteins attached to the outer and inner surfaces of the membrane.

Structure of plasma membrane

Furthermore, carbohydrate chain also known as oligosaccharides play important role to protect
plasma membrane by functioning as cell identity markers and recognition. Carbohydrate chain
found on the external surface of the plasma membrane such as glycoprotein which is when
carbohydrate chain attaches to protein and glycolipid is when carbohydrate chain attaches to
phosphoslipis.

Lastly, one of the most important component in plasma membrane is cholesterol because it
helps to increase flexibility and stabilizes the membrane structure by regulating the fluidity of
the membrane. Cholesterol can be found between phospholipids. At moderately warm
temperature, cholesterol reduce membrane fluidity by preventing free movement of
phospholipids molecules whereas at cool temperatures, cholesterol prevent close packing pf
phospholipids and slow down solidification.

Explain how certain type of lipids ensures the fluidity of
the plasma membrane while some other type of lipids

may reduce its fluidity.

Phospholipids are one of the main component of plasma membrane due to its
function that can ensure the fluidity of the plasma membrane. Phospholipids and
proteins can move laterally. The hydrophilic heads of phospholipids facing outwards
and attracted to aqueous while the hydrophobic tails of phospholipids facing inwards.

The other type of lipid that vital to ensure the fluidity of plasma membrane is
cholesterol. Cholesterol found between phospholipids. It helps to increase flexibility
and stabilises the membrane structure by regulating the fluidity of membrane.

Cholesterol stabilises the membrane structure at moderately warm temperature by
reducing membrane fluidity by preventing free movement of phospholipids molecules

References

Biology Online Editors, June 11th 2022, Phospholipids https://www.biologyonline.com/dictionary/phospholipid
Anonymous, (n.d.), Steroids
https://saylordotorg.github.io/text_the-basics-of-general-organic-and-biological-chemistry/s20-04-steroids.html

O. David Sparkman, Fulton G. Kitson, 2011, Steroid
https://www.sciencedirect.com/topics/chemistry/steroid#:~:text=In%20general%2C%20the%20steroid%20core,ty
pe%20of%20compound%20%5B2%5D

Khan Academy, (n.d.), Structure of Plasma Membrane
https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/plasma-membranes/a/structure-
of-the-plasma-membrane

Khan Academy, (n.d.), Fluid Mosaic Model : Cell Membranes Article https://www.khanacademy.org/science/ap-
biology/cell-structure-and-function/membrane-permeability/a/fluid-mosaic-model-cell-membranes-article

Kelly, Karen and Rene Jacobs Phospholipid Biosynthesis Plant Triacylglycerol Synthesis AOCS Lipid Library
https://www.thoughtco.com/phospholipids-
373561#:~:text=Phospholipids%20are%20very%20important%20molecules,cell%20through%20endocytosis%20and
%20exocytosis