BIOLOGY ASSIGNMENT SB015

BIOLOGY SB015 ASSIGNMENT
2022/2023

Molecules of Life
&

Cell Structures and
Functions

Name: AIRIES KIRANA BINTI MOHD KHAIRUL ALWI
Matric number: MS2113172952
Practicum: H5T02A
Set: C
Lecturer: PN. NOR SYUHAIZA BINTI NORDIN

Main type molecule of life

WATER CARBOHYDRATE

LIPID PROTEINS

DNA & RNA MOLECULES

LIPID

- Major Types of Lipids -

Contain of: TRIGLYCERIDES
(FAT & OIL)

1 Glycerol 3 Fatty Acids ester linkage

three-carbon alcohol a long, unbranched
that contains three hydrocarbon chain with
hydroxyl group (-OH) carboxyl group (-COOH)

by ester bonds

Form fats and oils mainly for energy storage

Fat (saturated) Oil (unsaturated)
Solid at room temperature Liquid at room temperature

Contain saturated fatty acids Contain unsaturated fatty acids
Solid state at room temperature SLiquid state at room temperature
Found in animals Can be found in plant and fish
No double bond between carbon atoms Has one or more double bonds between carbon atoms
which reduces the number of bonded hydrogen atoms
Formation and breakdown of Triglycerides :

LIPID

PHOSPHOLIPIDS

Two fatty acid attached to glycerol. Hydrophobic Hydrophilic
The third hydroxyl group of glycerol is joined "tails" derived from "head" containing a
to a phosphate group, which has negative fatty acids, joined by phosphate group
charge. an alcohol residue a molecule that “loves
Eg: Lecithin a molecule that water”
Component of cell membrane “hates water” it is attracted to
Contain nutrien choline found in egg yolk, it is not attracted to water molecules and
peanut, milk, soy bean. water, but will usually can usually dissolve in
dissolve in oils or fats. water.

STEROIDS

Many hormone as well as cholesterol are steroids, which are lipids characterized by a carbon
skeleton.
A biologically active organic compound.
Have basic four fused carbon rings hydrocarbon structure.
Eg: Cholesterol (component of cell membrane)
Eg: Testosterone (precursor for sex hormone)

Cholesterol Testosterone

PLASMA MEMBRANE

Fluid Mosaic model is propose by Singer and Nicolson
Fluid because phospholipids and proteins are able to move side by side in the phospholipids bilayer.
Mosaic because arrangement of different proteins partially or fully embedded attached to the phospholipids
bilayer.

Two main components of plasma membrane are phospholipids and
proteins
Phospholipids are amphipathic molecules that means have both hydrophobic
and hydrophilic regions :
- hydrophilic head
- hydrophobic tail

Importance of hydrophobic regions in plasma membrane :
- allow the cell membrane to be selectively permeable
- allow movement of lipid soluble molecules
- reduce loss of water from inside cell

Cholesterol are found in plasma membrane of animal cells
between the tails of phospholipids
Function of cholesterol is to regulate fluidity of membrane
under the influence of temperature - reducing fluidity of
membrane / membrane less fluid at warm/ higher
temperature - membrane more fluid at lower temperature

PLASMA MEMBRANE
Two types of membrane proteins :
- intrinsic @ integral protein (either fully or partially embedded in phospholipids bilayer)
- peripheral @ extrinsic protein (attach to phospholipids bilayer)

- as transport protein - as enzymes - involve in signal transduction
/ as cell surface receptor
Channel protein and Has specific active site that Act as receptor that has
carrier protein (for binds with specific specific binding site for
passive ransport) substrate during signaling molecule e.g.
hormone

- as enzymes

- as cell surface identity marker - as intercellular joining / - provide attachment
or involve in cell recognition involve in cell adhesion site for cytoskeleton and
Membrane proteins of extracellular matrix
as cell surface neighboring cells are joined
identity marker or together forming tissue Helps to maintain cell
involve in cell e.g. epithelial cells shape and to stabilize
recognition location of certain
membrane proteins

Carbohydrate chains attach to protein forming glycoprotein
e.g. variation in carbohydrate chain of glycoproteins on the surface of RBC contribute to

▪the 4 human blood types A, B, AB and O)
Importance of membrane carbohydrates in cell-cell recognition :
- sorting of cells into tissues and organs in animal embryo
- basis for rejection of foreign @ non-self tissue by immune system
- enable cell recognize other cell by binding to molecules containing carbohydrates on extracellular surface of
plasma membrane.

The structure of the fatty acid tails of
the phospholipids is important in determining
the properties of the membrane, and in

particular, how fluid it is.

Saturated fatty acids have no double bonds so they are relatively straight
Unsaturated fatty acids, contain one or more double bonds, often resulting in a
bend or kink.
The saturated and unsaturated fatty acid tails of phospholipids behave
differently as temperature drops:

At cooler temperatures, the straight tails of saturated
fatty acids can pack tightly together making a dense and
fairly rigid membrane.

Phospholipids with unsaturated fatty acid tails cannot pack
together as tightly because of the bent structure of the
tails. Because of this, a membrane containing unsaturated
phospholipids will stay fluid at lower temperatures than a
membrane made of saturated ones.

Cholesterol, another type of lipid that is embedded among the phospholipids of
the membrane, helps to minimize the effects of temperature on fluidity.
At low temperatures, cholesterol increases fluidity by keeping phospholipids
from packing tightly together, while at high temperatures, it actually reduces
fluidity
In this way, cholesterol expands the range of temperatures at which a
membrane maintains a functional, healthy fluidity.