BIOL-103 Classwork 4: Cell Biology

This document presents a solved homework assignment for BIOL-103, Biology in Everyday Life, focusing on cell biology concepts. The assignment includes multiple exercises covering topics such as the structure and function of the plasma membrane, the roles of various cellular components like ribosomes and organelles, and the process of osmosis. The solutions provide detailed explanations and diagrams to aid understanding. The exercises cover identifying molecules in the plasma membrane, understanding the movement of water across semi-permeable membranes, labeling cell diagrams, explaining the importance of isotonic solutions, and describing the structure and function of membrane proteins and ribosomes. This resource is designed to help students grasp key concepts in cell biology.

BIOL-103:Biology in Everyday Life Instructor: Dr. Joelle Nader-Nasr
Fall 2016
Name: _________________________
Name: _________________________
Date :Tuesday 22nd November 2016
Name: _________________________
Name: _________________________
Classwork n°4
Exercise 1
Refer to the illustration below in order to answer the following questions
1- What is molecule C?
a. Phospholipid
b. Integrated protein
c. Cholesterol
d. Glycoprotein
2- What is the role of molecule C?
a. Facilitates the diffusion of molecules across the plasma membrane
b. Allows cell of the immune system to recognize a cell as native to the body
c. Works to keep the membrane at optimal fluidity
d. Forms the membrane by aggregating as a bilayer
3- Which molecule is both hydrophilic and hydrophobic and aggregates as a bilayer to form
the membrane?
a. C
b. D
c. E
d. F
4- What is molecule E?
a. Phospholipid
b. Integrated protein
c. Cholesterol
d. Glycoprotein
5- What is the role of molecule E?
a. Facilitates the diffusion of molecules across the plasma membrane
b. Allows cell of the immune system to recognize a cell as native to the body
c. Works to keep the membrane at optimal fluidity
d. Forms the membrane by aggregating as a bilayer
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Exercise 2
Concentration gradient – plasma membrane – rough endoplasmic reticulum – water –
organelles – ribosomes – semipermeable –cytosol – Golgi complex
1- Osmosis refers to the net movement of water across semi permeable membrane
according to a concentration gradient.
2- In a eukaryotic cell, the cytoplasm is the region that lies inside the plasma membrane.
The jelly-like fluid filling much of this region is called cytosol, while the individual
highly organized structures within it are called organelles.
3- Proteins are put together within tiny organelles called ribosomes that lie outside the
nucleus. During their production, these proteins fold up upon entering the rough
endoplasmic reticulum, where they undergo editing, after which they move to the
Golgi complex, where they undergo further editing and are sorted for distribution.
Exercise 3
Label the following diagrams
____________________ __________________
A Mitochondrion A Nucleus
B Lysosome B Nucleoplasm
C Cytoplasm C Nucleolus
D Nuclear envelope D Nuclear pore
E Rough endoplasmic reticulum E Rough endoplasmic reticulum
F Smooth endoplasmic reticulum F Microtubules
G Microtubules G Vacuole
H Secretary vesicles H Cytoplasm
I Ribosome I Storage vesicles
J Golgi apparatus J Cell membrane (coat)
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K Plasma membrane
L Mitochondrion
M Ribosome
N Golgi apparatus
Exercise 4
1- “The animal cell has always to be surrounded by an isotonic solution”. Using the
diagram below, explain why this statement is correct?
Fig-1 describes the movement of water into cell by osmosis process in order to reach
equilibrium. As a process, the cell gets swell and eventually rupture can takes place. It
happens when the salts concentration inside the cell is low.
Fig-2 shows that movement of water in to and outside the cell is same therefore the net water
content in the cell remains same and maintains its shape. It happens when the cell is placed in
a solution containing same concentration of ions or solutes. Therefore, the term isotonic is
used.
Fig-3 shows that movement of water outside of the cell in order to reach equilibrium. As a
process, the cell gets shrinked and the phenomenon is called as crenulation. It happens when
the concentration of solutes or ions is high outside the cell.
2- Describe the structure of a plasma membrane. What are the molecules forming it
and what is the general function of each?
The fundamental structure of the membrane is the phospholipid bilayer, which forms a stable
barrier between two aqueous compartments. The principal components of the plasma
membrane are lipids (phospholipids and cholesterol), proteins, and carbohydrate groups that
are attached to some of the lipids and proteins.
o A phospholipid is a lipid made of glycerol, two fatty acid tails, and a phosphate-linked
head group. Biological membranes usually involve two layers of phospholipids with
their tails pointing inward, an arrangement called a phospholipid bilayer.
o Cholesterol, another lipid composed of four fused carbon rings, is found alongside
phospholipids in the core of the membrane. Cholesterol helps to minimize the effects
of temperature on fluidity
o Membrane proteins may extend partway into the plasma membrane, cross the
membrane entirely, or be loosely attached to its inside or outside face. These are
responsible for carrying out specific membrane functions.
o Carbohydrate groups are present only on the outer surface of the plasma membrane
and are attached to proteins, forming glycoproteins, or lipids, forming glycolipids.
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Part of the role of these components is to protect the cell surface. In addition, the
oligosaccharides of the glycocalyx serve as markers for a variety of cell-cell
interactions
o The proportions of proteins, lipids, and carbohydrates in the plasma membrane vary
between different types of cells. For a typical human cell, however, proteins account
for about 50 percent of the composition by mass, lipids (of all types) account for
about 40 percent, and the remaining 10 percent comes from carbohydrates.
3- What are the five categories of proteins commonly found in plasma membranes, and
what is the function of each one?
The five categories of proteins include (i) Transport proteins (ii) Enzymes (iii) Signal
transduction proteins (iv) Recognition proteins and (v) Joining proteins. The functions of
each are provided below
o Transport proteins: These transmembrane proteins can form a pore or channel in the
membrane that is selective for certain molecules. It is also possible that they transport
molecules by changing shape. Some require energy (ATP) for this transport E.g.,
Glucose transporter
o Enzymes: Possess activity; the active site is inside the cell. These proteins can occur
as groups to facilitate a series of enzymatic processes E.g., Tyrosine kinases
o Signal transduction proteins: These proteins receive a signal from outside the cell and
convert this to a signal inside the cell. A signal molecule can for example change the
shape of the protein allowing a protein from inside the cell to bind to the receptor
E.g., G-proteins.
o Recognition proteins: Some of these proteins contain a certain 'tag' (usually a sugar)
that can be recognized by membrane proteins of other cells. This way cells can
communicate with each other (transient). The tag can also be used to differentiate
between different types of cells E.g., Glycoproteins that determine blood type.
o Joining proteins: These proteins also bind to other membrane proteins as the previous
proteins. In this case, however, the connection is tighter and lasts longer E.g., Tight
junction.
4- What is the function of ribosomes? Where in the cell are they found? Are they
limited to eukaryotic cells?
Ribosomes are a cell structure that makes protein. Protein is needed for many cell functions
such as repairing damage or directing chemical processes. Ribosomes can be found floating
within the cytoplasm or attached to the endoplasmic reticulum. The location of the ribosomes
in a cell determines what kind of protein it makes. If the ribosomes are floating freely
throughout the cell, it will make proteins that will be utilized within the cell itself. When
ribosomes are attached to endoplasmic reticulum, it is referred to as rough endoplasmic
reticulum or rough ER. Proteins made on the rough ER are used for usage inside the cell or
outside the cell. Proteins are an essential part of all cells.
No, Ribosomes are present in both prokaryotes and eukaryotes. While a structure such as a
nucleus is only found in eukaryotes, every cell needs ribosomes to manufacture proteins.
Since there are no membrane-bound organelles in prokaryotes, the ribosomes float free in the
cytosol.
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