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Cell Biology
Introduction to Cells

CELL BIOLOGY
INTRODUCTION TO
CELLS
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Notes
Highlighting scheme ●

Important words

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Important phrases

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Definitions

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Explanations

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Important statements

UNIT 1
...
Cell Theory
a
...


From the 17th century, biologists began to examine plant and animal
tissues using microscopes
...
A
theory was devised to explain these common basic structural features
known as the Cell Theory
...


The Cell Theory states that1
...

2
...

a
...
The cell is the smallest functional and fundamental unit of life
...


The Cell Theory is still considered a theory because it cannot be
disproven
...


b
...


All cells contain or house genetic material, which carries the instructions
for its cellular activities
...


The majority of the cellular activities (chemical reactions) are catalyzed
by the enzymes produced by the cell
...


All living cells are surrounded by a cellular membrane
...


iv
...


c
...

i
...
Striated Muscle Cells- Striated Muscle Cells facilitate movement
...
They also carry their own genetic material and have
their own power-release system
...
3mm)
...

a
...

2
...

They usually consist of one cell, yet they can grow to large sizes
...
This challenges the notion that
cells are the smallest functional unit of life, as any large organism
is expected to be multicellular
...
Aseptate Hyphae- Ask Mr
...
Functions of Life
a
...


All living organisms carry out several functions that are necessary for its
survival
...
Metabolism -refers to the sum of all the chemical reactions that
take place inside the cell
...
Reproduction -refers to the ability of an organism to produce
offspring
...
Growth -refers to an irreversible/ permanent increase in size(dry
mass)
...
Response -refers to the ability to identify and respond to internal
and external stimuli
...
Homeostasis -refers to the process of maintaining a constant
internal environment
...
Nutrition- refers to the process of obtaining food in order to
provide energy such that the organism can function and grow
...
Excretion- refers to the ability to get rid of the waste products
created by metabolism
...
Cell Size

a
...


The Arctic fox is twice the size of the Fennec fox
...
The metabolic rate of the cell is directly
proportional to its volume
...
The rate of chemical reactions of a cell is directly proportional to
the volume of the cell
...
Why are regular cells microscopic in size?
i
...
What this means is that the rate at which substances
cross the cell membrane depends on the surface area of the cell
...

1
...


c
...

i
...
It also has reduced ears such
that it’s body loses heat at a slower rate due to the cold climatic
conditions it lives in
...


ii
...
They are
smaller than Polar Bears, and their small size helps them lose heat
...


iii
...


4
...
What is Cell Differentiation?
i
...

This is known as the division of labour
...


Cell Differentiation, also known as Cell Specialisation, refers to the
development of cells in different ways such that they can carry out
specific functions
...


iii
...
Therefore, the
key to development lies in the control of genetic expression
...


It allows the tissues to carry out their roles more efficiently than if they
had many different functions
...


b
...


For example, the rod cells and the lens cell of the eye both contain the
gene that gives them the ability to produce a pigment that absorbs light,
however it is only expressed in the rod cells
...
And if the
lens cell did express this gene, less light would pass through the lens and
would blur clarity
...


Another example of differentiation would refer to the olfactory receptor
cells which are only expressed in the skin inside the nose
...

This is how we can distinguish between so many smells
...
Stem Cells
a
...


Stem cells are those cells which have the ability to differentiate into many
different types of cells
...
The sperm fertilizes an egg cell to produce a zygote
...

2
...

3
...


b
...


Stem cells have two key properties1
...

a
...

2
...


c
...

i
...

1
...


2
...

3
...

ii
...
Production of striated muscle fibres, or meat for human
consumption
...
During embryonic development, the cells must commit themselves to a pattern
of differentiation
...
Though they can still divide, they will only differentiate in the same
way and thus, will no longer be stem cells
...
Does the human body have stem cells?
i
...
They have the ability to regenerate and repair
...


UNIT 1
...
Prokaryotes and their structure
a
...


Prokaryotes are unicellular organisms that lack a nucleus
...


Instead of a nucleus, prokaryotes have a nucleoid region where
the genetic material is located
...
Describe the structure of a prokaryotic cell
...


Though they are structurally less complex than eukaryotes, prokaryotes
are biochemically complex
...
Prokaryotes are unicellular organisms that lack a nucleus
...

2
...
It has no histones attached to it
...


3
...
However, this
circular piece of DNA can be copied/exchanged/changed
...

4
...
The cytoplasm is the medium for biochemical
reactions
...
A prokaryotic cell lacks cell organelles apart from ribosomes
(Svedberg, 70S)
...
These organisms are encapsulated not only by a cellular
membrane, but also by a cell wall that contains peptidoglycan
...
This cell wall protects the prokaryotic cells from the
external environment, helps it maintain its shape and
prevents it from bursting
...
It is said to be “extracellular”
...
They also have a capsule, which is outside of the cell wall, which
offers them protection
...
The theory states that the capsule goes soft in the summer,
and that is why they can be killed easily by the White blood
cells
...

However, these capsules harden in the winter, and thus are
harder to kill by WBCs, and that is one of the reasons as to
why we are more prone to fall ill in cold climates
...
The cell membrane helps in the regulation of the entry and exit of
materials in the cell
...
For movement, prokaryotic cells have Flagella
...
For communication as well as the exchange of materials, the cells
have Pili which are also what they use for response
...


7
...
What are eukaryotic cells?
i
...


b
...


Organelles are the compartments within the cytoplasm
...


c
...


Compartmentalisation can be found in eukaryotic cells, where the cell is
partitioned into multiple compartments by single or double membranes
...


The compartments in the cytoplasm are known as organelles, and they
have a definite structure and function
...


The advantages of compartmentalisation are as follows1
...

2
...

3
...

a
...

4
...


d
...

i
...
It is the region where
all organelles are found
...
Cytosol is the liquid part of the cytoplasm
...


ii
...

1
...

2
...

3
...
For
example, striated muscle cells have more mitochondria as they
require more energy ( facilitate movement)
...
A lot of mitochondria is also found in the sperm cells as
they need to swim to reach the egg in around 8 hours
...
Mitochondria has its own 70S ribosomes
...
It also has its own circular naked DNA known as mDNA
...
mDNA is the only DNA that hasn’t changed for multiple
years
...


Ribosomes- are organelles that lack a membrane, and facilitate protein
synthesis
...

1
...
70S- Found in the mitochondria
...
80S- Found in the cell of eukaryotes
...
They are constructed in a region of the nucleus known as the
nucleolus
...


Endoplasmic Reticulum- Extensive network of tubes and channels
...
There are two types of ER- smooth
and rough endoplasmic reticulum
...
The smooth endoplasmic reticulum does not have ribosomes
attached to it
...

a
...

b
...

2
...

The ribosomes produce proteins according to the DNA
...
This is why they are close to the nucleus, as the nucleic
DNA must send messages as to what proteins are to be
synthesized
...
The rough endoplasmic reticulum deals with the synthesis,
modification, storage and transportation of proteins
...
Protein synthesises- cisternae- vesicles-golgi apparatus
...


Golgi Apparatus- An organelle that consists of flattened membrane sacs
known as the cisternae
...
They aren’t near the nucleus and are the distribution centre of the
cell
...
The site where the vesicles join- CIS side
...
Site where vesicles leave- TRANS side
...


Nucleus- Is a double membraned structure that contains or houses the
genetic material, DNA
...
DNA is the unit of inheritance and is compartmentalised in the
nucleus
...
The nucleus is where DNA is replicated and transcribed to form
mRNA, which is exported via the nuclear pores to the cytoplasm
...
The nucleus has a nuclear pore which allows for communication
with the rest of the cell
...


Vacuoles- Organelles that are single membraned with fluid inside
...
They are small and temporary in
animal cells
...

1
...

2
...


viii
...


Vesicles- tiny vacuoles used to transport materials within the cell
...
They
are made up of microtubules and play an important role in cell division
...


Lysosomes- Lysosomes are also known as intracellular digestive centres
...

They are only found in cells
...
They are the site of cell digestion and helps in breaking down
hormones with the help of digestive enzymes known as hydrolytic
enzymes
...
They carry out hydrolysis by breaking down organic molecules
such as proteins, carbohydrates, lipids and nucleic acids
...
They also digest damaged organelles or cells
...
They contain a high concentration of protein which is why they
are densely stained on electron micrographs
...


Chloroplast(EXCLUSIVE TO PLANT CELLS ONLY)- Chloroplast is a
double membraned cell organelle that contains chlorophyll, which is a
pigment that absorbs light and facilitates photosynthesis
...
Chlorophyll can be found in the thylakoid, which are flattened
sacs of membrane
...
It has its own circular genetic material and has ribosomes
...
(They also produce glucose and a wide variety of organic
compounds by photosynthesis
...
Starch grains may be present inside chloroplasts if they have been
photosynthesizing rapidly
...
Evaluate Eukaryotes and Prokaryotes
...

Both carry out all functions of
life
...


DNA without histones

DNA with histones

Has no organelles except
ribosomes-not
compartmentalised

Has all organellesinternally
compartmentalised

70S ribosomes

80S ribosomes

Differentiate between Plant and Animal Cell
...
What are different cell membranes and walls made up of?
i
...


Plants-cell walls- cellulose
Algae-cell wall/outermost layer-cellulose

iii
...


All other fungi-chitin cell wall

v
...


Animals-cell membrane-phospholipids and glycoproteins
...
3
1
...
Why do we eat Lipids?
i
...
The reason we eat lipids is so that our body can make
cell membranes
...


A phospholipid molecule is made up of one glycerol and two fatty acid
chains
...


b
...

i
...
They are made up
of one glycerol and two fatty acid chains
...


ii
...
While the lipid is hydrophobic in nature and
thus repels water
...


Due to its amphipathic properties, the phospholipids form a bi-layer, with
the hydrophilic parts facing outwards/the water , and the hydrophobic
parts facing inwards and towards each other because the hydrocarbon
tails are attracted to each other
...


c
...


The phospholipid kink also allows for a very important property that is
desirable for a membrane- flexibility
...

1
...


ii
...
Cholesterol allows them to be
flexible and prevents rigid packing
...
Cell Membrane Models
a
...


In the 1920s, Gorter and Grendel extracted phospholipids from the
plasma membrane of red blood cells
...
They
realised this was twice as large as the area of the plasma membrane
...


ii
...


b
...


The 1930’s Davson-Danielli’s model suggested that the cell membrane
was like a sandwich- two protein bands were located at the top and the
bottom of the phospholipid bilayer, and this explained the reason as to
why the cell membrane, despite being so thin was an effective barrier to
the movement of some substances
...


The electron micrographs of the cell membrane in the 1950’s showed a
railroad track appearance
...
Proteins appear dark and the phospholipids
appear light in electron micrographs, so at the time, its appearance
supported the Davson Danielli Model of the cell membrane
...
How did the Singer-Nicolson Model change the perception of the Cell
Membrane?

i
...
It also meant that the
proteins had the ability to move, and weren’t rigid
...


It’s name comes from the idea that it looks like a mosaic, and the fluidity
of the cell membrane
...
Cell Membrane and Proteins
a
...


In the 1950s and the 1960s, evidence accumulated such that it questioned
the Davson Danielli model1
...
If the Davson Danielli
model was true, then the scientists should have observed a layer
of phospholipids and a layer of fat above or below it
...
There was no uniform protein layer
...
Structure of the membrane proteins- Improvements in
biochemical techniques allowed for proteins to be extracted from
the membranes
...
Moreover, these proteins
were hydrophobic in nature, and thus would be attracted to the
hydrocarbon tails of the phospholipids located in the centre of the
membrane
...
What are the functions of the proteins in the Cell Membrane?
i
...
The first one is
the Peripheral Protein- this protein is embedded on the surface of the
membrane and does not go across the whole bi-layer
...


ii
...
Site of hormonal binding
...
It allows for enzymatic actions by acting as an enzyme to help
break things down
...
It acts as a cell adhesive and holds cells together
...
They act as channels and pumps for passive and active transport
...
Cell-to -cell communication such as receptors for
neurotransmitters at synapses
...
4
4
...
What is Passive Transport and what are the different types of passive transport
seen in the human body?
i
...


ii
...


b
...


Diffusion can be defined as the net movement of molecules from an area
of higher concentration to an area of lower concentration
...


ii
...


iii
...
If the
concentration of oxygen is higher outside of the cell, than inside the cell
due to aerobic respiration, then the oxygen molecules will diffuse into the
cell between the phospholipid bi-layer membrane
...


iv
...
Polar molecules, which have partial

negative/positive charges over their surface, can diffuse at low rates
between the phospholipid membrane
...
Small polar molecules such as urea and ethanol can diffuse more
easily than larger particles
...
What is Osmosis?
i
...
One can also say that it is the net
movement of water molecules from an area with high water potential to
an area with low water potential
...


ii
...

Substances dissolve in water by forming intermolecular bonds with water
molecules
...

Therefore, an area with a higher solute concentration has a lower
concentration of water and vice versa
...


iii
...
Even though the bi-lipid layer is
hydrophilic, the water molecules are small enough to pass through the
phospholipid layer
...
What are aquaporins?
i
...
It
makes the cell membrane more permeable to water
...
Kidney cells, root hair cells
...
Explain the following termsi
...


ii
...


iii
...
The cell does not burst because of the cell wall and the vacuole, which
absorbs majority if not all of the water
...


Flaccid- This term refers to when water leaves the plant cell and the
membrane and the vacuole shrink in size
...


f
...

i
...


ii
...
Therefore, they are diffused via protein
channels
...
Active Transport
a
...


Active transport can be defined as the movement or transport of materials
in the body with the use of energy/ ATP molecules
...
Sodium-Potassium Pumps, endocytosis, exocytosis
...
How do protein pumps work?
i
...


ii
...
A conformational change takes place using the energy from ATP
in the protein
...


c
...


Vesicles are extremely dynamic in nature
...
This is possible because membranes are
fluid, and allow structures surrounded by a membrane to change their
shape and move
...


To form a vesicle, a part of the membrane is pulled from the rest of the
membrane, and pinched off
...


d
...


Endocytosis is a method of active transport
...
In this manner, the plasma membrane transports materials
that cannot pass through it
...


For example, in the placenta- the foetus absorbs proteins from the
mother’s blood (as well as antibodies) through endocytosis
...


Amoeba and Paramoecium both take in undigested food particles through
endocytosis
...


Moreover, WBC attacks bacteria and viruses via endocytosis
...
What is exocytosis?
i
...
Vesicles from the interior of
the cell fuse with the cell membrane such that the contents inside the
vesicle are expelled outside of the cell
...


f
...

i
...
Rough endoplasmic reticulum and the Golgi apparatus both use
endocytosis and exocytosis
...


Differences1
...


Modified proteins exit through
ER by exocytosis
...
5
6
...
What is Spontaneous Generation? What were the expeditions to support it?
i
...


ii
...


iii
...


iv
...


b
...


Franceso Redi showed that maggots only developed in rotting meat if
flies were allowed to come in contact with it
...
Maggots arose from insects, not from decaying matter
...


Lazzaro Spallanzani boiled soup in eight containers
...
Organisms grew in the containers
left open, but not in the ones that remained closed
...
“Spontaneous generation could occur if the matter had contact
with air”
...
How did Pasteur’s experiment disprove the Spontaneous Generation Theory?
i
...
Pasteur created a broth (nutrient-rich medium) and filled
his samples in flasks with long necks
...


ii
...


iii
...
Pasteur
realised that though the boiled broths were in contact with air, there was
no spontaneous generation occurring
...


Then, Pasteur snapped the necks of some of the flasks, such that they
were shorter but vertically necked flasks
...


v
...


7
...
Explain in short the Urey- Miller Experiment
...


The Urey- Miller experiment was based on the notion that life could arise
from nonliving matter under certain circumstances
...


The experiment aimed to show that under certain environmental
conditions, organic molecules can originate from inorganic matter
...
Hydrothermal vents are their own ecosystem that don’t rely on
the sun
...
Shallow seas and geysers- hot and nutrient rich water
...
Volcanoes- heat, energy, inorganic material
...
Comets- 20% of its tail is organic material
...


Urey and Miller aimed to create an experimental set-up that mocked
Earth’s atmosphere and living conditions
...
They also used
electrical discharges to create a lightning simulation
...


8
...
What is the endosymbiosis theory?
i
...
It believes that prokaryotic cells (small and large) were in a
mutualistic relationship
...

1
...


Basically, a larger prokaryotic cell ingested a smaller prokaryotic cell via
endocytosis
...
As long as the digested prokaryotes grew and multiplied at the
same rate as the bigger one, then they could survive inside the larger cell
indefinitely
...
Give evidence that mitochondria and chloroplast were both once prokaryotes
...

ii
...

Both have 70S ribosomes and thus synthesise their own proteins
...


Both are double-membraned, similar to bacteria
...


Both have similar build to prokaryotes
...


Both reproduce via fission, like a prokaryotic cell and can divide
independently of the host cell
...
6
1
...
What is Interphase?
i
...


b
...


The cell life cycle can be divided into four main categories- the G1 Stage,
the Synthesis stage, the G2 phase
...
When does Cytokinesis begin?
i
...


d
...


Mitosis can be defined as the process by which the nucleus of a eukaryotic
cell divides genetically into two identical nuclei
...


ii
...


iii
...


e
...

ii
...

Synthesis phase1
...
Then, when it divides
eventually, it has enough DNA for both daughter cells
...


G2 Phase1
...

a
...
Plant cells also synthesize
cellulose and use vesicles to add it to their cell walls
...
The DNA condenses from chromatin to chromosomes
...
The cell prepares for cell division
...
Cyclins
a
...


Cyclins are proteins that act as phase indicators
...


b
...


Cyclins control the cell cycle and ensure that cells divide when new cells
are needed, and not at other times
...


ii
...
This triggers Cell Division
...
When enough MPF is formed, Cell Division is triggered
...


Once Cell Division is complete, MPK breaks down to form CDK and M
...


iv
...
This begins the
synthesis phase
...
The G1 Cyclin is broken down by the body

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