Biology 2 The cell of the basis of life

What are all living organisms made from?

From cells! And all cells are from pre-existing cells

Three principles of cell theory

1. all living organisms are made of one or more cells (bacteria → one cell, humans → many cells)

2. Cell is basic structural & functional unit of life (all organs are made from it)

3. All cells from pre-existing cells

Why are viruses unusual?

Viruses NOT MADE OF CELLS (non-cellular). They contain: genetic material (DNA or RNA), protein coat (capsid) & sometimes lipid envelope → they need a host cell to reproduce

Unlike cells, what are other things viruses don’t have or are not?

1. no cytoplasm

2. no ribosomes

3. no organelles

4. can’t produce their own energy

5. not considered living organisms

What must viruses do to reproduce?

To infect a host cell

Viruses and function of their DNA or RNA, capsid protein coat, lipid envelope

DNA&RNA: carries information in oder to make new viruses

Capsid protein coat: surrounds DNA/RNA as protection, helps virus to attach host cell

Lipid envelope (some viruses): outer layer made from lipid membrane & viral proteins (example: Influenza, HIV, Corona)

Process virus reproduction

1. virus binds to host cell surface (receptors)

2. virus enters host cell

3. Cell is used to make viral genomes and parts (replication virus uses ribosomes, enzymes&energy of host cell)

4. new virus particles are put together inside cell

5. many newly made viruses spread away from the infected cell

Why do viruses infect specific type of cells?

viral surface proteins must match receptors on the host cell

Example of viruses

Virus	Genetic Material	Disease
Influenza virus	RNA	Flu
HIV	RNA	AIDS
SARS-CoV-2	RNA	COVID-19
Herpesvirus	DNA	Herpes infections
Bacteriophages	DNA	Infect bacteria

Multinucleated cells & very large cells

Multinucleated c. : contain multiple nuclei (z.b. skeletal muscle cells)

Very large c. : very large (z.b. nerve cells) → very long extensions

The scientists on cell theory, Letters?

H-S-S-V

Hooke → He named cells

Schleiden → studied plants

Schwann → studied animals

Virchow → vorherige cells create new cells

Why do cells must come from pre-existing cells?

Because they divide (mitosis) that’s how they reproduce

Why are cells mostly small (microscopic)?

Because exchange of materials become less efficient as cells increases

Surface Area-to-Volume Ratio (SA:V):

Small cell has larger surface area compared with its volume

Diffusion more efficient and faster!

Cells are measured in?

Micrometers µm

1 µm = 0,001 mm

Most cells are between: 1-100 μm

Examples of cell size: bacteria, mitochondria, human red blood cell, typical animal cell, human egg cell

Examples of Cell Sizes

Structure	Approximate size
Bacteria	1–5 µm
Mitochondria	0.5–1 µm
Human red blood cell	~7–8 µm
Typical animal cell	10–30 µm
Human egg cell	~100 µm

Neurons very long but cell body small!

What is diffusion?

Most substances move through cells by diffusion

is the movement of molecules from:

high concentration→ low concentration

(z.B. oxygen moves from blood into cells)

Efficiency of cell diffusions

The efficiency of diffusion is dependent on cell size! Small cell → good surface area compared→ efficient diffusion

How do cells solve the size problem? (name 3)

1. remaining small (not growing indefinitely)

2. changing shape (develop shapes that increase surface area, z.B. Red blood cells: small, flat, biconcave)

3. developing internal transport systems (blood vessels, circulatory systems)

The volume of a cell determines how quickly substances enter, why is this false?

Because volume alone is not argumentative enough!

It depends on the surface area to volume ratio, both needs to be included!

Procaryotic cells

no nucleus

DNA is not surrounded by membrane

main examples: bacteria, archaea

Structures:

1 cell membrane: controls movement of substances in and out the cell

2 cytoplasm: jelly-like substance with chemical reactions (holds cell together?)

3 DNA region (nucleoid): where DNA is circular and single chromosome

4 ribosomes: protein synthesis (70S ribosomes)

5 cell wall: outside of the membrane for protection & maintaining shape, contains peptidoglycan

6 flagellum (in some bacteria): for movement

7 capsule (in some bacteria): protective outer layer

usually smaller than eukaryotic cells

reproduce by binary fission

Eukaryotic cells

with nucleus

mebrane-bound organelles

examples: animals, plants, fungi, protists

Structures:

1 Nucleus: stores DNA (organized into chromosomes), controls cell activities

2 membrane-bound organelles: structures that perform specific functions: mitochondria, endoplas. Ret., Golgi ap., lysosomes

3 ribosomes: protein synthesis (80S ribosomes)

Main Differences Between Prokaryotic and Eukaryotic Cells

Main Differences Between Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic	Eukaryotic
Nucleus	❌ No	✅ Yes
DNA	Circular	Linear chromosomes
Membrane-bound organelles	❌ No	✅ Yes
Size	Smaller	Larger
Ribosomes	70S	80S
Cell division	Binary fission	Mitosis/meiosis
Examples	Bacteria	Animals, plants, fungi

Endosymbiotic Theory

some organelles originated from ancient bacteria that where engulfed by another cell.

Evidence: mitochondria and chloroplasts: have own circular dna, own ribosomes, double membrane, can divide

Similarities between prokaryotic and eukaryotic cells

1 cell membrane

2 cytoplasm

3 dna

4 ribosomes

Are mitochondria only found in animal cells?

No, plant cells also contain mitochondria

Difference between 70S & 80S ribosomes

70S ribosomes: in prokaryotes → smaller ribosomes in eukaryotic organelles

80S ribosomes: in eukaryotes → larger ribosomes in cytoplasm

S stands for Svedberg units (measure of how fast particles settle during a centrifuge spin → reflects size and density)

What have animal and plant cells in common?

Both eukaryotic cells with: nucleus, membrane-bound organelles (z.B. mitochondria for ATP through cellular respiration), 80S ribosomes, linear chromosomes

What additional structures do plant cells have?

• perform photosynthesis (chloroplasts)

• Maintain their shape (cell wall)

• Store water (large central vacuole)

Eukaryotic plant cell structures:

1Cell wall

2Chloroplasts

3Large central vacuole

Definition, function, reason

1Cell Wall:

Definition: rigid layer outside the cell membrane (out of cellulose)

Function: support, maintains structure, no bursting when water enters

Reason: through osmosis (water intake) cell could not hold water or cell swells and ruptures

2Chloroplasts:

Definition: organelles in plant cells for photosynthesis including Chlorophyll (green pigment, absorbs light energy)

Function and reason: light energy→ chemical energy (glucose)

Have their own dna, ribosomes, double membrane,

3Large central vacuole

Definition: large membrane-bound space filled with cell sap

Function: stores water, stores ions & nutrients, maintains pressure in cell (turgor pressure)

Eukaryotic animal cell structures?

(Name

1Centrioles:

Function: help organize microtubules during: cell division, formation of mitotic spindle

2Lysosomes:

Function: contain digestive enzymes, which break down: waste materials, old organelles, foreign substances

Plant Cells vs Animal Cells

Feature	Plant Cell	Animal Cell
Nucleus	✅	✅
Cell membrane	✅	✅
Mitochondria	✅	✅
Ribosomes	✅	✅
Cell wall	✅	❌
Chloroplasts	✅	❌
Large central vacuole	✅	❌
Centrioles	Usually absent	Usually present
Shape	More fixed	More flexible

Why do plant cells need to do photosynthesis?

Because plants can’t move to get food

They need chloroplasts to produce glucose with light through photosynthesis

Plants vs. Animal cells

Structure	Function	Found in
Cell wall	Support and protection	Plants
Chloroplast	Photosynthesis	Plants
Vacuole	Storage and pressure	Plants (large)
Centrioles	Cell division	Mainly animals
Lysosomes	Digestion/recycling	Mainly animals
Mitochondria	ATP production	Both

Membrane transport of cells

Transport	ATP needed?	Direction
Simple diffusion	❌	High → Low
Facilitated diffusion	❌	High → Low
Osmosis	❌	Water movement
Active transport	✅	Low → High
Endocytosis	✅	Into cell
Exocytosis	✅	Out of cell

Main roles of cell membrane

Controls what enters and leaves the cells

Allows communication between cells

Maintains internal environment of cell

What is the biology word for the description that the cell membrane lets some substances pass through and others don’t?

Selective Permeability