Lecture 01: Intro to Cell Biology

What is Cell Biology?

• All living organisms are composed of cells

• Cells are the fundamental unit of life.

• “The key to every biological problem must finally be sought in the cell; for every living organism is, or at some time has been, a cell” – E.B. Wilson

What is Brownian motion?

• random movement of particles caused by their constant collisions with surrounding molecules.

• In cells, it drives diffusion, influences the rate of biological reactions, and contributes to the movement of molecules within the cell.

• Cells can harness Brownian motion to help generate directed movement, such as during cell migration.

Robert Hooke (1665)

Examined cork under microscope - made up of “cells”

Anton van Leeuwenhoek (1674)

Examined pond water under microscope -“animalcules” (Microscopic organisms)

Matthias Schleiden (1838), Theodor Schwann (1839) & Rudolf Virchow (1855) proposed the 

Cell Theory

Cell Theory

1. All organisms are composed of one or more cells.

2. The cell is the structural unit of life.

3. Cells can arise only by division from a preexisting cell (Not spontaneous like previously thought)

Cell biology is the study of cells at microscopic and molecular levels.

• Properties of cells

• Organelle structure

• Interactions between cells

• Cell movement

• Movements of macromolecules between organelles

• Specialized cells (skin cells not the same as neurons, but specified for each function)

• Basic cell/molecular biology can pave the way for important medical advances

Universal Features of Cells

• Cells store information in double stranded DNA.

• Cells can  replicate their DNA

• Cells can transcribe portions of their DNA into RNA, Cells can translate RNA into proteins, Each protein is encoded by a specific gene.

• Cells can make more of themselves (multiple terms: replicate, divide, multiply)

• Cells can acquire and use energy (e.g. metabolic reactions)

• Cells can use proteins as catalysts

• All cells have a  plasma membrane

• Made of phospholipids

• Cells have constant movement

DNA and RNA is made of

Nucleotides

Amino acids make up

proteins

Cells store information in double stranded DNA.

• Nucleotides come together to give use a single nucleotide strand

• But DNA needs 2 strands, so template used to make a new DNA strand

• A base pair with T, and C base pair with G

• Sequence of nucleotides determines at what time and how much is gene going to be expressed

Is RNA double or single stranded

Single

Nucleotide made of

Sugar (deoxyribose), phosphate and nitrogenous base

4 nucleotides for DNA

• A, G, T, C

• In RNA there is U instead of T

Differences in DNA and RNA

• the sugar in their backbone (deoxyribose in DNA vs. ribose in RNA)

• the bases they contain (thymine in DNA, uracil in RNA),

• their structure (double-helix vs. single-strand)

Cells can  replicate their DNA

• Cells can replicate their DNA.

• During replication, the parental double helix separates into two single strands. Each strand serves as a template for building a new complementary strand.

• This ensures that when a cell divides, each daughter cell receives a complete copy of the DNA.

Cells transcribe DNA to RNA, Translate RNA to protein, protein encoded to specific gene

DNA → RNA called

Transcription

RNA → proteins called

Translation

Sequence of amino acids in protein is determined by

RNA. That sequence is determined by the DNA.

Cells can acquire and use energy and catalysts

• Without energy cell can’t accomplish much

• Energy powers entire multicellular organism

• Cells take food in → use energy to make building blocks → use energy for work → waste is discarded out of cell

Not all proteins have catalytic activity.

• Some serve structural, transport, or regulatory functions.

• Example: Chaperones help other proteins fold correctly, rather than catalyzing reactions.

All cells have a plasma membrane

Catalyst

molecules that speed up a chemical reaction without changing

Plasma membrane

• selective barrier – allows the cell to concentrate nutrients from the environment, synthesize new products and excrete waste products.

• Fluid model not rigid structure

Membranes made of

Phospholipids

Phospholipids

• hydrophilic head, hydrophobic tails

• Molecule itself is amphiphilic (attracted to both hydrophobic and hydrophilic molecules)

Phospholipids in water form

• bilayers that form closed vesicles

• Phospholipids are amphiphilic (hydrophilic head + hydrophobic tails).

• In water, they spontaneously congregate so that the hydrophobic tails avoid water and the hydrophilic heads face it.

Cells have constant movement

• Individual components can self-assemble and become highly organized

• Constant movement of material within the cell → Brownian motion, energy (ATP) driven movements etc.

Can whole cells move

Yes

Brownian motion: 

• Random movement of particles →derives diffusion → can determine rate of biological reactions because reactions are based on concentrations (concentrates can vary in different areas of cell, stopping or starting certain reactions)

• Cells can harness Brownian motion for movement

• E.g. Actin filaments (cytoskeleton of cell) can act as ratchets to prevent membrane from moving back to its original position.

• In a migrating cell, this drives protrusion of the membrane → contributes to forward movement of cells

Cells Obtain free energy in different ways:

• Phototrophic

• Lithographic

• Organotrophic

Some cells specialize in fixing nitrogen and carbon dioxide (CO2) 

• other cells and organisms rely on these important processes

• Plants fix CO2

• Nitrogen-fixing bacteria help plants fix N2

Phototrophic 

Rely on sunlight

Lithotrophic 

inorganic chemicals in environment

Organotrophic 

other living things and the organic chemicals they produce

Three major domains

Eukaryotes, Bacteria, and Archaea

Organisms or bacteria found How deep in the Earth

10-11km

Is stuff alive in the atmosphere

• Yes, for example Breathing bacteria, hair

• 60-70 km in the air

Eukaryotes

make up the domain of life that is most familiar to us.

Bacteria

are the most diverse group of organisms on the planet.

Archaea

considered the most mysterious domain of life because they live in extreme environments and sometimes we don’t know what to look for (look like bacteria and eukaryotic genome)

How do we tell the difference in different bacteria’s or single celled species we can’t see

We start looking at their DNA and protein sequences

Types of cells

• Prokaryotes

• Eukaryotes

Prokaryotes: 

• Single-celled microorganisms that lack a membrane-enclosed nucleus (or other membrane bound organelles).

• Pro = before

• Karyon = nucleus

Types of prokaryotes:

• Bacteria (eubacteria) → true bacteria

• Archea (archaebacteria)

Archea (archaebacteria)

structurally similar to bacteria, but genome is closer to eukaryotes

Eukaryotes: 

• Organisms made up of one or more cells that have a distinct membrane bound nucleus

• Eu = True

• Karyon = nucleus

• Contain organelles →discreet membrane bound sub-compartments (e.g. mitochondria, endoplasmic reticulum (ER), Golgi apparatus and other membrane bound vesicles and organelles.

• Much larger and more complex than prokaryotes (1000-10000X larger in volume)

• Fungi, protists, plants, animals etc.

T or F, Eukaryotes can be unicellular or multicellular and may have organelles with no membranes!

True for example Centrosomes are not membrane bound

Ex of eukaryotes

Plant vs animal cell

What do plants have that animal cells don’t

• Chloroplasts (stroma, thylakoids, outer and inner membrane) → photosynthetic reactions happen

• Cell wall

• Large central vacuoles

• Plasmadesmata

What do animals have that plant cells don’t

• Lysosomes

• Centrioles

• Flagella

Did Eukaryotes Arise from Prokaryotes?

Eukaryotes may have arisen by a merger of two cells →  Endosymbiont Theory

Endosymbiont Theory

• explains that key eukaryotic organelles, like mitochondria and chloroplasts, originated from free-living prokaryotic cells that were engulfed and established a symbiotic relationship within a host cell

• Combination of two cells living in a symbiotic relationship where one cell lives inside the other

Mitochondria may have evolved from a

• symbiotic aerobic bacterium captured by an ancient archaeon

• Size of mitochondria is similiar to size of bacteria

Chloroplasts may have evolved from

• a symbiotic photosynthetic bacterium engulfed by an ancient eukaryotic cell

• Early evidence we have is of bacteria, so we think they cam first

T or F Eukaryotes don’t have hybrid genomes

F, Eukaryotes have Hybrid Genomes

Hybrid genomes

genetic information originated from an ancestral archaeon and endosymbiotic bacteria

Eukaryotic genomes are big  

rich in regulatory DNA

Eukaryotes can form Multicellular Organisms

• Most eukaryotes are unicellular organisms →even at this level, they can be fairly complex and, in some cases, behave like multicellular organisms.

• Differentiated cells express cell-specific genes  → gives rise to cell specific proteins → determine the cell function→ multicellular organism.

• Transcription regulators will only be around genes they need. In muscle cell, gene 1 is silenced. In skin cell gene 3 is silenced

Multicellular organisms are made up of a

• group of cells that perform specialized functions

• linked through complex cell-to-cell communication

• different groups of cells make up the organism.

• But…they all arise from a single cell!

Differentiation:  

• The process by which an unspecialized cell becomes specialized

• highly complex and regulated process where the genome / genes define the program of multicellular development

• Stem cell gets differentiated more and more as it divides

Differentiation occurs mostly through signals received from the cellular environment:

• Changes in cell morphology (appearance)

• “Housekeeping” genes (e.g. cell metabolism) will be the same as others

• Organelles stay the same, but their number and location may differ

Multicellular Organisms Start

• as Single Cells

• Ex development of a frog