Cell Biology Flashcards
When was the cell discovered and by who?
Hooke (1665)
» Used a microscope to look at cork (ie tree bark)
» Saw little rooms, which he called “cellulae”
What is the cell theory and who invented it?
1830s - Schwann and Schleiden propose cell theory:
- The cell is the most basic unit of life
- All living organisms are composed of one or more cells
- All cells arise from pre-existing, living cells
Why are larger cells less common?
- Cells are very small (< 100 microns across)
- Large cells have less surface area per unit volume → less capable of transporting materials across the cell membrane
How do you work out the surface area of a cell?
Surface area (μm^2) (A = 4 π r^2)
How do you work out the volume of a cell?
Volume (μm^3)
V = 4/3 π r^3
What is the value of 1 micron?
1 micron = 1 μm
Some cells have evolved strategies to overcome issue of surface area:volume ratio, what are they?
» Low metabolic activity (eg, egg cells)
» Thin elongated cells (eg, giant squid neuron)
» Folds in membrane → increase surface area
What are the advantages of being a bigger organism? Why don’t we have more of them?
» Receive more sunlight
» Better defence against predators
- large cells are not efficient that’s why we have multicellular organisms
What does a light microscope do? What is its resolution
visible light is passed through the specimen and then through glass lenses. The lenses refract (bend) the light in such a way that the image of the specimen is magnified as it is projected into the eye or into a camera. Resolution = 0.2 μm
What is resolution?
a measure of the clarity of the image; it is the minimum distance two points can be separated and still be distinguished as two points.
What does an Electron Microscope do? What is its resolution?
focuses a beam of electrons through the specimen or onto its surface. Resolution = » Resolution ≈ 0.000 05 μm
All cells share four basic needs, what are they?
» Separate internal and external environments: plasma membrane (inside is jelly-like cytosol)
» Store information and pass it on to next generation (reproduce): DNA
» Read genetic code to build proteins: RNA and proteins (eg, ribosome)
» Conduct chemical processes of life: ingest food and energy, use it for metabolic activity and growth, and expel waste
- All cells do this, hinting at common ancestor
What are the three types of cells?
» Archae = “Prokaryotes”
» Bacteria = “Prokaryotes”
» Eukarya = “Eukaryotes”
What are Prokaryotes?
» Have DNA, ribosomes, and proteins enclosed in plasma membrane, but no internal separation
» Early life forms ≈ 4 BYA
What are Eukaryotes?
Eukaryotes have internal separation = “organelles”
» In particular, a nucleus which holds DNA
- Usually larger size (≈10× avg prokaryote)
- Appear later than prokaryotes (≈2.1 BYA)
How is DNA organised in a Eukaryote?
Eukaryotes have a double membrane (“nuclear envelope”) that
surrounds nucleus and protects DNA
» DNA is organised on many linear chromosomes
How is DNA organised in a Prokaryote?
Prokaryotes don’t have nucleus
» DNA is on one main circular chromosome
» Also numerous plasmids = small additional DNA
• Makes swapping DNA b/w prokaryotes much easier
(eg, antibiotic resistance)
Eukaryotes also evolved multicellularity, what does this mean?
» Collection of cells provide the benefits of larger size without exceeding size constraints of single cell
» Different cells needed to coordinate their activities
» Evolution refined coordination to the point where cells began to specialise in function
The lack of organelles in prokaryotes implies they have a different organisation, what does this mean?
» Prokaryotes have more metabolic options than eukaryotes
» Prokaryotes can survive in environments where eukaryotes cannot (reflection of their origin)
» There are more E. coli in the gut of a single human than there have ever been human beings on the planet
• Of 100 trillion cells in human body, 90% are bacteria
What is Emergence
Complex systems arise out of
multiple simple interactions
» Cells < organs (eg, brain)
» Organism < population (eg, termite mounds)
What is an organelle?
specialised membrane-bounded structure within a
living cell
» Remember: only eukaryotes have organelles (prokaryotes do not)
What is the nucleus?
Control centre of the cell
» Bound by double membrane (nuclear envelope)
» Encloses genetic material (DNA)
» Processes input from cytoplasm and carries out instructions on DNA (genes)
» Nuclear pores allow large
molecules (mRNA) to pass
What is the Nucleolus?
Dense centre of the nucleus where ribosomal RNA (rRNA) is synthesised
What is the Endoplasmic Reticulum?
Biosynthetic factory that is split into the rough ER and Smooth ER
