MLB 111 UNIT 1
Topic: Cells and Cell Structure (5 lectures)
STUDY MATERIAL: Hillis et al., Chapter 5
Lecturer: Dr Nicky Olivier
Core Concepts:
1.1 Cell Theory
1.2 Endomembrane structure
1.3 Cytoskeleton
LEARNING OUTCOMES:
You have mastered this study theme when you can:
1. Discuss the basic tenets of cell theory by explaining and applying the concept.
• cells are fundamental units of life
◦ life (therefore cells) has the ability to:
◦ reproduce
◦ respond to environment
◦ harness energy
◦ evolve
• all living organisms are composed of cells - unicellular e.g. bacteria, archaea, amoeba
etc; or multicellular e.g. mammals, plants etc.
• all cells from from preexisting cells (only way to get more cells is for existing cells to
divide - unbroken cell division line from modern cells to the first cells)
• modern cells evolved from a common ancestor
• Implications:
◦ cell biology is studying life
◦ life is continuous
◦ the origin of life is the origin of cells
2. Explain why most cells are so small by demonstrating the application of the surface area
to volume ratio and relating this to homeostasis. (p85)
"As an object increases in volume, the surface area also increases, but not at the same rate"
Important application is that larger cells' need for resources + waste production increase
faster than surface area. SA increases in proportion to r2 but volume increases in
proportion to r3 . (Volume increases faster). Thus large organisms must have many small
cells - maintain large surface area-to-volume ratio and ideal internal volume.
Cell shape can change as they become larger to maintain high ratio.
1
,Cell size is limited to maintain high surface area-to-volume ratio.
*Largest human cell is human egg, smallest is a sperm
Cells are small
Calculations of diameter vs surface area vs volume can make a ratio.
Can see that as cell gets bigger, volume gets much bigger than surface area. Can't get stuff
in or out fast enough bc SA doesn't increase fast enough.
Therefore as organisms problem is solved by having lots of small cells. Thus more efficient
(than big ineffective cells).
Another way to get around problem is:
• increased foldings of membranes
• increased size in one dimension (e.g. nerve cells become thin and elongated)
• increase rate of substance transport across membrane
But there is still a limit.
Water can get into cell either through membrane or proteins. Sometimes not enough
space for more proteins. Therefore limit to size.
Our cells are this size bc the ratio is ideal (able to survive).
3. Know four different functions of the cell membrane. (p86-87)
• Selectively permeable barrier - prevent some substances from crossing, permit others
to enter/leave. (e.g. water, gas)
• Maintain homeostasis - internal environment chemical reactions can occur away from
surrounding environment (regulated transport - maintain semi constant internal
environment). If not maintained the cell can stop functioning or die.
• Cell's boundary with outside environment - communication with adjacent
cells/receiving signals from environment
• Proteins can bind/adhere to adjacent cells i.e. structural role/shape of
cell/communication
(Rarely asked to just name functions. Rather asked to discuss in terms of something else like
lipid content or protein transport)
4. Explain the difference between cytoplasm and cytosol. (p87)
Cytoplasm: everything in the cell except nucleus
• Substances in cytoplasm always in motion. Ensures biochemical reactions proceed at
sufficient rates to meet needs of cell. A protein moves around entire cell within a
minute (very fast)
Cytosol: fluid not contained inside another compartment like a membrane or organelle
Important to distinguish difference bc different ribosomes are found in each and perform
separate functions.
5. Define the term "organelle" by using it in an appropriate manner in a discussion or short
question. (p87)
2
, Membrane-enclosed compartments in eukaryotic cells. Most notable is nucleus, ER, Golgi
apparatus etc.
Provides a compartment that separates molecules/biochemical reactions from the rest of
the cell. (Important bc compounds in organelles can perform purpose without disrupting
rest of cell, or if the concentration is lost in the cell the function can be less efficient)
Possibilities for regulation and efficiency.
6. Describe the characteristics of prokaryotic cells (Bacteria and Archaea) and know the
specialized features found in some prokaryotic cells. (88-90)
• No membrane-enclosed organelles (no nucleus).
• Generally smaller than eukaryotic cells: 1-10micrometers
• Cell membrane encloses cell - regulates traffic, separates internal from external
environment
• Nucleoid contains DNA - no separate compartment. Implication is that transcription
and translation is not separate. Processes aren't as well regulated.
• Rest of the material is in the cytoplasm
• Ribosomes - complexes of RNA and proteins in the cytoplasm, sites of protein
synthesis.
• Cell wall - support and shape. Outside cell membrane. Is a peptidoglycan cross-
linking (protein bound to carbohydrate). Makes the cell more hardy. Gram positive
bacteria has a cell membrane plus peptidoglycan layer. Some bacteria (usually gram
negative) has an outer membrane enclosing the peptidoglycan layer - permeable.
• Capsule - mostly polysaccharides outside cell wall. Protect cell wall from immune
system/from drying out/helps attachment to other bacteria.
• Internal membranes - Some contain molecules for photosynthesis (to produce
oxygen). Some are attached to cell membrane and function in cell division or energy-
releasing reactions
• Flagella - complex motor protein called flagellin (makes flagella) spins flagellum on
axis to drive cell (movement). Anchored to cell membrane or outer membrane of cell
wall. Function is movement.
• Pili - made of protein that projects from surfaces of some bacterial cells. Used for
adherence (to other bacteria or surfaces). Conjugative pili help bacteria exchange
genetic material. Shorter than flagella.
• Cytoskeleton - collective name for protein filaments playing roles in: cell division, cell
movement, maintaining cell shape. Homologous to eukaryotic cytoskeleton proteins.
7. Explain the importance of compartmentalization in eukaryotic cells. (p90)
Internal cell is isolated from external - regulation and efficiency (allows evolution and
increases complexity)
Compartmentalisation in a cell favours reactions inside that compartment (same reaction
may differ between two different organelles).
Organelle membranes separate charges for energy production (photosynthesis/respiration)
3
Topic: Cells and Cell Structure (5 lectures)
STUDY MATERIAL: Hillis et al., Chapter 5
Lecturer: Dr Nicky Olivier
Core Concepts:
1.1 Cell Theory
1.2 Endomembrane structure
1.3 Cytoskeleton
LEARNING OUTCOMES:
You have mastered this study theme when you can:
1. Discuss the basic tenets of cell theory by explaining and applying the concept.
• cells are fundamental units of life
◦ life (therefore cells) has the ability to:
◦ reproduce
◦ respond to environment
◦ harness energy
◦ evolve
• all living organisms are composed of cells - unicellular e.g. bacteria, archaea, amoeba
etc; or multicellular e.g. mammals, plants etc.
• all cells from from preexisting cells (only way to get more cells is for existing cells to
divide - unbroken cell division line from modern cells to the first cells)
• modern cells evolved from a common ancestor
• Implications:
◦ cell biology is studying life
◦ life is continuous
◦ the origin of life is the origin of cells
2. Explain why most cells are so small by demonstrating the application of the surface area
to volume ratio and relating this to homeostasis. (p85)
"As an object increases in volume, the surface area also increases, but not at the same rate"
Important application is that larger cells' need for resources + waste production increase
faster than surface area. SA increases in proportion to r2 but volume increases in
proportion to r3 . (Volume increases faster). Thus large organisms must have many small
cells - maintain large surface area-to-volume ratio and ideal internal volume.
Cell shape can change as they become larger to maintain high ratio.
1
,Cell size is limited to maintain high surface area-to-volume ratio.
*Largest human cell is human egg, smallest is a sperm
Cells are small
Calculations of diameter vs surface area vs volume can make a ratio.
Can see that as cell gets bigger, volume gets much bigger than surface area. Can't get stuff
in or out fast enough bc SA doesn't increase fast enough.
Therefore as organisms problem is solved by having lots of small cells. Thus more efficient
(than big ineffective cells).
Another way to get around problem is:
• increased foldings of membranes
• increased size in one dimension (e.g. nerve cells become thin and elongated)
• increase rate of substance transport across membrane
But there is still a limit.
Water can get into cell either through membrane or proteins. Sometimes not enough
space for more proteins. Therefore limit to size.
Our cells are this size bc the ratio is ideal (able to survive).
3. Know four different functions of the cell membrane. (p86-87)
• Selectively permeable barrier - prevent some substances from crossing, permit others
to enter/leave. (e.g. water, gas)
• Maintain homeostasis - internal environment chemical reactions can occur away from
surrounding environment (regulated transport - maintain semi constant internal
environment). If not maintained the cell can stop functioning or die.
• Cell's boundary with outside environment - communication with adjacent
cells/receiving signals from environment
• Proteins can bind/adhere to adjacent cells i.e. structural role/shape of
cell/communication
(Rarely asked to just name functions. Rather asked to discuss in terms of something else like
lipid content or protein transport)
4. Explain the difference between cytoplasm and cytosol. (p87)
Cytoplasm: everything in the cell except nucleus
• Substances in cytoplasm always in motion. Ensures biochemical reactions proceed at
sufficient rates to meet needs of cell. A protein moves around entire cell within a
minute (very fast)
Cytosol: fluid not contained inside another compartment like a membrane or organelle
Important to distinguish difference bc different ribosomes are found in each and perform
separate functions.
5. Define the term "organelle" by using it in an appropriate manner in a discussion or short
question. (p87)
2
, Membrane-enclosed compartments in eukaryotic cells. Most notable is nucleus, ER, Golgi
apparatus etc.
Provides a compartment that separates molecules/biochemical reactions from the rest of
the cell. (Important bc compounds in organelles can perform purpose without disrupting
rest of cell, or if the concentration is lost in the cell the function can be less efficient)
Possibilities for regulation and efficiency.
6. Describe the characteristics of prokaryotic cells (Bacteria and Archaea) and know the
specialized features found in some prokaryotic cells. (88-90)
• No membrane-enclosed organelles (no nucleus).
• Generally smaller than eukaryotic cells: 1-10micrometers
• Cell membrane encloses cell - regulates traffic, separates internal from external
environment
• Nucleoid contains DNA - no separate compartment. Implication is that transcription
and translation is not separate. Processes aren't as well regulated.
• Rest of the material is in the cytoplasm
• Ribosomes - complexes of RNA and proteins in the cytoplasm, sites of protein
synthesis.
• Cell wall - support and shape. Outside cell membrane. Is a peptidoglycan cross-
linking (protein bound to carbohydrate). Makes the cell more hardy. Gram positive
bacteria has a cell membrane plus peptidoglycan layer. Some bacteria (usually gram
negative) has an outer membrane enclosing the peptidoglycan layer - permeable.
• Capsule - mostly polysaccharides outside cell wall. Protect cell wall from immune
system/from drying out/helps attachment to other bacteria.
• Internal membranes - Some contain molecules for photosynthesis (to produce
oxygen). Some are attached to cell membrane and function in cell division or energy-
releasing reactions
• Flagella - complex motor protein called flagellin (makes flagella) spins flagellum on
axis to drive cell (movement). Anchored to cell membrane or outer membrane of cell
wall. Function is movement.
• Pili - made of protein that projects from surfaces of some bacterial cells. Used for
adherence (to other bacteria or surfaces). Conjugative pili help bacteria exchange
genetic material. Shorter than flagella.
• Cytoskeleton - collective name for protein filaments playing roles in: cell division, cell
movement, maintaining cell shape. Homologous to eukaryotic cytoskeleton proteins.
7. Explain the importance of compartmentalization in eukaryotic cells. (p90)
Internal cell is isolated from external - regulation and efficiency (allows evolution and
increases complexity)
Compartmentalisation in a cell favours reactions inside that compartment (same reaction
may differ between two different organelles).
Organelle membranes separate charges for energy production (photosynthesis/respiration)
3
