Cells & Organelles

Mitochondria

• double layered organelle

• contains its own circular DNA & ribosomes

Mitochondria structures

1. Outer mitochondrial membrane - smooth

2. Intermembrane space - space btwn outer mmb and inner mmb

3. Inner mitochondrial membrane - folded numerous times to increase surface area (folding = cristae)

4. Mitochondrial matrix - space enclosed by inner mmb

Mitochondria - Functions

1. Synthesize ATP

2. Site of beta-oxidation (fatty acid catabolism/breakdown)

Chloroplast

• double membraned

• only present in cells capable of photosynthesis (e.g. plants, algae)

• contains its own circular DNA

• Derived from cyanobacteria

Chloroplast - Functions

1. Carry out photosynthesis (site of photosynthesis)

2. Gives plants their green appearance

• Absorbs red & blue light

• Reflects green light

Endosymbiotic Theory

• Mitochondria & chloroplasts part of eukaryotic cells; this is a theory that addresses the origin of these organelles

• States:

  • Mitochondria & chloroplast used to be independent prokaryotes

  • Formed a symbiotic relationship w/ a larger cell → eventually became organelles in eukaryotes

Endosymbiotic Theory - Evidence

1. Circular DNA - mitochondria & chloroplast have their own genome

2. Divide independently by binary fission (similar size to bacteria)

3. Contain other structures similar to bacteria

Animal cells vs Plant cells - Similarities

1. Eukaryotes

2. Have organelles in common (i.e. nucleus, smooth & rough ER, ribosomes, mitochondria, cell membrane, etc.)

Animal cells vs Plant cells - Key Differences

1. Plant cells have rigid cell walls, animal cells don’t have any cell wall

2. Animal cells more round in shape, plant cells are more square/rectangular

3. Animal cells have centrioles, plant cells do not

Organelles Unique to Plant Cells

1. Plastids - chloroplasts, leucoplasts, and chromoplasts

2. Storage Vacuoles - storage of starch, pigments, and toxic substances (like nicotine)

3. Cell Wall - found in plants, fungi, protists & bacteria

Leucoplasts

Stores nutrients

Chromoplasts

Stores plant pigments

Which of the following is true for both mitochondria & chloroplasts?

a) Both are single mmb organelles

b) Both are found in animal & plant cells

c) Both are derived from cyanobacteria

d) Both contain their own circular DNA

Both contain their own circular DNA

All of the following are found in plant cells but not animal cells EXCEPT one. Which one is the EXCEPTION?

a) Storage vacuoles

b) chromoplast

c) cell wall

d) mitochondria

e) chloroplast

Mitochondria

What are the two main wavelengths of light that chloroplasts absorb?

a) green & blue

b) green & red

c) blue & red

d) green & yellow

e) blue & yellow

Blue & red

Classes of Membrane Proteins

2 Classes - in terms of location

1. Peripheral membrane proteins

2. Integral membrane proteins

Peripheral Membrane Proteins

• loosely attached to one surface from the outside; not embedded into membrane

• mostly hydrophilic and/or held in place via H bonds & electrostatic interactions

How can you detach a peripheral protein from a membrane?

Change salt concentration or pH

Integral Membrane Protein

• embedded into the membrane itself

• only pass partially into membrane and stop at its interior

• mostly hydrophobic

Transmembrane Protein

A type of integral protein that goes all the way through the membrane on both sides

• Can connect the interior of the cell to exterior

• Allows substances to move in & out of cell

How can you remove an integral protein from a membrane?

Use detergent to destroy the membrane and expose the protein

Categorizing membrane proteins depending on function

1. Transport Proteins

2. Receptor Proteins

3. Glycoproteins

4. Enzymes

5. Adhesion/Anchor Proteins

Membrane protein - Transport proteins

• allow for movement of substances across the cell mmb (i.e. need transport protein to move glucose into cell)

(membrane proteins) Transport Proteins - Types

1. Channel proteins

• Ion channels

2. Carrier proteins

(transport protein) Channel Proteins

Hollow openings that allow substances to pass directly through

• Enables substances that normally wouldn’t be able to cross due to their size, shape, or charge to enter and exit cell

• Ex: aquaporins - let water molecules enter & exit cell much more quickly ; cell can regulate amount of water mvmt by changing how many aquaporins present in its mmb

• Ex: ion channels

(transport protein) channel protein - Ion Channels

Normally too charged to pass thru mmb on their own but w/ help of ion channels, can regulate mvmt in and out of cell

• can be regulated in diff ways

  • some are always open

  • others are voltage-gated: respond to differences in charges across mmb causes them to open or close

  • mechanically-gated: and close in response to pressure or temp or vibration

  • ligand-gated: signaling molecular binds and opens the channel

Especially important in nervous system

(transport protein) Carrier Proteins

Are transport proteins that allow for selective transport; work diff than channel proteins

• A specific molecule will bind to one side of carrier protein so it can pass across mmb → changes shape → repositions molecular in a way that allows it to pass to other side of mmb

• Ex: glucose

(membrane proteins) Receptor Proteins

Bind to signaling molecule then transmits changes to inside of the cell; binding site for hormones and other molecules

• Important in cell signaling & endocrine system

(membrane proteins) Glycoproteins

Protein molecules w/ carbohydrate group attached

Functions:

1. Cell-to-cell recognition

• Ex: immune cells: check mmb glycoproteins to identify that a cell belongs as part or organism or target for elimination if foreign cell

2. Cell signaling: (overlap w/ other mmb proteins) some glycoproteins can act as receptors by binding to signaling molecules

3. Cell adhesion: binding to molecules outside cell to help stabilize them

(membrane proteins) Enzymes

Help to accelerate chemical rxns by converting one substance to another

(membrane proteins) Adhesion/Anchor Proteins

Can be involved in attaching cells to adjacent cells to other proteins and filaments inside and outside cell for stability & cell communication

• Ex: junctions

Types of Junctions

1. Tight junctions

2. Anchoring junctions

3. Gap junctions

Tight Junctions

• Regulate selective movement of material btwn cells

• Form a seal btwn adjacent cells ensuring that there are no gaps or spaces to materials to pass in btwn them

• Means that materials must actually enter the cells directly in order to pass thru tissue

• Ex: digestive system’s digestive enzyme ; blood brain barrier

Anchoring Junctions

• Bind cells together and are important in structural cohesion of tissues

Gap Junctions

• Direct cell transfer of ions & small molecules (more like transport proteins)

• Connect adjacent cells together, role is not structural INSTEAD form narrow tunnels btwn cells that allow for effective cell-cell communication by allowing o passage of small molecules btwn adjacent cells

• Used for cellular activities like basic cell signaling, and conducting electrical signals

• Allow smooth synchronized electrical signal to spread thru tissue like heart (ions like Na+ can spread directly from one cardiac muscle cell to the next) → coordinated heart contraction

Adherens Junction

• Form a thick band that extends across cell and attaches them to adjacent cells helping to organize the cells into tissues

• ALSO attached to actin filaments on inside of cell to further stabilize

• Ex: cells that line blood vessels (for continuous connection for integrity)

Desmosome

• Similar to adherens junction

• Function: connect adjacent cells to each other but tend to be a much stronger connection

• Attached to intermediate filaments like keratin (inside of cell for reinforcement)

• Found in tissues exposed to lot of mechanical stress

  • Ex: cells & tissue of outer layer of skin and cardiac muscles - prevent them from being separated despite physical forces placed on them

Hemidesmosome

• Looks like half a desmosome, similar structure and are connected to intermediate filaments on the inside of cell HOWEVER, do not connect cells to adjacent cells INSTEAD attached cells to extracellular matrix (to a specific structure- basement mmb)

• Helps to stabilize cells and hold them in place preventing them from being detached from surface easily

• Found in tissues like epidermis of skin (outermost layer)

Cell Orientation

1. Apical surface - side of cell facing external environment or internal cavity (points outward, not attached to anything else) AKA outer surface or top side of cell

• Ex: skin cells facing outer environment

2. Lateral surface - sides of the cell

• Ex: touching cells adjacent to it

3. Basal surface - opposite the apical surface & bound to basement mmb, anchored to underlying connective tissue (bottom of the cell)

Basement Membrane

Structure that sits outside of cells, part of extracellular matrix that helps to anchor and support the cells attached to it

Which of the following membrane proteins are involved in cell-cell recognition?

a) anchor proteins

b) receptor proteins

c) transport proteins

d) glycoproteins

e) enzymes

Glycoproteins - function in cell reignition for immunity, where carb group can be used to identify a cell as self or non-self

Which type of membrane protein is embedded in the mmb and connects exterior to interior of the cell?

a) extracellular matrix

b) glycoprotein

c) peripheral protein

d) transmembrane protein

e) receptor protein

Transmembrane protein

ADH is a hormone responsible for the reabsorption of water, which type of membrane protein does it utilize?

a) ion channel

b) carrier protein

c) aquaporins

d) peripheral protein

e) enzymes

Aquaporins

Which of the following membrane proteins is always open?

a) voltage-gated

b) ligand-gated

c) mechanically gated

d) carrier proteins

e) channel proteins

Channel proteins

Glycoproteins play a role in all of the following EXCEPT one. Which one is the EXCEPTION?

a) cell-signaling

b) cell-cell recognition

c) immune system

d) cell-adhesion

e) cell mobility

Cell mobility

Which type of cell junction prevents the passage of substances between cells?

a) gap junctions

b) tight junctions

c) plasmodesmata

d) anchoring junctions

e) desmosomes

Tight junctions

All of the following, correctly match the location with the type of junction it primarily uses EXCEPT one. Which one is the EXCEPTION?

a) BBB and tight junctions

b) blood vessels and adherens junctions

c) cardiac muscle and gap junctions

d) epidermis of skin and tight junctions

e) digestive system and tight junctions

Epidermis of skin & tight junctions

Which part of cell is bound to basement membrane?

a) basal surface

b) apical surface

c) microvilli

d) lateral surface

e) extracellular matrix

Basal surface

Passive vs Active Transport - based on energy

• Passive: no energy is used to transport substances, passively move from one side of mmb to another (energetically favorable)

• Active: energy is required in form of ATP (moving against concentration gradient)

Transportation in Bio

When you build up a higher amount of substance on one side of a permeable mmb, and have lower amount of same substance on other side → concentration

• Cells want things to be balanced, difference in concentration of that substance => created biological imbalance that are energetically unfavorable → want to move from high conc to lower conc until balance is reestablished

Passive Transport

• Mvmt of substance across mmb w/ no expenditure of energy

1. simple diffusion

2. facilitated diffusion

Passive - Simple Diffusion

Net mvmt of substance down their concentration gradient directly thru cell mmb

• High conc → low conc

Passive - Facilitated Diffusion

Like simple diffusion BUT w/ assistance of a specific transmembrane transport protein

Active Transport

Mvmt of substance across cell mmb against concentration gradient

• Requires energy and specific transport proteins

1. Primary Active Transport

2. Secondary Active Transport

Primary Active Transport

Using ATP directly to move substance against its concentration gradient

Secondary Active Transport

Using an established electrochemical gradient to move a substance against its concentration gradient; does not use ATP