Module 1

What is the purpose of lipids in the phospholipid bilayer?

creating a hydrophobic barrier between inside and outside the cell

What is the purpose of the proteins within the phospholipid bilayer?

Mediating transport, facilitating structure-function relationships (e.g. connecting to the extracellular matrix)

What is the basic path from DNA to protein?

DNA → pre-mRNA → mRNA → mRNA → protein

Examples of endgoals of post-translational targeting

mitochondria, chloroplasts, peroxisome, nucleus

Examples of endgoals of co-translational targeting

Golgi, cell membrane/secretion, lysosomes, vacuoles, storage vesicles

Where are the eukaryote’s genetic instructions held?

the nucleus

What proteins organize DNA?

histones

What surrounds the nucleus of a eukaryote?

A double bilayer (nuclear envelope) perforated with pores large enough to let macromolecules in and out

What gives the nucleus its shape?

a protein network called the nuclear lamina

What is the nucleolus of a cell?

Located inside the nucleus, produces the ribosomes needed for protein synthesis

What is chromatin?

The combination of DNA strands and histone proteins

What are ribosomes?

RNA-protein complexes produced by the nucleus which work in the cytoplasm to translate nuclear-encoded mRNA or in chloroplasts/mitochondria to produce the proteins encoded in those genomes

What two locations can ribosomes be found in?

Free-floating in the cytoplasm or bound to the ER

What organelles are contained in the endomembrane system?

ER, golgi, cell membrane/secretion, lysosomes, vacuoles, storage vesicles, nuclear envelope

What is the term for the first layer of the golgi apparatus?

cis golgi

What happens to molecules that go through the ER?

they make their way through layers, each of which have different enzymes that modify their structure

What is the ER?

A normally smooth surface (smooth ER), but if it is active in protein synthesis, ribosomes associate with the membrane, giving it a rough appearance (rough ER)

How do the ER’s products leave it?

Via vesicles

What do the smooth ER’s enzymes mostly do?

lipid synthesis and detoxification

Why is the ER important in signalling?

It is a major intracellular store of calcium, particularly in muscular cells

If a cell’s main purpose is protein synthesis and secretion, what will there be an abundance of?

Rough ER

What is the golgi apparatus?

Processes vesicles and determines where their constituents should be directed

Steps of the golgi apparatus

1. Vesicles move from ER to Golgi

2. Vesicles coalesce to form new cis Golgi cisternae

3. Golgi cisternae move in a cis-to-trans direction to mature

4. Vesicles form and leave the golgi

5. Vesicles transport some proteins backward to less mature Golgi cisternae

Which side of the golgi faces the ER?

cis

What is PTM?

Post-translation modification

What is glycosylation?

adding monosaccharides to other molecules

Where does glycosylation occur?

endomembrane system

What can PTMs change?

• affinity for ligands

• catalytic activity

• stability

• targeting

What are lysosomes?

Produced by the golgi and contain enzymes that degrade macromolecules. Degrade material internalized by endocytosis and damaged intracellular products

What is autophagy?

the degradation of damaged or excess intracellular components by lysosomes

How do lysosomes “digest”?

They contain active hydrolytic enzymes. they fuse with the food vacuole and these enzymes digest the food particles

What are vacuoles?

Large vesicles separated from the cytoplasm and used primarily for storage. Most important in plants, where they store water, solutes, and nutrients

What is cytoplasm?

A viscous fluid with consistency between a liquid and gel. It is the solution in which ions, metabolites, and enzymes are dissolved, diffuse, and react

Describe the osmotic activity of cytoplasm

It is osmotically active, being diluted by movement of water into the cell and concentrated by loss of water. Total volume = cell volume

How is the chemical nature of cytoplasm controlled?

By transporters that move molecules in and out of the cell across the cell membrane

What is the cytoskeleton?

An internal protein framework that determines the shape of the cell and changes the shape as needed by adding and removing monomers

Where do motor proteins walk?

On the cytoskeleton

Virtually all forms of biological movement depend on what?

cytoskeletal proteins and molecular motors

What does myosin walk on?

actin microfilaments

What do dynein and kinesin walk on?

microtubules

Name the three main cytoskeletal polymers

microtubules, microfilaments, and intermediate filaments

Basic steps of evolution of eukaryotic cells

1. the use of membrane to separate genetic information from the cytoplasm

2. the acquisition of organelles via endosymbiosis

How does mitochondrial shape change?

Dynamically from single organelles to complex networks

What are chloroplasts?

Plastids that contain the pigment chlorophyl, an enzyme that permits photosynthesis by using light energy to produce carbohydrates

What are peroxisomes?

Organelles specialized to handle a subset of redox reactions, including those involving hydrogen peroxide. Cells protect themselves from damage by collecting the enzymes that produce and degrade hydrogen peroxide in this compartment

What are peroxisomes essential to produce?

ethanol, long fatty acid chains, uric acid, other toxic compounds

What is the extracellular matrix made of?

Fibres and mesh (collagen), gels (proteoglycan), crosslinkers (fibronectin), connections (integrins)

How is the ECM related to tumours?

When solid tumours metastasize, they secrete enzymes that break down the ECM

How do cells connect to one another?

Cells produce proteins to connect (cell junctions) which determine tissue integrity and restrict molecular movement between cells and within a membrane

What do tight cell junctions do?

Prevent things from passing through tissues between cells and restrict free movement of membrane proteins, which prevents proteins diffusing from end to end of the cell

What are the 7 properties of life?

1. Cellular organization

2. Reproduction

3. Growth and development

4. Metabolism

5. Homeostasis

6. Response to environment

7. Evolutionary adaptation

5 unifying themes of biology

1. organization

2. interactions

3. energy and matter

4. information

5. evolution

Define organization

Basic units of structure define the function of all living things

Define interactions

Living systems are interconnected and interacting

Define energy and matter

Biological systems grow and change based on chemical transformation pathways and are governed by the laws of thermodynamics

Define information

the growth and behaviour of organisms are activated through the expression of genetic information in context

Define evolution

The diversity of life evolved over time by processes of mutation, selection, and genetic change

What is the region of a bacterial cell that contains the genetic material?

The nucleoid

What are basal bodies?

structures at the base of cilia and flagella. They are derived from centrioles and serve as the anchoring and organizing centers from which cilia grow.

How is cilia/flagella movement generated?

By motor proteins

Where do proteins synthesized by free ribosomes go?

cytosol

Where do proteins synthesized by bound ribosomes go?

membranes, organelles, or secretion

Cell junctions in plant cells are called:

plasmodesmata

Communicating junctions in animal cells are called:

gap junctions

What kind of junction binds intestinal cells together?

Tight junctions

What are centrosomes made of?

centrioles

What are centrosomes?

animal cell organelles that serve to organize microtubules

Define amphipathic

Having both hydrophilic and hydrophobic regions

What is the fluid mosaic model?

Membranes are fluid (molecular movement) and mosaic (mixture of many types of molecules)

How is the cell membrane held together?

By hydrophobic interactions, which are weaker than covalent bonds

How often do adjacent phospholipids switch positions?

10⁷ times per second

Describe what happens to a cell membrane as temperature decreases

The membrane remains fluid as temperature decreases until a certain point, at which it solidifies. This point depends on the types of lipids it is made of

Under what circumstances would a membrane remain fluid to a lower temperature?

If it is rich in phospholipids with unsaturated hydrocarbon tails because they cannot pack as closely together

How does cholesterol affect membrane fluidity at high temperatures?

Makes the membrane less fluid by restraining phospholipid movement

How does cholesterol affect membrane fluidity at low temperatures?

Lowers the temperature required for the membrane to solidify

What are integral proteins?

Proteins that penetrate the hydrophobic interior of the lipid bilayer either partially or entirely (transmembrane)

What are peripheral proteins?

Proteins not embedded in the lipid bilayer and are loosely bound to the surface of the membrane

How are membrane proteins held in place?

By the cytoskeleton (inside) or extracellular matrix (outside)

Name some functions of membrane proteins

Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to cytoskeleton/ECM

How does HIV infect cells?

HIV binds to membrane proteins CD4 and the co-receptor CCR5 to enter immune cells. Some people lack CCR5 and are resistant.

What are membrane carbohydrates?

Usually short, branched chains of <15 units. They can be in the form of glycolipids or glycoproteins. they aid in cell-cell recognition

Steps for synthesis of membrane components

1. Membrane proteins are synthesized in association with the ER, and carbohydrates are then added to transmembrane proteins to create glycoproteins

2. Inside the Golgi, glycoproteins undergo further carb modification, and lipids acquire carbohydrates to form glycolipids

3. Glycoproteins, glycolipids, and secretory proteins are transported in vesicles to the plasma membrane

What type of molecules can cross the cell membrane w/o the aid of membrane proteins?

Nonpolar hydrophobic molecules like hydrocarbons, CO₂, and O₂

What types of molecules have difficulty passing through the cell membrane?

ions and polar molecules such as glucose, sugars, and water. Charged atoms/molecules and their surrounding water shells are even less likely to be able to penetrate

How do channel proteins function?

They have a hydrophilic channel that certain molecules or atomic ions use as a tunnel through the membrane

Example of a channel protein

Aquaporins allow entry of up to 3 billion water molecules per second passing single file through its central channel, which fits 10 at a time

How do carrier proteins work?

They bind to a ligand on the extracellular side and hold onto their passengers, change shape to shuttle them across the membrane

What does the selective permeability of a membrane depend on?

The discriminating barrier of the lipid bilayer and the specific transport proteins in the membrane

Define diffusion

the movement of particles of any substance so they spread out evenly

Simple rule of diffusion

In the absence of other forces, a substance will diffuse from where it is more concentrated to where it is less concentrated

What is passive transport?

The diffusion of a substance across a biological membrane without expending any energy, driven by electrochemical gradient

What is osmosis?

Osmosis is the movement of water across a selectively permeable membrane from an area of lower solute concentration to higher solute concentration until equilibrium is reached.

Define tonicity

The ability of a surrounding solution to cause a cell to gain or lose water

What is a hypotonic solution?

There is a lower solute outside the cell than inside → water enters the cell → the cell swells

What is an isotonic solution?

There is the exact same concentration of solute inside and outside the cell

What is a hypertonic solution?

There is a higher concentration of solute outside the cell → water leaves the cell → cell shrivels

Define osmoregulation

the process by which organisms control water and solute balance to maintain proper cell volume and internal conditions despite not living in an isotonic environment

define turgid

firm

What is plasmolysis?

When a shrivelling plant cell’s plasma membrane pulls away from the cell wall, causing the plant to wilt and die