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Cells

Cells: the basic structural and functional units of every organism

All cells:

Are bound by a plasma membrane
Contain cytosol
Contain chromosomes
Contain ribosomes

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Cells

There are two types of cells: prokaryotes and eukaryotes

Prokaryotes

Eukaryotes

Domains Bacteria and Archaea
DNA is in the nucleoid region
Generally smaller in size than eukaryotes

Protists, fungi, animals, and plants
DNA is in the nucleus
Contain membrane bound organelles

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Organelles

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Organelles

Organelles: membrane bound structures in eukaryotes

Two classifications:

Endomembrane organelles

Nuclear envelope
Endoplasmic reticulum
Golgi complex
Lysosomes
Vesicles/Vacuoles
Plasma membrane

Energy organelles

Mitochondria
Chloroplasts

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Compartmentalization

Compartmentalization in organelles allows for different metabolic reactions to occur in different locations – makes them more efficient!

Increases surface area for reactions to occur

Prevents interfering reactions from occuring in the same location

Topic 2.10

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Unique Cell Components

Plants

Animals

Chloroplasts
Central vacuole
Cell wall
Plasmodesmata

Lysosomes
Centrosomes – in nucleus
Flagella

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Endomembrane Organelles

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Nucleus

Contains chromosomes (genetic information)

Enclosed by the nuclear envelope

Double membrane

Has pores

Pores regulate entry and exit of materials from cell

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Nucleus

Contains a nucleolus

Dense region of the nucleus where ribosomal RNA (rRNA) is synthesized

rRNA is combined with proteins to form large and small subunits of ribosomes
Subunits exit via nuclear pores

Assemble into ribosomes

Ribosomes translate messages found on mRNA into the primary structure of polypeptides

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Review

In order for DNA to leave the nucleus, it must first be transcribed by RNA polymerase into messenger RNA (mRNA). The mRNA transcript must then be modified before leaving the nucleus to the cytoplasm.

In the cytoplasm, the ribosomes decode the information in mRNA and form continuous chains of amino acids, thus forming a protein. This process of DNA → RNA → protein is known as transcription and translation and will be the main concepts covered in Unit 6.

Answer questions 1-3.�

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Ribosomes

Comprised of ribosomal RNA and protein

Function: synthesize proteins

Note: some texts do not classify ribosomes as organelles because they are not bound by a membrane

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Ribosomes

Can be found in two locations:
Cytosol

Proteins produced here generally function only within the cytosol (i.e. enzymes)
Known as “free ribosomes”

Bound to endoplasmic reticulum or nuclear envelope

Proteins produced here can be secreted from the cell

Leave via transport vesicles

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Endoplasmic Reticulum

A network of membranous sacs and tubes

Functions:

Synthesizes membranes
Compartmentalize the cell to keep proteins formed in the rough ER separate from those of free ribosomes

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Endoplasmic Reticulum

Two types: rough and smooth

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Endoplasmic Reticulum

Rough ER

Contains ribosomes bound to the ER membrane

Smooth ER
Contains no ribosomes
Synthesizes lipids, metabolizes carbohydrates, and detoxifies the cell

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Golgi Complex

Contains flattened membranous sacs called cisternae

Separate the sacs from the cytosol
Each cisternae is not connected
Has directionality

Cis face:

Receives vesicles from the ER

Trans face:

Sends vesicles back out into cytosol to other locations or to the plasma membrane for secretion

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Golgi Complex

Functions:

Receives transport vesicles with materials from the ER
Modifies the materials
Sorts the materials
Adds molecular tags
Packages materials into new transport vesicles that exit the membrane via exocytosis

Ensures newly formed proteins are folded correctly or modified correctly

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Lysosomes

Membranous sac with hydrolytic enzymes

Function:

Hydrolyzes macromolecules in animal cells
Autophagy: lysosomes can recycle their own cell’s organic materials

Allows the cell to renew itself

Peroxisomes -Similar to lysosomes

Membrane bound metabolic compartments that break down toxic substances (like H₂O₂)

Catalyze reactions that produce H₂O₂

Enzymes in peroxisomes then break down H₂O₂ to water CLIP

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Vacuoles

Large vesicles that stem from the ER and Golgi

Selective in transport

Types:

Food vacuole

Form via phagocytosis (cell eating) and then are digested by lysosomes

Contractile vacuole – like a pump

Maintain water levels in cells

Central vacuole

Found in plants

Contains inorganic ions and water
Important for turgor pressure

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Practice FRQ

Hepatitis C is a virus that attacks the liver and can cause liver disease. Liver disease has been linked to a reduction in albumin levels in patients analyzed. Albumin is an important protein in humans. It functions primarily to regulate oncotic pressure of blood, which is important for the regulation of fluids in vessels of the body and tissue repair.

On average, patients with liver disease show a 10-30% decrease in blood-albumin levels.

Identify the organelle in liver cells that is most likely being affected by hepatitis C
Justify your reasoning.

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Practice FRQ

In humans, pancreatic cells synthesize the protein insulin in the endoplasmic reticulum (ER). Patients diagnosed with type 1 diabetes have immune systems that mistakenly attack their pancreatic cells. Therefore, these patients cannot produce the hormone insulin and have to take medications to introduce insulin into their bodies

(a) Describe how insulin would be produced in a normal functioning (non-type 1 diabetes) pancreatic cell.

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Energy Organelles

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Endosymbiont Theory clip

Endosymbiont Theory: the theory that explains the similarities mitochondria and chloroplasts have to a prokaryote

Theory states that an early eukaryotic cell engulfed a prokaryotic cell

Prokaryotic cell became an endosymbiont (cell that lives in another cell)

Became one functional organism

Endo vs Exocytosis clip

Topic 2.11

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Endosymbiont Theory

Evidence:
Double membrane
Ribosomes
Circular DNA
Capable of functioning on their own

Topic 2.11

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Mitochondria

Site of cellular respiration

Structure of the double membrane:

Outer membrane is smooth
Inner membrane has folds called cristae

Divides the mitochondria into two internal compartments and increases the surface area

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Mitochondria

Intermembrane: space between inner and outer membrane
Mitochondrial matrix: enclosed by inner membrane – matrix is fluid

Location for the Krebs cycle
Contains:

Enzymes that catalyze cellular respiration and produce ATP
Mitochondrial DNA
Ribosomes

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Mitochondria

The number of mitochondria in a cell correlates with metabolic activity

Cells with high metabolic activity have more mitochondria

Example: cells that move/contract

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Chloroplast

Specialized organelles in photosynthetic organisms

Site of photosynthesis
Contains the green pigment chlorophyll

Inside of its double membrane:

Thylakoids

Membranous sacs that can organize into stacks called grana

Light dependent reactions occur in grana

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Chloroplast

Stroma: fluid around thylakoids

Location for the Calvin cycle
Contains

Chloroplast DNA
Ribosomes
Enzymes

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The Cytoskeleton

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Cytoskeleton

A network of fibers throughout the cytoplasm

Give structural support (especially for animal cells) and mechanical support:

Anchor organelles
Allow for movement of vesicles and organelles and/or the whole cell

Movement occurs when the cytoskeleton interacts with motor proteins – these aid in cell division, muscle movement, etc

How vesicles inside cell move around

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Cytoskeleton

There are 3 types of fibers in the cytoskeleton:

Microtubules
Microfilaments
Intermediate filaments

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Microtubules

Hollow rod-like structures made of the protein tubulin

Grow from the centrosome

Assist in microtubule assembly

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Microtubules

Functions:

Serve as structural support (think: tracks) for the movement of organelles that are interacting with motor proteins

Assist in the separation of chromosomes during cell division

Cell motility (i.e., cilia and flagella)

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Microfilaments

Thin solid rods made of the protein actin

Functions:

Maintain cell shape

Bear or hold tension

Assist in muscle contraction and cell motility

Actin works with another protein called myosin to cause a contraction

Division of animal cells

Contractile ring of the cleavage furrow

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Intermediate Filaments

Fibrous proteins made up of varying subunits
Permanent structural elements of cells

Functions:

Maintain cell shape
Anchor nucleus and organelles
Form the nuclear lamina

Lines the nuclear envelope & anchors nuclear pores in place

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Practice FRQ

You are working in a research lab and your goal is to determine the effect that alcohol has on the liver. You design an experiment where you expose samples of liver tissues to varying concentrations of alcohol as follows:

Sample	Concentration of alcohol	Duration of exposure
Sample 1	0.25 mg/mL	20 minutes
Sample 2	0.35 mg/mL	20 minutes
Sample 3	0.45 mg/mL	20 minutes

After exposure to the alcohol, you analyze the liver samples. In all samples you find that the alcohol has been broken down (detoxified). However, in sample 3 you find damage to organelles has occured due to the high concentration of alcohol. (a) Identify one organelle in the liver that could be responsible for the detoxification of the alcohol in all three samples. (b) In sample 3 identify the organelle that would most likely be responsible for removing the damaged parts of organelles and (c) describe the steps it would take to do so.