Unit Two: Cell Structure and Function

Cells are made of?

Biomolecules

After the invention of microscopes in the 1590s, what were discovered?

Cells were discovered and cell theory was soon(ishly) developed.

Robert Hooke 1665

Cells exist?

Anton Leeuwenhoek (1674)

Unicellular organisms exist!

Matthias Schleiden (1838)

Plants are made of cells! 

Theodor Schwann (1839)

Animals are made of cells!

Cell theory

• Every living organism is made of one or more cells.

• The cell is the structural and functional unit of all organisms, it is the smallest unit of life, individually alive even as part of a multicellular organism.

• All living cells arise by division of pre-existing cells.

• Cells contain hereditary material, which they pass to their offspring during division.

All prokaryotic cells are only made up of?

1. plasma membrane,

2. cytosol/cytoplasm,

3. genetic material (chromosomes), 

4. and ribosomes.

Pro

Before

Karyon

Kernel (nucleus)

What are the only types of prokaryotic cells?

Archaea and Bacteria

What is archaea more related to?

Eukarya

Archaea vs. Bacteria

What is on the outside of a prokaryotic cell?

Capsule 

Cell wall

Plasma membrane 

Pili

Flagella

Capsule

A sticky layer that helps prokaryotes stick to surfaces, some capsules add extra protection

Cell wall

Supports cell shape, protects cell, permeable to water (so dissolved stuff can cross into cell)

Plasma membrane

Plasma Membrane - Phospholipid bilayer

Pili

Some prokaryotes have these, they help the bacterium stick to surfaces. Other types of pili can be used to “spear and reel in” other bacteria to exchange plasmid DNA

Flagella

Used for motion, whips around like a propellor.

Ribosomes

Free floating, makes proteins

Plasmids

Small circular chunks of DNA, contains a couple of genes that are easily shared with other bacteria

Nucleoid

One large circular chunk of DNA. Contains rest of the bacteria’s genes. Not enclosed by a nucleus

Eukaryotic cells have internal membranes that 

• compartmentalize their functions (organelles), 

• isolate specialized environments (pH, molecules)

• and to increase internal surface area for reactions.

Eu

True

Karyon

Kernel (nucleus)

What are the two types of eukaryotic cells?

1. Autotrophic (plant-like)

2. Heterotrophic (animal-like)

Plant-like (autotrophic) cells include?

Plant cells and some protist/algal cells.

Animal-like (heterotrophic) cells include?

Animal cells, fungal cells, and some protist/protozoan cells.

Cell differentiation causes?

Cell structures/functions to vary among tissues and organs of multicellular organisms

:)

Endomembrane System

Efficiently coordinates the sending of proteins from ribosomes to their destinations.

Nucleus 

• Permanently stores DNA

• Hosts DNA synthesis (replication)

  • DNA contains directions to make proteins

Hosts RNA synthesis (transcription)

Nucleolus

Compartment of nucleus that makes ribosomes

Why do red blood cells do during development?

Kick out their nucleus (they enucleate) during development to make room for hemoglobin.

Chromatin

DNA and associated proteins in a cell nucleus

Nucleoplasm

Semifluid interior portion of the nucleus

Nuclear envelope

Double membrane with nuclear pores that control which substances enter and exit the nucleus 

Nucleolus

Dense region of proteins and nucleic acid where ribosomal subunits are being produced

Ribosomes are the site of?

Translation for protein synthesis. This is where proteins are assembled from amino acid monomers. 

Free ribosomes

Make cytoplasmic proteins

Bound ribosomes

Found on the rough E.R. and make membrane and excretory proteins.

Bound ribosomes are only found in?

Eukaryotic cells only. 

Free ribosomes vs membrane-bound ribosomes 

Endoplasmic Reticulum (ER)

Compartmentalizes the cell for protein synthesis, since it has bound ribosomes on its surface.

Proteins made by rough ER travel where?

Smooth ER to be packaged into vesicles and sent away to the golgi apparatus.

Other proteins stay in the smooth ER to become enzymes that break down macromolecules or poisons (detoxification).

The smooth ER makes what for the cell membrane?

Phospholipids

Golgi apparatus

Sort of like the “finishing” center of the cell.

They take vesicles delivered from the smooth ER and make final touches, like adding phosphate groups, etc. and then send the finished products to the cell membrane to be excreted out of the cell.

Where can vesciles also be sent to?

Lysosomes or peroxisomes.

Vesicles

Small membranous sacs that store materials or transport/secrete materials around/out of cells

Secretory vesicles

Use with the cell membrane to deliver membrane proteins or to release secretory proteins.

Through what process do secretory vesicles function?

Exocytosis

Vacuoles

Larger vesicles that function as storage for food, water, or waste.

Large central vacuoles

Found in plant cells.

Stores water and exerts an outward force (turgor pressure) on the cell wall to provide rigidity and structure to plants.

When plants wilt, they need water to replenish their large central

Contractile Vacuoles

In unicellular eukaryotes, like paramecium,  a contractile vacuole is used to dispel excess water.

It prevents the single-celled organism from absorbing too much water from its environment- which can cause the cell to die.

Lysosomes

Produced by the golgi apparatus. 

Digests old cell parts, large food molecules.

How do lysosomes digest?

By containing over 50 kinds of hydrolytic enzymes (enzymes that break chemical bonds). 

What is the role of lysosomes in white blood cells?

Destroy engulfed pathogens.

Lysosomes are only found in what type of cells?

Animal cells

Peroxisomes

Formed by fusing vesicles from the mitochondria AND the rough ER together. 

Where are peroxisomes mostly found in animals?

Liver

Where are peroxisomes mostly found in plants? Function?

Peroxisomes are found in greater numbers in seeds, and help break down the fats stored in seeds as the first energy source for the seed to germinate (sprout).

In what types of cells are peroxisomes found in?

Nearly ALL eukaryotes.

Mitochondria

Eukaryotic organelle that makes the energy molecule ATP through aerobic respiration (meaning oxygen is needed)

Cristae

Folds of the inner membrane

Why are cristae needed?

Inner membrane is folded because it needs more surface area to maximize the amount of chemical reactions occurring (more surface area=more ATP being made)

Matrix

The very innermost (light orange) area of the mitochondria

Matrix function

Stores enzymes, proteins, ribosomes, and mitochondrial DNA.

Mitochondrial DNA

Yes, the mitochondria has its own DNA!!! 

You inherit mitochondrial DNA from your maternal lineage.

Chloroplasts

Function in photosynthesis in plants and algae.

Contains the pigment chlorophyll

Clorophyll

Gives plants/protists green coloration

Chlorophyll captures energy from the sun and carbon from CO2 in the air to turn into glucose. 

Thylakoids

Flat green pancakes that store chlorophyll and collect sun energy for the first part of photosynthesis

Grana

Stacks of thylakoids

This is another way to increase surface area.

Stroma

Fluid that surrounds the thylakoids. It is the site where the second half of photosynthesis occurs.

It also contains ribosomes and chloroplast DNA.

Why do some organelles have their own DNA?!

Chloroplasts, other plastids, and mitochondria are theorized to be a part of eukaryotic cells by the Endosymbiotic Theory.

Endosymbiont theory

Suggests that a long time ago, a symbiotic relationship (mutualism, meaning both species benefit) formed between early eukaryotes and prokaryotes. 

Cytoskeleton

Network of structural proteins extending throughout the cytoplasm. 

An interconnected system of many protein filaments – some permanent, some temporary

Parts of the cytoskeleton do what?

Reinforce, organize, and move cell structures, or can even move the whole cell.

What are extensions of the cytoskeleton that allow for cell motility?

Cilia and flagella

Motor proteins

Can use the cytoskeleton as highways and drag important stuff around with it.

Centromeres

Animal cells have them (made of centrioles) to organize microtubules, especially during mitosis.

Is the cytoskeleton and internal or outside cell structure?

Internal!

Cell walls

Cross-linked networks of structural polysacchrides

Cellulose

Plant cell walls are made of this

Chitin

Fungal cell walls are made of this

Peptidoglycan

Some bacterial cell walls are made of this

Extracellular Matrix

Animal cells have an (ECM), networks of connective proteins (like collagen) outside the cell membrane.

Think of the ECM as an? Example?

External support scaffold and how cells can adhere together better.

Collagen defects cause tissues to “tear” very easily.

Cell Junctions

Proteins also connect cells through intercellular junctions, sometimes creating open channels.

Why Worry About Cell Size?

• Cells must exchange substances with its environment at a rate that keeps up with its metabolism.

• The cell membrane can only handle so many exchanges at a time.

What does a bigger cell surface allow for?

The bigger a cell’s surface area is, the more substances can cross the membrane at any given interval. 

Efficient transport in a cell requires

A surface area to volume ratio that is as high as possible.

Or, the centre of a larger cell will die as diffusion of compounds will take too long

As organisms increase in volume, what decreases?

Their surface area to volume ratio decreases. 

Basically, if a cell is getting bigger, its volume increases faster than its surface area.

Surface area is needed for transport!

😽

Cells are limited in size, how?

• Too large → cannot exchange matter efficiently (nutrients can’t travel inside the cell fast enough, or wastes can’t be transported out fast enough). 

• Too small → not enough materials can fit inside, or heat and nutrients diffuse out too fast to keep the cell alive.

Size Solution #1

Multicellular organisms maintain large volumes by increasing their surface area with many individual cells. Divide and conquer!

Size Solution #2.

Cell Shape:

Large cells that need more interaction with their environment will either stretch out, or form convolutions like microvilli to increase surface area.

Which organelles stretch out, or form convolutions like microvilli to increase surface area?

Chloroplasts, ER, Golgi Apparatus, and mitochondria do this too, as their function depends on chemical reactions occurring on cell membrane surfaces.

Examples of size solution #2.

Example 1- Small intestine is site of nutrient absorption. Microvilli and villi increase surface area to have more membrane to absorb more nutrients. 

Example 2- Cells like neurons and muscle cells that can be as long as an entire limb stretch out to increase surface area.

Life needs membranes to?

Separate the internal environment from the external environment and to compartmentalize metabolism. 

How many layers are there in a cell membrane?

Made of two layers of phospholipids.