Cell Structures and Functions

Cells 2

Honors BiologyMilton High School

Eukaryotic organelles

“Specialists” because they have their own membrane, unique proteins inside

Organelles can control internal environment, enzyme activity to do a particular job for cell

Ex: lysosome – breaks down food, invaders, old proteins

Recall that most cell processes involve chains of enzymes

Organelles pack enzymes together so reactions happen efficiently

Organelles only found in eukaryotic cells … perhaps allowed cells to become larger over time

ONLY eukaryotic cells have potential to be multicellular (no truly multicellular bacteria)

Why have organelles?

Two major groups of workers:

1) Protein production◦ endoplasmic reticulum◦ Golgi apparatus◦ (also, vesicles and the cytoskeleton)

2) Energy transformation◦ mitochondrion◦ chloroplast

3) Also the vacuole and lysosome

Our organelle discussion

Recall – where is code for building proteins?

Recall – what structure assembles proteins?

For prokaryotic cells, end of story (protein is built and ready to go)

For eukaryotic cells, protein is often modified by organelles

Protein production and shipping

Eukaryotic protein producers

(endoplasmicreticulum)

DNA

ribosome(little red dot)

Eukaryotic protein productionDNA

ribosome

code is copied, sent to

endoplasmic reticulum

puts together amino acids, gives to

Golgi apparatus

more about this in genetics (ch. 16)

modification of protein

final destination

final modifications, tagged for shipping

Eukaryotic protein producers

(endoplasmicreticulum)

DNA

ribosome(little red dot)

Cells are NOT just bowls of jelly

Proteins travel along cytoskeleton “roads”

Carried inside a vesicle (piece of membrane) by a motor protein

Getting from place to place

Depends on the protein

1. Cytoplasm

2. Cell membrane

3. Organelle membrane

4. Inside organelle

5. Secreted outside cell

What is the “final destination”?

Mitochondrion – converts food energy into ATP energy

Chloroplast – converts sunlight energy into food energy

Energy transformation in cells

= cell respiration

= photosynthesis

By the way, prokaryotes can still do both, they just use their cell membrane

Vacuole – storage (food, water, other compounds)

(especially large in plant cells)

Lysosome – breakdown (lyse = breaking up) – can be pathogens, food, old proteins (recycling amino acids)

Other organelles

We’ll compare plant vs. animal, eventually we’ll look at protist, fungi cells also

Comparing eukaryotic cells

plant cell animal cell

large central vacuole

chloroplasts

cell wall

Cell wall – structural support for cell

NOT the same as a cell membrane

ALL cells have a cell membrane

SOME cells have a cell wall (NOT animals)

Cell wall (vs. cell membrane)

There is no such thing as a “typical” animal / plant cell

Cells are very diverse in shape / function around an organism

And by the way

We’ve discussed membranes broadly

Our goal now:

◦ how a membrane is built to do its job,

◦ how particles move in and out of cells,

◦ how a membrane helps to maintain homeostasis

Membranes in more detail

2 major components of a membrane

1) Phospholipid bilayer (purple)

2) Proteins (blue)

Real membranes are liquidy (not motionless)

Membrane structure

Polarity leads to self-assembly in a bilayer

Water on both sides attracts polar heads, repels nonpolar tails

Component 1: phospholipids

Polar head

Nonpolar tails

Polar heads

Polar heads

Nonpolar tails

Polar water inside cell

Polar water outside cell

Purpose of bilayer: block most particles from getting through

Effectively blocks polar particles

Small, nonpolar molecules can still cross (ex: O2, CO2)

Component 1: phospholipids

Polar heads

Polar heads

Nonpolar tails

Polar water inside cell

Polar water outside cell

First, we’ll focus on transport proteins

Like enzymes, have specific shape to let specific particle pass through membrane

Component 2: proteins

Phospholipid bilayer blocks almost all particles from entering or leaving

Multiple types of transport proteins select what particles cross

= membrane’s ability to control movement

Overall membrane

Enzymes

Receptor proteins – receive signals from outside, pass along message

Marker proteins – identify type of cell

Other membrane protein types

Before discussing movement around membranes, let’s discuss particle movement more broadly

Individual particles move randomly, though the overall group moves very predictably

Particles ALWAYS spread out, or move from high concentration toward low concentration

Particle movement

Natural movement is for particles to move from high low concentration

Each particle type can be considered independently

Particle movement and membranes

Random movement continues, but eventually no net change because particles already spread out = dynamic equilibrium

This assumes particles can cross membrane … if not, then no change occurs

Particle movement and membranes

If cell allows particles to move naturally, = passive transport

Different types of passive transport depending on how particle gets through membrane

1. Diffusion2. Facilitated diffusion3. Osmosis

Particle movement and membranes

Particle can cross directly through phospholipid bilayer

Small, nonpolar molecules (O2, CO2)

Diffusion

Particle can only move through a transport protein (polar particle)

Osmosis is the facilitated diffusion of water specifically

Facilitated diffusion

Even if particles cannot move across membranes, they influence the movement of water

Any particle dissolved in watery solution = solute

Overall solute level influences water movement

Key: water follows the solute

Water movement

Water follows the solute

Water movement

Hypotonic – solute level is lower

Hypertonic – solute level is higher

Isotonic – solute level is equal

Water movement terms

Water follows the solute

Water movement

Inside: hypertonicOutside: hypotonic

Inside: hypotonicOutside: hypertonic

Inside: isotonicOutside: isotonic

Animalcell

Hypotonic environment

Isotonic environment

Hypertonic environment

Plantcell

Always movement from high low concentration

Always leads to equilibrium (equal concentrations inside and outside cell)

Often, cells do NOT want this equilibrium – they need to counteract passive transport

Passive transport summary

Transport proteins pushing particles against their natural direction (from low high concentration)

Requires ATP energy

Active transport

If active and passive transport = each other, then no overall change occurs

This is cell homeostasis – using energy to maintain the right, unequal conditions

A balancing act

Macromolecules are usually too large to fit in transport proteins

A piece of membrane folds in or out, forming vesicle around particle

Endocytosis = coming in

Exocytosis = going out

Transporting large particles

Here, we’ll study how cells make exact copies

Why?

1. Growth

2. Replacing damaged cells

3. Reproduction (not everybody – not humans)

Making new cells

Why not grow by increasing cell size?

Growing by increasing cell number

Conclusion: diffusion occurs faster in smaller cells (nutrients in, wastes out)

Goal: Get a copy of DNA to the new cell

Basic steps:

1. Copy DNA

2. Pack and split up DNA copies

3. Split up cytoplasm into two separate cells

Making a new cell copy

= replication (more in genetics unit)

Very simple – called binary fission

Much less DNA than eukaryotes, so only packs up into one chromosome

Prokaryotic cell division

Much more complex cells, so more DNA to organize (multiple chromosomes)

Eukaryotic cell division

Eukaryotic organism

# of chromosomes in each body cell

46 chromosomes in human cells note: doesn’t look like this in nucleus

actually one chromosome tied together with its exact copy

DNA’s two different forms 1) fully packed up = chromosome form –

ONLY appears during cell division 2) unpacked = thin chromatin –

DNA code can be read to make proteins

involves mitosis – more complex chromosome organization

Eukaryotic cell division

Interphase

Mitosis

Cytokinesis

Eukaryotic cell’s life cycle

normal cell activity – most cells here

DNA in thin chromatin form

if cell signaled to divide, DNA is copied

DNA packed up into chromosomes (copies tied together)

Xs lined up in 1 line, split up

DNA unpacks back into chromatin

2 cells separate, both return to interphase

Eukaryotic cell’s life cycle

DNA as chromatin

Interphase

if signaled, cell copies DNA

Early mitosis

pack up DNA into chromosomes

build cytoskeleton fibers to pull Xs

Eukaryotic cell’s life cycle

Mitosis

One line of Xs

Eukaryotic cell’s life cycle

MitosisLate mitosis / cytokinesis

DNA unpacks back to chromatin

cytokinesisstarting

both cells return to interphase

Binary fission or mitosis:

2 cells that are genetic copies of original cell(if DNA is copied correctly)

End results

Normal cells

Know when to divide(they are signaled)

Know when to stop dividing

Cell division is regulated

Body cells with messed up signaling pathways

Continue to divide out of control

Tumor = ball of dividing cells

Cancer cells

Cells need resources to survive long-term

Cancerous tumors starve normal body cells, lead to eventual death

What makes cancer benign? Malignant? We don’t know

Why is cancer a problem?

Cancer is complicated

Damaged DNA code = damaged signal pathways possible cancer

What damages DNA?

High energy waves (UV rays, X-rays)

Chemicals (in cigarette smoke, ex)

Poor diet

What causes cancer?

Benign tumors = local surgery

Malignant tumors that have spread = chemotherapy (targets ALL dividing cells)

How do we treat cancer?