2.3 Cell Boundaries - Membrane, Wall, Skeleton

Cell Boundaries

Cell membrane, cell wall, cytoskeleton, active and passive transport

Can you imagine yours classes being done in the hallway?

...or live on the streets?

...or your country not being open and exposed to everyone?

Even cells can't imagine being too open and exposed!

Cells just like your class, your family, and your nation, would be in a much organized situation if it is confined in a safe place.

Multiple Select

Which of the following are considered boundaries? (select all possible answers)

• cell membrane

• cell wall

• nuclear envelope

• chloroplast?

Multiple Select

Which of the following describes the cell membrane? (select all that applies)

• fluid

• semipermeable

• single layer

• nonpolar

Cell Membrane

Cells are made of boundaries that compartmentalize and separate them from their surroundings. All cells are made of cell membrane. Cell membrane is composed of a bilayer of phospholipids mixed with proteins, and carbohydrates.

Lipid Bilayer

cell have 2 layers of phospholipids, the heads that are on the outer part are hydrophilic (polar) and the tails on the inside are hydrophobic (nonpolar)

phospholipids reorient themselves

The polar heads always attaches themselves to the water and the non-polar tails move away from where the water is.

Multiple Select

(Check all that applies) Other than phospholipids, what else can you see in the membrane?

• cholesterol

• carbohydrates

• proteins

• nucleic acids

Multiple Choice

Which of the following things can pass through the membrane freely?

• large charged particles

• small polar substances

• small uncharged substances

• salts

Multiple Choice

Which of the following helps substances enter if they cannot easily diffuse inside the cell?

• carbohydrates

• proteins

• lipids

• nucleic acids

Multiple Choice

Which of the following helps cells maintain their fluidity?

• cholesterol

• glycoproteins

• saturated fatty acid tails

• glycoproteins

Cholesterol

Cholesterol is an important component of the cell membrane. Cholesterol is its basic component, accounting for more than 20% of plasma membrane lipids. According to a study feeding animals with foods lacking in cholesterol resulted in increased red blood cell fragility in these animals, which easily caused cell rupture. Studies have shown that when the temperature is high, cholesterol can prevent the disorder of the bilayer; when the temperature is low, it can interfere with its ordering, prevent the formation of liquid crystals, and maintain its fluidity. Therefore, it is conceivable that if there is no cholesterol, cells will not be able to maintain normal physiological functions and life will end.

Proteins

The phospholipid bilayer is embedded with so many proteins. Some of them are positioned from the outside to the inside of the cell traversing the bilayer of phospholipids. Some are only located outside where carbohydrates and lipds can be attached, some are only inside, and some are hollow, which allows substances to enter, acting much like a gate.

Charged particles

Substances with charges, including polar compounds, may be attracted to the polar heads of the phospholipids. But they will not easily diffuse inside the cell because of the fat layer underneath the polar heads. The only way they can enter is through using protein gates. Not all substances can diffuse or enter cells, that's why we call it, "semi-permeable".

Multiple Select

Select all that applies.

Which of the following describes the cell membrane?

• polar

• semi-permeable

• fluid

• mosaic

Fluidity of Membrane

The components of the membrane are include things that can constantly move-hence, they are fluid. This fluidity can be associated with the kind of tails of the phospholipids and the presence of cholesterol. The phospholipids are composed of saturated and unsaturated fat. Because of their shape, they cannot stack together that easily, and together with the cushioning effect of cholesterol, they are able to move around constantly.

Fluid Mosaic

The fluid mosaic model of the cell membrane is how scientists describe what the cell membrane looks and functions like, because it is made up of a bunch of different molecules that are distributed across the membrane. The movement of the mosaic of molecules makes it impossible to form a completely impenetrable barrier.

Selective Permeability

–Selective = choosey

–Permeable = allow things to cross

–Remember: Cell membrane Regulates what can cross the membrane like a security guard

Glycoproteins

One of the molecules found in the fluid mosaic model of the cell membrane are glycoproteins. There are markers of the cells that are used to recognize each other and transmit signals through receptors in the form of glycoproteins.

Multiple Choice

What are cell walls for?

• to control the amount of salts that enter the cell

• to transport materials from the ER to other cell parts

• to protect the cells from bursting in hypotonic environments

• to protect the cells from dividing uncontrollably

Multiple Select

Select all that applies.

Which kind of cells may have cell wall?

• animals

• plants

• fungi

• bacteria

Cell Wall

A cell wall is a structural layer surrounding some types of cells (plants, fungi, and some bacteria), just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism.

Cell Wall

Cell wall of plants are made of cellulose.

Cell wall of fungus are made of chitin.

Cell walls protect cells from bursting

When cells are placed in hypotonic environment, they tend to take in a lot of water. Without the cell wall, cells tend to burst as the cannot hold the pressure anymore.

Multiple Choice

Which of the following are true regarding osmosis in animal cells?

• Cells in hypertonic solution gains and loses equal amount of water so it keeps its size and shape.

• Cells in an isotonic solution loses a lot of water and then shrinks

• Cells in a hypotonic solution tends to burst when they take too much water.

Multiple Choice

Which of the following is not properly paired?

• Cell wall = porous

• Cytoskeleton = jelly-like substance in cells

• Centrioles = helps in cellular division.

Multiple Select

What are the primary roles of the cell membrane?

• to set the boundary of the cell

• to regulate what goes in and out of the cell

• to