A/P 1 Quiz 3

The Cellular Level of Organization

Structures of a Cell

Parts of a Cell

The cell can be subdivided into 3 parts:

1. Plasma (cell) membrane

2. Cytoplasm

•

Cytosol

•

Organelles

3. Nucleus

•

Chromosomes

•

Genes

*The Plasma Membrane

The plasma membrane is a flexible, sturdy
barrier that surrounds/contains
cytoplasm of cell

Membrane Proteins

Two types of membrane proteins

1. Integral (also called transmembrane) proteins
2. Peripheral proteins

*Membrane Permeability

Plasma membranes are selectively permeable

❑ The lipid bilayer is always permeable to small,

nonpolar, uncharged molecules

❑ Transmembrane proteins that act as channels or

transporters increase the permeability of the
membrane

❑ Macromolecules are only able to pass through the

plasma membrane by vesicular transport

*Functions of
Membrane Proteins

❑ The different proteins

help determine many
of the functions of
the cell membrane

*Membrane Fluidity

◼ Membranes are fluid structures because most of the membrane lipids and many of the membrane proteins move easily in the bilayer

❑ Membrane lipids and proteins are mobile in their

own half of the bilayer

◼ Cholesterol serves to stabilize the membrane and reduce membrane fluidity

*Gradients Across the Plasma
Membrane

◼ A concentration gradient is the difference in

the concentration of a chemical between one
side of the plasma membrane and the other

◼ An electrical gradient is the difference in

concentration of ions between one side of the
plasma membrane and the other

◼ Together, these gradients make up an

electrochemical gradient

*Transport Across the Plasma
Membrane

Transport processes that move substances
across the cell membrane are:

❑ Passive processes

◼ Simple diffusion

◼ Facilitated diffusion

◼ Osmosis

❑ Active processes

◼ Primary and Secondary transport

◼ Vesicular transport

*Passive Transport: Simple Diffusion

Diffusion is influenced
by:

1. Steepness of the

concentration
gradient

2. Temperature
3. Mass of diffusion

substance

4. Surface area
5. Diffusion distance

*Passive Transport: Facilitated
Diffusion

Transmembrane proteins help solutes that are
too polar or too highly charged move through
the lipid bilayer

The processes involved are:

❑ Channel mediated facilitated diffusion

❑ Carrier mediated facilitated diffusion

*Passive Transport: Osmosis

The net movement of a solvent through a
selectively permeable membrane from an area
of high concentration to an area of low
concentration

*Tonicity

Tonicity of a solution relates to how the solution
influences the shape of body cells

*Active Transport: Primary

Energy derived from ATP changes the shape of
a transporter protein which pumps a substance
across a plasma membrane against its
concentration gradient

*Active Transport in Vesicles:
Exocytosis & Transcytosis

◼ Exocytosis – membrane-enclosed secretory

vesicles fuse with the plasma membrane and
release their contents into the extracellular
fluid

◼ Transcytosis – a combination of endocytosis

and exocytosis used to move substances
from one side of a cell, across it, and out the
other side

*Passive Transport: Secondary

Energy stored (in a hydrogen or sodium
concentration gradient) is used to drive other
substances against their own concentration
gradients

*Cytoplasm

The cytoplasm has 2 components:

1. Cytosol - also known as the intracellular fluid

portion of the cytoplasm

2. Organelles - the specialized structures that have

specific shapes and perform specific functions

*Peroxisomes

Peroxisomes are structures that are similar in
shape to lysosomes, but are smaller and
contain enzymes that use oxygen to oxidize
(break down) organic substances

*Proteasomes

Proteasomes are barrel-shaped structures that
destroy unneeded, damaged, or faulty proteins
by cutting long proteins into smaller peptides

*Nucleus

◼ The nucleus

contains the
hereditary units of
the cell, called genes

◼ Genes are arranged

along chromosomes

*Protein
Synthesis:
Transcription

Transcription occurs in
the nucleus and is the
process by which
genetic information
encoded in DNA is
copied onto a strand of
RNA to direct protein
synthesis

*Protein Synthesis: Translation

Translation occurs outside the nucleus and is
the process of reading the mRNA nucleotide
sequence to determine the amino acid
sequence of the newly formed protein

*Cell Division

Cell division is a process by which cells
reproduce themselves

❑ Cell cycle

*Mitosis

◼ Mitosis occurs when the nucleus of a cell

divides

◼ Mitosis results in the distribution of 2 sets of

chromosomes into 2 separate nuclei

◼ Mitosis is divided into 4 steps:

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

*Mitosis: Prophase

During prophase chromatin condenses into
chromosomes and the nuclear membrane
disappears and centrosomes move to opposite
poles

*Mitosis: Metaphase

During metaphase centromeres of
chromosomes line up at the metaphase plate

*Mitosis: Anaphase

During anaphase centromeres of chromosomes
split and sister chromatids move toward
opposite poles of the cell

*Mitosis: Telophase

During telophase the mitotic spindle dissolves,
chromosomes regain their chromatin
appearance, and a new nuclear membrane
forms

*Cytokinesis

During cytokinesis
a cleavage furrow
forms and
eventually the
cytoplasm of the
parent cell fully
splits

❑ When this is

complete,
interphase begins

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*Control of Cell Destiny

3 possible destinies:

1. Remain alive and functioning without dividing

2. Grow and divide

3. Die

Aging and Cells

As we age:

❑ Our cells gradually deteriorate in their ability

function normally and in their ability to respond to
environmental stresses

❑ The numbers of our body cells decreases

❑ We lose the integrity of the extracellular

components of our tissues