Chapter 4 Structure and Function of the Cell



Chapter 4 Structure and Function of the Cell

1. Introduction to the cell

A. In 1665, the English scientist Robert Hooke used a microscope to examine a thin slice of cork

1. He said it consisted of “tiny little boxes”. These boxes reminded him of the place where monks lived, therefore, he called them cells

2. What he actually looked at were dead plant cells

3. The first person to look at live cells was a Dutch scientist and microscope maker by the name of Anton van Leeuwenhoek

2. State the cell theory

A. This theory was proven by the botanist Matthias Schleiden, who said all plants are composed of cells; Theodor Schwann, a zoologist who said all animals were composed of cells; and Dr. Rudolph Virchow, who reasoned that disease causing cells only arose from other cells

B. The theory has 3 parts:

1. All living things are made of one or more cells

2. Cells are the basic units of structure and function in living organisms

3. Cells only come from existing cells by reproduction

C. Cell diversity – not all cells are alike – vary in size, shape, and internal organization

1. Two main types of cells

a. Prokaryotes (means w/o nucleus) – have no nucleus or membrane-bound organelles

b. Eukaryotes (means true nucleus) – have a true nucleus and many membrane-bound organelles

2. Size

a. They are very small and most can only be seen with a microscope.

1. b. The have a larger surface-area-to-volume ratio

1) When a cell grows, it retains it shape, but it’s volume will increase more than it’s surface area

2) This allows for nutrients, oxygen, and other materials the cell needs to enter the cell faster, because the distance they have to travel is so small

3. Shape

2. a. Cells come in a variety of shapes. Their shape reflects their function

1) Nerve cells have extensions so that they can conduct impulses, skin cells are flat so they can cover the body’s surfaces, and white blood cells can change shape, so that they can move around and get to the area of an infection

4. Internal Organization

3. a. Cells contain a variety of organelles

1) An organelle is a cell component that performs a specific function

4. b. All cells have a cell membrane (a.k.a. plasma membrane)

1) This protects the cell and holds all of the inside stuff in

2) The cell membrane is selectively permeable, which means it only lets certain

things into and out of the cell

3) Cell membranes are made primarily of lipids and proteins

a) One of the major types of lipids is the phospholipids -

Phospholipds have a hydrophilic polar head and a hydrophobic non- polar tail

b) Because cells are filled with water and are surrounded by

water, the phospholipids will fold over so that a bilayer is formed

c) This bilayer has the hydrophilic heads touching the water

and the hydrophobic tails in the middle, so they don’t touch the water

d) Cell membranes also have protein attached to its surface

i. Peripheral proteins: located on the interior or exterior

of the cell

ii. Integral proteins: span from the interior to the exterior

of the cell or can be found on the interior or exterior of the cell

iii. Marker proteins help other cells recognize their cell type

iv. Receptor proteins recognize and bind to specific

substances

v. Transport proteins aid in the movement of substances

into and out of the cell

3. Evolution of multicellular organization

A. Through competition for resources, cells with adaptations evolved

1. Example: unicellular eukaryotes may have begun to live in colonies with other cells of the same kind

a. These associations are called colonial organisms

1) Example: the Volvox

2) Each cell maintains its own existence but many of the cells perform specific functions that benefit the entire colony

4. Name the major organelles found in a eukaryotic cell, and describe their function

A. Cell Membrane - selectively permeable phospholipid bilayer – controls the ease which substances pass in or out of the cell – some things like water come and go with ease others things can’t come or go at all

B. Cytoplasm – between the cell membrane and the nucleus and containing the organelles

C. Cytosol – liquid gelatin-like aqueous fluid with dissolved salts, minerals, and organic molecules

D. Mitochondria – sites of chemical reactions that transfer energy from organic compounds to ATP - power house of the eukaryotic cell

1) double membrane bound organelle

a. The smooth outer membrane is a boundary between the organelle and the cytosol

b. The inner membrane has many long folds called cristae

i. These cristae greatly increase the surface area of the mitochondria, thus providing more space for chemical reactions to take place

2) has its own DNA

a. Arise only when existing mitochondria grow and divide

b. The number in a cell depends on how much energy the cell needs

c. Basically are cells within cells – Endosymbiotic theory

E. Ribosomes – most numerous organelle – not bound by a membrane

1) In both prokaryotes and eukaryotes

2) some remain free floating in the cytosol

3) some attach to the endoplasmic reticulum of eukaryotic cells making it rough

4) play an important role in the synthesis of protein

a. proteins used within the cytosol are made by the ribosomes floating free

b. proteins used in the membranes or exported from the cell are made by the ribosomes attached to the endoplasmic reticulum

F. Endoplasmic Reticulum - ER – system of membranous tubules and sacs

1) functions as a intracellular highway for molecules to move around the cell

2) two types

a. Rough endoplasmic reticulum - has ribosomes attached to it

1) found in cells that make large amounts of proteins that are exported from the cell or inserted into the membrane

b. Smooth endoplasmic reticulum - does not have ribosomes attached

1) involved in the making of steroids in gland cells, regulations of calcium levels in muscle cells, and the breakdown of toxic substances by liver cells

G. Golgi apparatus

1) processing, packing, and secreting organelle

2) system of membranes as a series of convex flattened sacs with one way traffic

3) works with the ER to modify proteins for export from the cell

H. Lysosomes

1) small, spherical organelles that enclose hydrolytic enzymes within single membranes

2) hydrolytic enzymes can digest proteins, carbohydrates, lipids, DNA, and RNA as well as old organelles, viruses, and bacteria

3) They also play a role in development biology

a. Example: the formation of fingers in humans – dissolve tissue between fingers

I. Cytoskeleton

1) network of protein strands (not surrounded by membranes) in the cytosol that function in support and movement of organelles

2) two types

a. Microfilaments – smallest strands of the cytoskeleton

1) function in cell movement and in contraction of muscle cells

b. Microtubules – largest strands of the cytoskeleton

1) spindle fibers – bundles of microtubules thick enough to be seen with a light microscope – assist in the movement of chromosomes during cell division

J. Cilia and Flagella – hair-like organelles that extend from the cell assisting in movement

a. Cilia – short and numerous

1. function in movement for many unicellular organisms

2. function to trap debris in your respiratory tract where their movement sweeps the debris to the back of your throat so you can swallow it

b. Flagella – long and few

1. function in locomotion of the cell

2. sperm cells move by whipping the flagella back and forth

c. structure – both are made of nine pairs of microtubules arranged around a central pair

K. Nucleus – stores genetic material of eukaryotic cells

1) Nuclear matrix – protein skeleton that helps maintain shape of the nucleus

2) Nuclear envelope - double membrane surrounding the nucleus with nuclear pores through which RNA travels out of the nucleus

a. Chromatin – combination of DNA (hereditary information) and proteins

b. Chromosomes – chromatin strands coiled up and densely packed when a cell is about to divide

c. Nuclear pores – small holes in the nuclear envelope through which RNA (copies of DNA from which proteins can be made) can pass

3) Nucleolus – spherical area where ribosomes are made and partially assembled before they are transported out through nuclear pores into the cytosol

L. All cells have DNA

5. 1) This is the genetic material. DNA contains the instructions for making proteins, regulating cellular activities, and enabling cell division

2) Organisms who store their DNA in a large organelle near the center of the cell (nucleus) are called Eukaryotes

a) Eukaryote: an organism whose cells contain a membrane-bound nucleus and other membrane-bound organelles

b) Eukaryotic DNA is in short linear rods

3) Organisms whose DNA floats freely in the cytoplasm are called prokaryotes

a) Prokaryote: a unicellular organism that lacks membrane-bound nucleus and other membrane-bound organelles

b) Prokaryotic DNA is a single, circular strand attached to the inside of the cellular membrane

c) Example: Bacteria

5. Describe three structures characteristic of plant cells

A. Cell walls – rigid wall for support and protection – outside the cell membrane

a. made of cellulose a complex carbohydrate – large numbers of glucose monomers linked in long, straight chains that formed hydrogen bonds with each other

b. two types

1. Primary cell wall – develops just outside the cell membrane and grows with the cell

2. Secondary cell wall – develops between the primary cell wall and the cell membrane

a) is tough and woody

b) does not allow the cell to grow any more

B. Vacuoles

a. quite large – up to 90% of the cell volume

b. fluid-filled organelles that store enzymes and metabolic waste

C. Plastids - organelles that are double membrane-bound and have their own DNA – some store fats others contain pigments that absorb light

a. Chloroplasts – most familiar plastid

1. encloses a system of flattened membranous sacs called thylakoids

2. organelles in which the energy of the sun is converted into chemical energy in organic compounds – in the process called photosynthesis

3. contain large amounts of the green pigment chlorophyll making leaves and plants green

6. Distinguish between tissues, organs and organ systems

1) Tissues – groups of cells that carry out a specific function – outer layer of skin, nervous tissue, muscle tissue

2) Organ – several types of tissues that interact to perform a specific function – Stomach: muscle tissue causes movement, epithelial tissue secretes enzymes, connective tissue holds the stomach together, and nervous tissue sends messages back and forth to the brain

3) Organ system – group of organs that work together to perform a set of related tasks – respiratory system, nervous system, digestive system which includes the mouth, esophagus, stomach, intestines, etc. make up the digestive system

4) The different organ systems interact to carry out the processes of life in an organism

Chapter 4 Structure and Function of the Cell

□ A cell is the smallest unit that can carry on all of the processes of life. The development of the microscope enabled scientists to take their first close look at cells.

□ The cell theory states that (1) all living things are composed of one or more cells, (2) cells are the units of structure and function in an organism, and (3) cells come only from preexisting cells.

□ The ratio of surface area to volume determines how large a cell can get. Most plant and animal cells are only about 10 to 50 μm in diameter.

□ A cell’s shape reflects its function.

□ Eukaryotic cells contain a nucleus and membrane-bound organelles, but prokaryotic cells have neither.

□ The cell membrane is selectively permeable and consists mostly of lipids and proteins. Both move constantly within the membrane, as described by the fluid mosaic model.

□ Mitochondria are organelles in which the energy in organic compounds is transferred to ATP. Mitochondria are surrounded by a double membrane.

□ Ribosomes are involved in the synthesis of proteins. Some ribosomes are free in the cytosol. Others are attached to the rough endoplasmic reticulum, which prepares proteins for export from the cell or insertion into the cell membrane. The smooth endoplasmic reticulum lacks ribosomes.

□ The Golgi apparatus is the cell’s processing, packaging, and secreting organelle.

□ Lysosomes contain hydrolytic enzymes that digest organic compounds, old cell parts, and other materials.

□ The cytoskeleton includes microfilaments and microtubules, strands of protein that help cells move and maintain their shape.

□ Cilia and flagella assist in cell movement. Both are made of nine pairs of microtubules arranged around a central pair.

□ The nucleus is surrounded by a double membrane and contains chromatin, a combination of DNA and protein. DNA stores hereditary information and directs the synthesis of RNA. RNA directs the synthesis of proteins in the cytosol.

□ Plant cells contain three structures not found in animal cells: cell walls, vacuoles, and plastids.

□ A rigid cell wall covers the cell membrane in plant cells and provides support and protection.

□ Large fluid-filled vacuoles store enzymes and waste products within plant cells.

□ Plastids store starch, fats, and pigments in plant cells. One type of plastid, the chloroplast, is the site where light energy is converted into chemical energy during photosynthesis.

□ The cells in most multicellular organisms are organized into tissues, organs, and organ systems.

□ The earliest cells on Earth were probably single-celled prokaryotes. Unicellular eukaryotes evolved later, followed by multicellular organisms.

□ A colonial organism is a group of genetically identical cells that live together in closely connected groups. Some of the cells that make up a colonial organism are specialized to perform certain tasks, like movement or reproduction.

Vocabulary List

Cell

Cell membrane

Cell theory

Cell wall

Chloroplast

Chromatin

Chromosome

Cilium

Crista

Cytoplasm

Cytoskeleton

Cytosol

Eukaryote

Flagellum

Golgi apparatus

Lysosome

Microfilament

Microtubule

Mitochondrion

Nuclear envelope

Nuclear matrix

Nuclear pore

Nucleolus

Nucleus

Organ

Organ system

Organelle

Plastid

Prokaryote

Ribosome

Rough endoplasmic

reticulum

Selectively permeable

membrane

Smooth endoplasmic

reticulum

Spindle fiber

Thylakoid

Tissue

Vacuole

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