Cell Structure and Function

Robert Hooke

● 1665 – English scientist Robert Hooke viewed dead cork cells for the first time using a light microscope

● He described them as “a great many little boxes” that reminded him of the cubicles or “cells” where monks lived

Anton van Leeuwenhoek

● 1673 – First person to view living cells, a Dutch trader

● Observed microorganisms and called what he saw “animalcules”

Schleiden, Schwann, & Virchow

● 1838 – German botanist Matthias Schleiden concluded that all plants are composed of cells

● 1839 – German zoologist Theodor Schwann concluded that all animals are made of cells

● German physician Rudolf Virchow concluded that all cells come from other cells

The Cell Theory

● All living organisms are composed of one or more cells

● Cells are the basic units of structure and function in an organism

● Cells come only from the reproduction of existing cells

Cell Diversity

● A cells function influences its physical features, example: a nerve cell is much different than a skin cell because they each perform very different functions (p. 72 in book)

● Cells come in many different sizes but most are about 1/500 the size of the period at the end of this sentence.

Surface Area-To-Volume Ratio

● The size of a cell is limited by the relationship of the cell’s outer surface area to its volume (surface area-to-volume ratio)

● Materials needed by a cell and waste products produced by the cell must pass into and out of the cell through the surface

● If a cell gets too big, the volume would increase much more than the surface area and the materials could not enter or leave the cell fast enough to meet the cell’s needs

What Do All Cells Have In Common?

● All cells have a cell membrane (plasma membrane) that covers its surface and acts as a barrier between the inside and the outside of a cell. All materials enter and exit through it.

● All cells have an area inside the cell membrane called the cytoplasm. This includes everything but the nucleus. The part of the cytoplasm that includes molecules and particles without membranes (ribosomes) is called the cytosol.

Common Cellular Structures Continued

● All cells carry coded information in the form of DNA for regulating their functions and reproducing themselves

● Some cells have DNA floating freely in the cell

● Others Have a membrane-bound organelle that contains the DNA called the nucleus

Prokaryotes● Organisms that lack a

membrane-bound nucleus and membrane-bound organelles

● Area where DNA resides is called the nucleoid

● Example: bacteria

Eukaryotes

● Organisms made of one or more cells that have a nucleus and membrane-bound organelles are called eukaryotes

● Eukaryotic cells are generally much larger than prokaryotic cells

Cell (Plasma) Membrane● Made of phospholipids● The heads are polar

(water loving)● The tails are nonpolar

(water-fearing)● Phospholipids line up so

that their tails point inward and heads outward creating a phospholipid bilayer

● Job: gateway to the cell, allows substances to enter and exitWater molecules surround the

plasma membrane

Integral Proteins

● Proteins found within the cell membrane● Cell surface markers – identify cell type● Receptor proteins – recognize and bind to

substances outside the cell (ex. hormones)

● Enzymes – assist chemical reactions inside the cell

● Transport proteins – help substances move across the cell membrane

Nucleus● Job: houses and protects the

cells DNA in eukaryotes

● Filled with a jellylike substance called nucleoplasm

● Surrounded by a double membrane called the nuclear envelope (2 phospholipid bilayers)

● Nuclear pores: wholes in the envelope that allow substances to enter and exit

● Nucleolus: site where DNA concentrates when it is in the process of making ribosomes

Mitochondria

● Job: convert glucose into energy (ATP) adenosine triphosphate

● Cell’s powerhouse● Active cells (muscle

cells) have more mitochondria than less active cells (fat cells)

Mitochondria continued

● Outer phospholipid membrane separates it from the cytosol

● Inner phospholipid membrane has many folds called christae that contain proteins that carry out the chemical reactions that create energy (ATP)

● Have their own DNA and can reproduce by the division of preexisting mitochondria

Ribosomes● Job: build proteins● Do not have a membrane● Ribosome assembly

begins in the nucleolus and ends in the cytoplasm

● Made of one large and one small subunit that come together

● Ribosomes that float freely in the cytoplasm create proteins used in chemical reactions occurring within the cytoplasm

Endoplasmic Reticulum

● Job: production and transportation of substances within the cell (the cells highway)

● Two types : rough and smooth● Rough ER has ribosomes attached to the

outside of the membrane (smooth does not)

Smooth ER

ROUGH ER● Interconnected network of thin folded

membranes(composition much like cell membrane)

● Interior of this maze is called the lumen● Production of proteins occurs both on the surface

of the ER and inside the lumen● As a protein is being made on a ribosome

attached to rough ER, it enters the lumen. Once inside it can be modified by adding sugar chains to it which can help the protein fold to the right shape (protein shape determines its function)

● Proteins made on the ER are either incorporated into the cell membrane or secreted out of the cell

SMOOTH ER

● Lacks ribosomes, smooth appearance● Most cells contain very little smooth ER● Builds lipids like cholesterol ● Builds hormones like estrogen in the

ovaries and testosterone in the testes ● Releases calcium in muscles to stimulate

contraction● Detoxifies drugs and poisons in the kidney

and liver cells

Golgi Apparatus

● System of flattened, membranous sacs

● The helper of the endoplasmic reticulum

● Receives vesicles from the ER containing lipids or proteins and transports them

● Along the way the substances can be modified and marked with “address labels” that tell the cell where the package needs to go

Vesicles

● Cells need to separate reactants for various chemical reactions until it is time for them to be used

● Vesicles are membrane bound sacs that divide some materials from the rest of the cytoplasm and transport these materials from place to place within the cell

● Vesicles are usually short lived and are formed and recycled as needed

● Vesicles are often pinced off of the ER and transported to the golgi apparatus where it will merge and unload its contents

● Once there, necessary modifications are made the protein is packaged inside a new vesicle and either stored, transported to a new location within the cell, or secreted by the cell

Lysosomes● One kind of vesicle● Bud off of the golgi

apparatus and contain digestive enzymes that break down organic compounds and bacteria

● Within a cell, lysosomes digest worn-out organelles (autophagy)

● Break down cells when it is time for them to die, if they no longer function properly, or if there is too many of them (autolysis)

Cytoskeleton

● A network of thin tubes that crisscrosses the cytosol (microtubules,microfilaments, and intermediate filaments)

● Gives shape to the cell from the inside like tent poles do for a tent

● Act as a system of tracks that guide organelles and molecules as they move within the cell

● Hold organelles in place

Centrioles● The centrosome is a

small region of cytoplasm that produces microtubules

● In animal cells the centrosome contains two small structures called centrioles

● The centrioles are made up of microtubules and are used during animal cell division

● Centrioles also organize microtubules to form cilia and flagella

Cilia and Flagella

● Hairlike structures that extend from the surface of a cell and help with movement

● Cilia are short and there are many of them when present● Flagella are long and far less numerous than cilia when

present● There motion forces liquid past a cell which in unicellular

organisms results in “swimming” but for cells anchored in tissue (multicellular) this motion sweeps liquids across the cell

Plant Organelles

● Cell wall

● Central Vacuole

● Plastids● Chloroplasts● Chromoplasts

Cell Wall

● Rigid layer that lies outside the cell’s plasma membrane

● Contain a carbohydrate called cellulose

● Form a stiff box around each cell

● Pores in it allow water and other molecules to enter and exit

Secondary Cell Wall

● Produced by plants like trees

● When cell stops growing it secrets a secondary cell wall between the plasma membrane and primary cell wall

● It is strong but cannot expand, the cell inside dies and disintegrates (ex. wood)

Central Vacuole

● Large, fluid-filled organelle that stores water, enzymes, and wastes

● Can make up 90% of plant’s cell volume and pushes all other organelles to the side

● When vacuoles are full the plant stands upright, when empty the plant wilts

Plastids

● Organelles that are surrounded by a double membrane and contain their own DNA

● 2 kinds : chloroplasts and chromoplasts

Chloroplasts

● A plastid that contains sacs called thylakoids

● Thylakoids contain a green pigment called chlorophyll

● Chlorophyll captures light energy to fuel photosynthesis

Chromoplasts

● A plastid that contains colorful pigments that may or may not take part in photosynthesis

● Examples: filled with carotene to give carrots orange color or flower petals of many different colors