Cell Structure and Function

Chapter 4

Who decided to name a call a cell a cell?Robert Hooke

• English scientist that used a crude microscope to look at cork• it appeared to be “a lot of tiny boxes” • reminded him of monks and called them cells in 1665

The observations of many scientist led to this…Cell Theory

1. All living things are made of one or more cells2. Cell are the basic unit of structure and function in organisms3. All cells arise from existing cells

Cell DiversityCells are diverse in terms of shape, size, and internal organization.

Cell shapes reflects the different functions of cells

Two Basic Types of Cells• Prokaryotes– Lack a

membrane-bound nucleus

– Lack membrane-bound organelles

– Their DNA is often concentrated in a part of the cell called the nucleoid

– Divided into the domains of Bacteria and Archaea

• Eukaryotes– Have a nucleus– Have membrane-

bound organelles– Have subcellular

structures called organelles (well-defined, intracellular bodies that perform specific functions for the cell)

– Are generally much bigger than prokayrotes

http://www.blobs.org/science/article.php?article=27

3 basic parts common to all cells types:

1. Plasma membrane = Cell membrane• cell’s outer boundary• covers cell’s surface• acts as a barrier between the inside and outside of a cell

2. Cytoplasm• region within plasma membrane, including fluid, cytoskeleton, and all organelles except nucleus

3. Nucleus• membrane bound structure• controls cells functions• carry coded information – DNA• only in Eukaryotic cells

• a group of similar cells and their products that have a specific function

• groups of tissues that perform a particular job in an organism (ie. stomach, liver)

• a group of organs that accomplish related tasks (ie. digestive system)

Organism – combination of several organ systems

Cell Organelles and Features Plasma Membrane (cell membrane)

allows certain molecules to enter or leave cell separates internal metabolic reactions from the external

environment allows cell to excrete waste and interact with its environment made up of phospholipids

Plasma membrane continued…

Sterols – lipids between the tails of phospholipids- makes the membrane more firm and prevent the

membrane from freezing at low temperatures

- major one in animal cells is cholesterolIntegral proteins – specific proteins embedded within the lipid

bilayer - are able to detect

environmental signals and transmits them to the

inside of the cell - actively transports

molecules into the cell

Carbohydrates – attached to proteins- acts as labels that help cell recognize

each other and stick together- viruses can use these labels as docks

for entering and infecting the cell

Nucleus

houses and protects the cell’s genetic information

site where DNA is transcribed into ribonucleic acid (RNA)

when cell is not dividing, DNA exists in the form of a long, thin structures called chromatin

when cell is about to divide, DNA condenses to form chromosomes

chromosomes – are structures in the nucleus made of DNA and protein

DNA in the Nucleus• Chromatin – when DNA is in the form of a

threadlike material (this occurs when the cell is not dividing)

• Chromosomes – structure in the nucleus made up of DNA and RNA (when chromatin condenses when a cell is about to divide)

http://micro.magnet.fsu.edu/cells/nucleus/images/chromatinstructurefigure1.jpg

What is inside the nucleus?• nucleoplasm – jellylike liquid which holds the contents of the nucleus; similar to cytoplasm

• nuclear envelope – double membrane that surrounds the nucleus; made up of 2 phospholipid bilayers

What is inside the nucleus?• nuclear pores– tiny, protein-lined holes covering the surface of the nuclear envelope; provides passageway for RNA and other materials to enter and leave nucleus

• nucleolus – dense area in nucleus; where DNA is concentrated when it is in the process of making ribosomal RNA

Ribosomes• Small, roughly spherical• Made up of a large and a small subunit• Site of protein synthesis• Are made up of protein and RNA• Are found on rough ER as well as throughout the cytoplasm

Mitochondria – “power house”• tiny organelles that transfer energy from organic molecules to ATP

• hundreds on highly active cells (ie. muscle cells)

• few on not very active cells (ie. fat-storage cells) • have inner and outer phospholipid membrane

• inner membrane has cristea –contains proteins

• contains their own DNA

Mitochondrial DNA

Scientists think that mitochondria originated from prokaryotic cells that were incorporated into ancient Eukaryotic cells.

This symbiotic relationship provided the prokaryotic invaders with a protected place to live and provided the eukaryotic cell with an increased supply of ATP

Endoplasmic Reticulum - ER

• system of membranous tubes and sacs (cisternae)

• functions as a path along which molecules move from one part of the cell to another

• two types: Rough ER and Smooth ER

Rough ER• interconnected, flattened sacs covered with ribosomes• produces phospholipids and proteins• ie make digestive enzymes

Smooth ER• lacks ribosomes• cells contain very little• builds lipids such as cholesterol• locations:• Ovaries/testes – produces

the steriod hormones estrogen and testerone• skeletal and heart muscle –

releases calcium, which stimulates contraction• liver and kidney – helps

detoxify drugs and poisons• Long term abuse leads to

more smooth ER

Golgi Apparatus• system of flattened, membranous sacs

• modify vesicle contents as they move along

• proteins get “address labels” that direct them to other parts of the cell

• can add carbohydrate labels to proteins or alter new lipids in various ways

Vesicles

• small, spherical shaped sacs surrounded by a single membrane and are classified by their contents

• often migrate to merge with plasma membrane, releasing their contents outside of the cell

• cells contain several types, which perform various roles

• some types of vesicles are lysosomes, peroxisomes, glyoxysomes, and endosomes

Lysosomes• bud from Golgi Apparatus and contain digestive enzymes (breaks down proteins, nucleic acid, carbohydrates, phospholipids)• breaks down cells when it is time for them to die• maintains organisms health by destroying cells that are no longer functioning properly

Peroxisomes• not produced by Golgi Apparatus• abundant in liver and kidney cells; detoxify alcohol and other drugs• named for hydrogen peroxide (H2O2) they produce when breaking down alcohol and killing bacteria• breaks down fatty acids

Glyoxysomes

• found in seeds of some plants

• break down stored fats to provide energy

Endosome

• engulf material by surrounding it with plasma embryo, resulting in a pocket

Protein Synthesis major function in cell is production of proteins

CYTOSKELETON• network of thin tubes and filaments that crisscrosses the cytosol• give shape the same way as tent poles do for a tent• acts as a system of internal tracks on which items move around inside the cell

MICROTUBULES• hollow tubes made of protein called tubulin• radiate outward from central point – centrosome• hold organelles in place, maintains cell shape and act as tracks that guide organelles as they within the cell

MICROFILAMENTS• long threads of a beadlike protein actin and are linked end to end and wrapped around each other like 2 strands of rope• crawling white blood cells and contraction of muscle cells

INTERMEDIATE FILAMENTS• rods that anchor the nucleus and organelles to their place in cell• maintain internal shape of nucleus• hair-follicle cells produce intermediate filament proteins that make up most of the hair shaft

CILIA and FLAGELLA• hair-like structures that extend from the surface of a cell, where they assist in movement• cilia – short, present in large numbers on certain cells• flagella – longer, far less numerous on cells• membrane on outer surface and internal structure of 9 pairs of microtubules around 2 central tubules

Examples

• Cilia: • inner ear vibrate = help detect sound• covers the surface of many protists = row like oars or

sweep H2O and food into mouth-like opening

• Flagella:• propel themselves = human sperm

CENTRIOLES• 2 short cylinders of microtubules at right angles to each other and situated in cytoplasm near nuclear envelope• animal cells; organize microtubules of cytoskeleton during cell division

PLANT CELLS• have 3 additional kinds of structures that are extremely important to plant functions

• cell walls• large central vacuoles • plastids

Why are there different structures?

plants make their own carbon-containing molecules directly from carbon taken in from environment takes in CO2 and H2O and converts it into sugars

PHOTOSYNTHESIS

CELL WALL• rigid layer lies outside cell’s plasma membrane• contains carbohydrate = cellulose• cellulose – made directly on surface of plasma membrane

by enzymes that travel along membrane and are guided by microtubules

• there are two walls: primary and secondary walls• the secondary wall is when the cell stops growing it

secretes the wall between membrane and primary wall• very strong, no longer expands• ie. Wood in desks made of billions of secondary wall

cells have died and disintegrated inside

CENTRAL VACUOLE• large, fluid filled organelle that stores not only H2O but enzymes, metabolic waste, and other materials

• forms as other smaller vacuoles fuse together

• when H2O is plentiful, it fills up, cell expand and plant stands up right. During the dry period, vacuoles lose H2O, cell shrinks, vacuole shrinks, and plant wilts

• other vacuoles store toxic materials• acacia tree – store poisons that provide defense

against plant eating predators

PLASTIDS

• surrounded by double membrane and contain their own DNA

• there are several types: chloroplasts, chromoplasts, amyloplasts, leucoplasts

CHLOROPLASTS use light energy to make carbohydrates from CO2 and H2O system if flattened, membranous sacs called thylakoids

thylakoids contain green pigment = chlorophyll chlorophyll – main molecule absorbs light and

captures light energy for the cell like mitochondria, scientists believe chloroplasts are thought to be descendents of ancient, prokaryotic cells that were incorporated into plant cells through a process called endosymbiosis

CHROMOPLASTS plastids that contain colorful pigments and that may or may not take part in photosynthesis

ie carrot root cells = orange pigment ie flower petals = red, purple, yellow, or white

Amyloplasts• store starch

Leucoplasts• a colorless plastid in the cytoplasm of plant cells that makes and stores starch

COMPARING CELLS PROKARYOTES VS EUKARYOTES

Prokaryotes lack a nucleus Prokaryotes lack membrane-bound organelles Prokaryotes have a region called a nucleoid where genetic

material is concentrated

PLANT CELLS VS ANIMAL CELLS production of a cell wall by plant cells plant cells contain a large central vacuole plant cells have a variety of plastids