Eukaryotic Cell Structures

7-2

In some respects, the eukaryotic cell is like a factory

It contains several tiny specialized structures called organelles

Biologists divide the cell into 2 parts: the cytoplasm and the nucleus

The cytoplasm is the portion of the cell outside the nucleus

It contains the organelles and is where some cellular processes take place

Nucleus

Contains nearly all of the cell’s DNA and instructions for making proteins & other molecules

It is surrounded by a nuclear envelope, which is made up of 2 membranes

Contains 1000’s of tiny pores which allow material (RNA & proteins) to move into and out of nucleus

Nucleus contains chromatin, which is DNA bound to proteins

Condenses to form chromosomes during cell division

May also contain a nucleolus, which is where ribosomes are made

Ribosomes

Site where proteins are assembled

Composed of RNA & proteins

Found in the cytoplasm or on other organelles

Produce proteins based on coded instructions from the nucleus

Endoplasmic Reticulum (ER)

It is an internal membrane system that synthesizes and exports materials

Site where lipid components of the cell membrane are assembled

Exports proteins and other material for the cell

There are 2 types of ER: smooth and rough

Rough ER is involved in protein synthesisContains ribosomes on its surfaceProteins leave ribosomes and enter ER

to be modified

Smooth ER lacks ribosomesContains enzymes the synthesize lipid membranes & detoxify drugsLarge amounts are found in liver

Golgi Apparatus

Named after Italian scientist Camillo Golgi

Accepts proteins modified in the rough ER

Function is to modify, sort, and package proteins & other materials from the ER

Lysosomes

Small organelles filled with enzymes that act like “clean-up crew” in the cell

Functions to digest, or breakdown lipids, carbohydrates, and proteins into small molecules

Breaks down old & worn out organelles

Vacuoles

Saclike structure that stores cellular materials like water, salts, proteins and carbs

Plants contain a large vacuole filled with water, which enables plants to support the weight of flowers and leaves

Single-celled organisms contain a contractile vacuole,

Used to pump out excess water from cell

Helps to maintain homeostasis

Mitochondria & Chloroplasts

Mitochondria are found in plant & animal cells

Functions as the cell’s “powerhouse” by converting energy stored in glucose to the cellular energy ATP

Composed of 2 membranes: inner & outer

The inner membrane is folded to increase surface area

Chloroplasts are found in plant cells and in a few other organisms

Contains chlorophyll, which is used to capture the energy during photosynthesis

Also composed of 2 membranes

Organelle DNA

Chloroplasts and mitochondria contain their own DNA

Biologist Lynn Margulis believes they are descendents from prokaryotic cells

Developed from symbiotic relationships

Cytoskeleton

Functions as support structure for cell

Consists of a network of protein filaments that help the cell maintain its shape

Two types of protein filaments: microfilaments and microtubules

Microfilaments are made of actin and their assembly and disassembly allow cytoplasmic movement

Microtubules are hollow structures made of tubulin

They are important in cell reproduction because they form the mitotic spindle which separates chromosomes

They are also responsible for the formation of cilia and flagella, which allow some cells to move

Centrioles are also made of tubulin and help to organize cell division