Cell Structures A Tour of the Cell Overview

Cell Structures A Tour of the Cell

Overview: The Fundamental Units of Life • All organisms are made of cells • Cell: collection of living matter enclosed by a barrier – Basic unit of all forms of life

Prokaryotic vs. Eukaryotic • The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic • Prokaryotic: bacteria • Eukaryotic: protists, fungi, animals, and plants

Comparing Prokaryotic and Eukaryotic Cells • Basic features of all cells: – Plasma (cell) membrane – Semifluid substance called cytoplasm (cytosol) – Chromosomes (carry genes) – Ribosomes (make proteins)

• Prokaryotic cells are characterized by: – A cell wall and cell membrane – No nucleus – Cytoplasm bound by the cell membrane – DNA in the cytoplasm – No membrane-enclosed organelles

• Eukaryotic cells are characterized by: – DNA in a nucleus bound by a membrane • The membrane is the nuclear membrane (envelope) – Membrane-bound organelles – Cytoplasm between the cell membrane and nucleus • Eukaryotic cells are generally much larger than prokaryotic cells

• The cell membrane is a phospholipid bilayer – It is a selective barrier • Only allows certain things into and out of the cell – Oxygen, nutrients, and waste

• A eukaryotic cell has internal membranes that separate the cell into organelles – Only plant cell organelles will be discussed – Organelle: specialized structure that performs important cellular functions

Cytoplasm (Cytosol) • Jelly-like fluid and materials containing everything between the cell membrane and nucleus • Including organelles • Where most of the cell’s work is done

The Nucleus • The nucleus is the control center of the cell – Usually the easiest organelle to see under the microscope – Contains most of the cell’s DNA • Instructions (blueprints) for making proteins and other molecules • The nuclear envelope encloses the nucleus, separating it from the cytoplasm – The nuclear membrane is a double membrane • Thousands of pores within the membrane allows for passage of materials in and out to receive messages and send instructions

• The nucleolus is the small dense (dark) area within the nucleus – Where ribosome production occurs • Ribosomes then move into the cytoplasm

Ribosomes • Ribosomes are made of RNA and protein • Ribosomes produce proteins in two areas: – In the cytoplasm (free ribosomes) – Attached to the outside of the endoplasmic reticulum (bound ribosomes) • Produce proteins by following instructions (orders) sent from the nucleus

The Endoplasmic Reticulum • The endoplasmic reticulum (ER) is an internal membrane system (made of membranes) • The ER membrane connects to the nuclear envelope • Used to produce and transport materials such as proteins • There are two distinct regions of the ER: – Smooth ER, which lacks ribosomes – Rough ER, with ribosomes on its surface

Functions of Rough ER • The rough ER – Has bound ribosomes • Proteins made (synthesized) in ribosomes are moved to the ER to be modified (changed or added to) – Then these proteins are released into the cell or exported out of the cell – Is a membrane factory for the cell • Makes many proteins found on the cell membrane

Functions of Smooth ER • The smooth ER – Synthesizes (produces) lipid components of the cell membrane • Sometimes stores lipids after making them – Detoxifies drugs • Makes poisons no longer poisonous (neutralizes)

The Golgi Apparatus • The Golgi apparatus is made of membranes – Look like flattened stacks of membranes • Functions of the Golgi apparatus: – Modifies, sorts, and packages products of the ER • Customizes proteins and other materials • Stores for later use • Packages and ships products outside the cell

Vacuoles • A plant cell may have one or more vacuoles • Vacuoles hold organic compounds (salts, proteins, and carbohydrates) as well as water for later use – Makes it possible for plants to support leaves and flowers (heavy structures)

Chloroplasts and Mitochondria • Chloroplasts and mitochondria – Have a double membrane • Two membranes make up the organelles – Have proteins made by free ribosomes – Contain their own DNA

Chloroplasts • Chloroplasts, found in plants and are the sites of photosynthesis – Captures energy from sunlight and converts it into chemical energy (food) – Solar power plant • Contain large stacks of membranes containing chlorophyll – Chlorophyll is the green pigment that function in photosynthesis by capturing light energy • Chloroplasts are found in leaves and other green organs of plants and in algae

Mitochondria • Mitochondria convert the chemical energy in food into compounds the cells can use – The site of cellular respiration, a metabolic process that produces ATP • ATP is the molecule cell’s use for energy (to do their work) • Mitochondria are in nearly all eukaryotic cells – Inherited from your mother through the egg (ovum)

Cell Walls of Plants • The cell wall is an extracellular structure that distinguishes plant cells from animal cells – Extracellular: outside the cell membrane • Also found in algae, fungi, and many prokaryotes • Porous (contains mini holes) to allow for water, oxygen, carbond dioxide, and small molecules to pass through • The cell wall in made within the cell itself

• The cell wall helps protect the plant cell by providing extra shape and support for the cell – Make up of cellulose • Cellulose is a carbohydrate polymer that strengthens the plant cell wall and only found in plants – Not the same thing as cellulite (found in animals) – Cellulose is the primary component of wood and paper – Prevents excessive uptake of water • What happens in animal cells when too much water is taken into the cell?

Lab • Wednesday – We will meet as normal to discuss the experiment • The experiment will explore how the plant’s cell wall helps maintain shape when under harsh conditions. • This experiment uses the microscope so review how to use the microscope from your notes of the first 9 weeks.