Unit 4 Cellular Biology

Textbook Chapter 7Review Book Topic 1

What is a Cell? All living things are made of cells

Basic structural and functional unit of living things

Can be composed of a single cell (unicellular) or multiple cells (multicellular)

Cells carry on all life processes of an organism

Organization of Living Things

In multicellular organisms Groups of specialized cells form tissues

Different kinds of tissues are combined to form organs which carry out life processes

Each organ is part of an organ system which transports materials throughout the body

History of Cellular Biology Robert Hooke (mid-1600s)

Examined thin pieces of cork

Observed boxlike structures of the dead walls of a plant cell

Called these boxes: “cells”

Never studied living cells

Anton van Leewenhoek (mid-1600s) Observed pond water

Saw microorganisms within the water samples

Observed and described human blood cells

Described bacteria

Robert Brown (early 1800s) Observed small, dense, round bodies which

appeared in all plant cells

Called the structure the “nucleus”

Cell Theory All organisms are made up of one or more

cells

All cells carry on life activities

The combined activity of individual cells make up the life activities of a multicellular organisms

New cells arise from pre-existing cells

Cell Types

Prokaryotic vs. Eukaryotic

Prokaryotic Organisms Lack internal membrane-bound organelles

Prokaryotic = “Without nucleus”

1-10 µm (micrometers) – very small

Ex. Archaebacteria and Eubacteria

Cell Characteristics Lack a membrane bound nucleus, but instead

have a single, circular chromosome found in a region called a nucleiod

Contains: Cell wall Plasma membrane Capsule – secretion of a slime-like material to give added

protection to the cell

Characteristics Continued Most life processes occur on the surface of the

plasma membrane

Ribosomes located throughout cytoplasm (protein synthesis)

May use cilia or flagella for movement

Pili are sexual appendages used in conjugation (reproduction)

Eukaryotic Cell Internal membrane bound organelles

Eukaryotic = “True nucleus”

10-100 µm (micrometers) – larger than bacteria Largest single cell can be seen in bird eggs (ex. ostrich)

Ex. Animals, plants, protists, fungi

Similarities

Similarities Membrane which separates internal components

from the external environment

Contain genetic material

Contain ribosomes to make proteins

Suspend materials in cytoplasm

Carry out the same life processes

Animal Cell

Plant Cell

Organelles Plasma membrane Cell wall (PLANTS ONLY) Nucleus Cytoplasm Endoplasmic Reticulum Ribosomes Golgi Complex

Organelles Continued Lysosomes Mitochondria Chloroplasts (PLANTS ONLY) Microtubules/microfilaments Centrioles Cilia/flagella Vacuoles

Cell Wall Included in all plants and most bacteria

Lies outside of plasma membrane

Gives cell its shape and provides protection

Plants have cell walls made of cellulose (source of fiber in our diets!)

Has small openings to allow materials to pass to and from the cell membrane

ANIMAL CELLS DO NOT HAVE CELL WALLS

This is what Hooke observed in the mid-1600s with his microscope when observing cork cells

Plasma Membrane

Function Separates the cell from its surrounding

environment

Controls movement of materials into and out of the cell (selectively permeable)

Keeps internal conditions of the cell constant by maintaining homeostasis

Function Continued Signaling mechanism

Used for making energy for the cell

Used for cell to cell recognition

Used to compartmentalize organelles

Structure Two Layers (bi-layer)

Composed of: Lipids Proteins Carbohydrates Cholesterol

“Fluid-like” – called the fluid mosaic model

Phospholipids Composed of:

Two fatty acid chains

Phosphate group

Glycerol backbone

Hydrophobic (non-polar) region “Hates” water Most important factor in the formation of

membranes Fatty acid chain components

Hydrophilic (polar) region “Loves” water Phosphate and glycerol components

Proteins Can be found:

On the outer surface of membrane (glycoprotein)

On the inner surface of membrane (peripheral)

Extending through the membrane (trans-membrane or integral)

Proteins Continued Function:

Controls movement of substances through the membrane (transport)

Acts as a receptor to signaling the cell to start or stop a metabolic activity (communication)

Helps connect neighboring cells to each other or structural elements inside the cell (structure)

Carbohydrates Linked to membrane proteins or lipids

(glycoproteins or glycolipids)

Branching from external surface of the membrane ONLY

Used in cell recognition and signaling

Cholesterol Has hydrophobic and hydrophilic regions

Helps prevent membranes from being too “fluid-like”

Without cholesterol, cell membranes wouldn’t be firm enough and would be too permeable to some molecules

Nucleus Round, membrane-bound structure in

Eukaryotic cells

Serves as the control center for cell metabolism and reproduction

Largest organelle

Nucleus Continued Enclosed by the nuclear envelope

Membrane surrounding the nucleus

Double membrane

Contains selectively permeable pores

Nucleus Continued Contains chromatin

DNA bound to various proteins

Long, thin strands

Make up chromosomes (hereditary material) by coiling tightly during cell division

Nucleus Continued Within the nucleus is

a nucleolus

Dense, solid structure

Site of ribosome production

Cytoplasm Watery material within cell

Contains dissolved materials for cell metabolism

Chemical reactions in the cell occur here (metabolism)

Cytoplasm Continued All organelles are suspended in this

material

Endoplasmic Reticulum System of fluid-filled canals

Paths for the transport of materials throughout the cell

Highly folded to increase the surface area for chemical reactions to occur

Endoplasmic Reticulum Continued

Can be connected to the nuclear envelope or free floating in the cytoplasm

Rough ER Ribosomes are attached to the outer surface

Smooth ER No ribosomes

Ribosomes Site of protein synthesis

Found attached to the endoplasmic reticulum (rough ER) or in cytoplasm (free ribosomes)

Golgi Complex Stacks of flattened membrane sacs

Processes, packages and stores products being released from the cell

Animal cells usually have only one, located near the nucleus

Plant cells have several hundred (remember...they are the main producers in our food chain ! )

Golgi Complex Continued Example:

Proteins are produced by ribosomes on the rough ER

These proteins are transported by the ER to the golgi

Golgi process and package the proteins into vesicles

Protein is transported to where it is needed in the cell, stored or sent to the plasma membrane to be sent out of the cell

Lysosomes Small, bubble-like structures surrounded by a single

membrane (vesicle) Contain no water…so this allows it to have a

single membrane

Contains strong digestive acids

In single-celled organisms: Involved in the digestion of food within the cell

Lysosomes Continued In multicellular organisms:

Breaks down worn-out cell organelles

Part of the body’s defense against disease Ex. White blood cells

Involved in developmental processes Ex. Tadpole frog, digestion of its tail

Vacuoles Fluid filled organelles enclosed by a membrane

Plant cells contain a single, large vacuole which occupies most of the space within a cell

Used as a storage site (remember plants are producers and need to store all that energy in the form of sugar ! )

Vacuoles Continued Animal cells:

Very small and few in number

Excess water is collected in contractile vacuoles (shaped like a star or sun)

Mitochondria Round or oval shaped

Releases energy in food molecules for cell use

By the process of cellular respiration

“Powerhouse” of the cell

Usually 300-800 per cell depending on cellular activity

Mitochondria Continued Cells requiring lots of energy contain large numbers of

mitochondria

Ex. Muscle cells, heart cells

Capable of moving independently throughout the cell

Contain their own DNA and are capable of duplicating themselves

Surrounded by a double membrane Inner membrane is highly folded, forming

cristae that extend into the middle of organelle

Cristae provide a large surface area where biochemical reactions can occur

Mitochondria Continued

Plastids Membrane-enclosed organelles that are found only

in photosynthetic, eukaryotic organisms

ONLY IN PLANT CELLS (and some algae)

Two types: Leucoplasts – colorless pigments Chromoplasts – colored pigments

Most important is the chloroplast (green)

Chloroplasts Plastid containing a green pigment called

chlorophyll

Site of photosynthesis Food making process which uses light energy (autotrophic

nutrition carried out by producers)

Contains stacks of photosynthetic membranes called grana which contain chlorophyll

Chloroplasts Continued

Watery material that fills the remainder of the chloroplast is known as the stroma

Contain their own DNA and have the ability to duplicate themselves

Microtubules Long, hallow, cylindrical structures found in the

cytoplasm (made of protein)

“Skeleton” for the cell, giving it its shape

Used during cell division

Found in: Centrioles Cilia Flagella

Cilia & Flagella Hair-like organelles with the capacity for movement

Single-celled organisms – cell movement Multicellular organisms – used to move

substances over the cell’s surface

Extends from the surface of cells

Structures are identical but flagella are longer and fewer in number than cilia

Centrioles Found near the nucleus in animal cells

Pair of cylindrical microtubules which lie at a right angle (90º) to each other

Involved in cell division in animals cells

Microfilaments Long, solid, threadlike strands made of protein

Associated with cell movement Ability to contract (ex. muscle cells)

Involved in cytoplasm movement (ex. cytoplasmic streaming in ameoba)

Serve as supporting structures for the cell

Origins of the Eukaryotic Cell

The structural differences between eukaryotic and prokaryotic cells are so great, biologists have wondered how these two kinds of cells are related

Most ideas are based on evidence that has been collected, called the endosymbiotic theory

Eukaryotic cells are the result of:

Endosymbiosis – condition in which one organism lives inside the cell of another organism to the benefit of both (mutualism)

Mitochondria and chloroplasts are thought to be the result of bacteria which were engulfed by, then lived within, other larger cells

Evidence – both contain their own DNA and can reproduce themselves like bacteria, similar in size to bacteria, have same metabolic machinery as bacteria