Cell Structure

Analysis of the functional inter-relationships of cell structures

Cell Biology: the study of cells – the structural and function units of all living organisms

morphologically cells vary in shape and size

bacteria

red blood cells

white blood cells

platelets nerve cell

human sperm cells

cancer cells (myeloma)

portion of skeletal muscle cells

cells also vary physiologically

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Cell Theory

1. Cells are the basic unit of life

2. All organisms are made of one or more cells

3. Cells come from pre-existing cells

Cells Tissues Organs

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Nucleus and Nucleoid

a nucleoid (which consists of the organisms DNA) is NOT enclosed in a membrane = prokaryotic cell

eukaryotic cell = DNA contained within a membrane

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Eukaryotic Cells

• Bounded by cell membrane

• Cytoplasm inside cells composed of aqueous solution, organelles and molecules

• Various fibres compose a cytoskeleton to give shape and structure

Nucleus• Contains genetic material which

controls/directs the activities of the cell• function: “brain” of cell, i.e. determines

metabolism, growth, differentiation, & reproduction of cell

• Nucleus enclosed in a nuclear envelope• Within nuclear envelope is

chromosome/chromatin, nucleoplasm and nucleoli

• Chromosomes/chromatin are long strands of DNA wrapped around protein molecules which make up genes (units of heredity)

• nucleoplasm is a highly viscous liquid • Nucleoli is the site where rRNA is

assembled (rRNA then travels to the cytoplasm for protein syntheis)

DNA packed in Chromosomes

Chromatin vs. Chromosome

Ribosome• consist of 2 non–

identical subunits formed from rRNA & proteins

• function: protein synthesis

• found attached to endoplasmic reticulum or free in cytoplasm

• polysome: group of ribosomes simultaneously synthesizing same protein

Membranous Canals

• Includes endoplasmic reticulum, golgi apparatus, vacuoles and lysosomes

Endoplasmic Reticulum• Series of membranous canals exist in

cytoplasm• Can extend from nuclear envelope to

cell membrane• rough endoplasmic reticulum:

– ribosomes attached to surface– function: synthesize proteins for

secretionNOTE: unlike free ribosomes that synthesize proteins for use within cell

• smooth endoplasmic reticulum:– no ribosomes attached to surface– functions:1. synthesis of lipids, e.g. cell membrane

& hormones2. metabolism of carbohydrates, e.g.

synthesis of glycogen3. detoxify drugs & wastes in cell, e.g.

alcohol

Golgi Apparatus

• resembles flattened stack of hollow tubes,i.e. similar to smooth endoplasmic reticulum, but closer to cell membrane

• function: sorting, modification (assembly), & packaging of substances for storage or secretion

e.g. produces glycolipids by joining carbohydrates to lipids

• receives vesicles from endoplasmic reticulum that contain newly synthesized proteins/lipids proteins/lipids sorted, modified, & packaged into new vesicles that bud offvesicles transported within cell or moved to cell membrane for export by exocytosis

Vacuoles

• large, membrane enclosed sac• vesicle: small vacuole• functions: storage or transport• formed by:

1. budding off (pinching off) from Golgi apparatus

2. endocytosis of cell membrane

3. extension of endoplasmic reticulum membrane

Lysosomes

• vesicle formed by Golgi apparatus, which contains hydrolytic enzymes

• functions:1. cellular digestion of food

particles, i.e. fuses with food vacuoles & enzymatically digests proteins, carbohydrates, & lipids

2. disposal of damaged cell organelles, e.g. mitochondria

3. breakdown of whole cell, i.e. releases contents into cell cytoplasm

Energy related organelles

Mitochondria

• function: cellular respiration (aerobic metabolism), i.e. converts glucose (carbohydrates) to energy (ATP)

• chemical reaction:

C6H12O6 + 6O2 6CO2 + 6H2O + energy (ATP)• cristae (singular: crista): shelf–like structures formed from folded

inner membrane with enzymes on surface for cellular respiration– Provides lots of surface area for cell. resp. reaction.

• matrix: solution surrounded by cristae contains DNA

Choloroplast

• function: photosynthesis in plant cells, i.e. converts sunlight energy to carbohydrates

• Made up of membranous stacks called grana, which contain chlorophyll pigments

• chlorophyll: chemical that absorbs sunlight energy & allows photosynthesis to occur

Basic Photosynthesis

Works hand in hand with cellular respiration

Organelles made up of Membranes:

• Nuclear envelope• Endoplasmic reticulum• Golgi apparatus• Lysosomes• Vacuoles• Vesicles• Cell membrane• Mitochondria • Chloroplast

Note: Membranes are composed of phospholipids

Cell Shape

Other Organelles

• Cell wall: – rigid cellular layer that surrounds the cell membrane

in plant cells– Provides protection, shape, and support for the cell– Composed of cellulose

• Cytoskeleton– network of protein fibres– functions: maintain cell shape, anchor organelles, &

involved in motility

Characteristics of Living Things

• Living things are made of cells.

• Living things obtain and use energy.

• Living things grow, reproduce and repair.

• Living things produce waste.

• Living things respond to their environment.

• Living things have a life span.

By the end of this section you should be able to

• Prokaryotic cell verses a eukaryotic cell• Describe the following cell structures and their functions

– Cell membrane– Cell wall– Chloroplast– Cytoskeleton– Cytoplasm– Golgi bodies– Lysosomes– Mitochondria – including cristae and matrix– Nucleus - including nuclear pore, nucleolus, chromatin, nuclear envelope, and

chromosomes– Ribosomes (and polysomes)– Smooth and rough endoplasmic reticulum– Vacuoles– Vesicles

• State the balanced chemical equation for cellular respiration and photosynthesis• Describe how the following organelles function to compartmentalize the cell and more materials

through it:– Rough ER and smooth ER– Vesicles– Golgi bodies– Cell membrane

• Identify cell structures depicted in diagrams and electron micrographs