Cell Structure and Function

Cell Size 1. 1–100µm 2. Why is there a limit to cell size? a. Surface-to-volume ratio b. Distance from surface to center

diameter of DNA double helix tallest trees adult human chicken egg frog embryo most eukaryotic cells mitochondrion Figure: 04-01 Title: Relative sizes. Caption: Dimensions commonly encountered in biology range from about 100 meters (the height of the tallest redwoods) through a few micrometers (the diameter of most cells) to a few nanometers (the diameter of many large molecules). most bacteria virus proteins diameter of DNA double helix atoms

Cell types Prokaryotic—no nucleus, circular DNA, ribosomes Eukaryotic—larger, nucleus, linear chromosomes, membranous organelles

Prokaryotic Cells Have no membrane-bound organelles Include true bacteria On earth 3.8 million years Found nearly everywhere Spores in each breath; intestines Naturally in soil, air, hot springs

nucleoid (DNA) ribosomes food granule cytoplasm cell wall prokaryotic flagellum Figure: 04-10 Title: A generalized prokaryotic cell. Caption: plasma membrane cytoplasm cell wall

Eukaryotic Cells Have numerous internal structures Various types & forms Plants, animals, fungi, protists Multicellular organisms

nuclear pore chromatin (DNA) nucleus nucleolus nuclear envelope flagellum intermediate filaments cytoplasm plasma membrane rough endoplasmic reticulum ribosome lysosome microtubules Figure: 04-02 Title: A generalized animal cell. Caption: smooth endoplasmic reticulum Golgi complex free ribosome vesicle mitochondrion vesicle

(part of cytoskeleton) microtubules (part of cytoskeleton) mitochondrion chloroplast Golgi complex central vacuole smooth endoplasmic reticulum vesicle cell wall rough endoplasmic reticulum plasma membrane Figure: 04-03 Title: A generalized plant cell. Caption: nucleolus nuclear pore nucleus chromatin nuclear envelope intermediate filaments ribosomes free ribosome

Eukaryotic Cell Structure Cytoplasm is the clear, gelatinous fluid inside of a cell

Eukaryotic cell structure Nucleus is control center of the cell 1. Membrane bound (nuclear envelope) 2. Contains nucleoli; synthesizes ribosomal RNA 3. DNA in chromosomes (DNA and proteins)

nuclear envelope nucleolus nuclear pores chromatin Figure: 04-04a Title: The nucleus. Caption: (a) The nucleus is bounded by a nuclear envelope. Inside are chromatin (DNA and associated proteins) and a nucleolus. chromatin

nucleus nuclear pores Figure: 04-04b Title: The nucleus. Caption: (b) An electron micrograph of a yeast cell that was frozen and broken open to reveal its internal structures. The large nucleus, with nuclear pores penetrating its nuclear envelope, is clearly visible.

chromatin chromosome Figure: 04-05 Title: Chromosomes. Caption: Chromosomes, seen here in a light micrograph of a dividing cell (on the right) in an onion root tip, are the same material (DNA and proteins) as the chromatin seen in nondividing cells adjacent to it, but in a more compact state. chromosome

Eukaryotic cell structure Organelles Endoplasmic reticulum consists of folded membranes attached to the nucleus Rough ER is site of protein synthesis and protein secretion

rough endoplasmic reticulum smooth endoplasmic reticulum ribosomes 0.5 micrometers smooth endoplasmic reticulum Figure: 04-07 Title: Endoplasmic reticulum. Caption: There are two types of endoplasmic reticulum: rough ER, coated with ribosomes, and smooth ER, without ribosomes. Although in electron micrographs the ER looks like a series of tubes and sacs, it is actually a maze of folded sheets and interlocking channels. 0.5 micrometers vesicles

Eukaryotic Cell Structure Organelles (cont.) Ribosomes assemble amino acid into polypeptide chains a. Associated with the ER b. Composed of RNA and proteins

rough endoplasmic reticulum ribosomes Figure: 04-07R-1 Title: Rough endoplasmic reticulum. Caption: rough endoplasmic reticulum 0.5 micrometers

smooth endoplasmic reticulum vesicles Figure: 04-07R-2 Title: Smooth endoplasmic reticulum. Caption: smooth endoplasmic reticulum 0.5 micrometers

Eukaryotic Cell Structure Organelles (cont.) Golgi apparatus are membranous sacs associated with ER a. Processing and transport of proteins, lipids b. Synthesis and transport of polysaccharides

vesicles from ER vesicles leaving Golgi complex Golgi complex Figure: 04-08 Title: The Golgi complex. Caption: The Golgi complex is a stack of flat membranous sacs. Vesicles transport material from the ER to the Golgi (and vice versa) and from the Golgi to plasma membrane, lysosomes, and vesicles. Departing vesicles bud off from the Golgi on one face; arriving vesicles join it on the opposite face.

Eukaryotic Cell Structure Vacuoles: membrane-bound compartments that are temporary storage of materials Animal cells do not usually contain vacuoles, if they do they are very small Plant cells usually use them for water storage

Eukaryotic cell structure Organelles (cont.) Lysosomes are Golgi-derived vesicles containing digestive enzymes Digest excess or worn out organelles, food particles, and engulfed viruses or bacteria

vesicles from ER vesicles leaving Golgi complex Golgi complex Figure: 04-08 Title: The Golgi complex. Caption: The Golgi complex is a stack of flat membranous sacs. Vesicles transport material from the ER to the Golgi (and vice versa) and from the Golgi to plasma membrane, lysosomes, and vesicles. Departing vesicles bud off from the Golgi on one face; arriving vesicles join it on the opposite face.

Eukaryotic Cells: Organelles Energy sources for cell activities Mitochondria provide energy for cellular functions (respiration) a. Membrane bound, numerous b. Matrix/cristae c. Have their own DNA and ribosomes; self-replicate

5 micrometers Figure: 04-E4-2d Title: An SEM photo. Caption: (d) An SEM photo at much higher magnification, showing mitochondria, many of which are sliced open. 5 micrometers

Eukaryotic Cells: Organelles Energy sources for cell activities Chloroplasts—function in photosynthesis 1) Green—contain chlorophyll pigment 2) Stroma/grana (thylakoid stacks) 3) Have their own DNA and ribosomes; self-replicate 4) Up to 100 per cell

Eukaryotic Cells: Organelles Cytoskeleton Internal infrastructure Surface structures extensions of the plasma membrane aid in movement of simple organisms

actin subunits subunit tubulin subunit Figure: 04-2 Title: Cytoskeleton components. Caption: tubulin subunit

Cytoskeleton Microtubules-thin hollow cylinders made of protein Microfilaments- smaller, solid protein fibers They work together to maintain the shape of the cell

Centrioles Organelles found in the cells of animals and most protists Occur in pairs and are made up of microtubules Play an important role in cell division

Cilia and Flagella Cilia are short, numerous projections that look like hairs Flagella are longer projections that move with a whip-like motion Both are used for locomotion or feeding

Prokaryotes & Eukaryotes Similarities & differences Both surrounded by plasma membrane, but very different Prokaryotes – Archaebacteria and Eubacteria Eukaryotes – everything else

Plant & Animal Cells Similarities Both constructed from eukaryotic cells Both contain similar organelles Both surrounded by cell membrane

Plant & Animal Cells Differences Animals have Plants have Cell wall – provides strength & rigidity Have chloroplasts, photosynthetic Animals have Other organelle not found in plants (lysosomes formed from Golgi) Centrioles, important in cell division

Brief Look at Viruses Viruses are acellular Not considered to be living Cause serious diseases in most organisms