cell form and function

Cell Form and Function

Dr. AndersonGCIT

Cell Diversity • Connect tissues and transportation – blood, epithelia

• Body movement – muscles (smooth, striated, cardiac)

• Storage – adipose (fat cells), hepatocytes

• Immune Function – WBC’s

• Communication and information processing – nerve cells

• Reproduction – Egg and sperm cells

Cell Membrane • Keeps the cell contents separate from the

environment (extracellular fluid)

The Fluid Mosaic Model• Cell membrane is made of a phospholipid

bilayer– Self-assembling!– Extremely thin

Non-polar tails

Polar Heads

Polar Heads

Polar Heads are phospholipids and the non-polar (hydrophobic) ends are fatty acids

Outside of cell – interstitial fluid

Inside of cell – cytoplasm

Membrane ProteinsFacilitate the transport of material across the membrane

Integral (trans-membrane) protein – facilitates transport into and out of the cell

Membrane Proteins

Peripheral protein – can be attached to inside or outside layer of cell membrane

• Act as enzymes (outside and inside) or serve to move or support the cell (inside)

Glycoproteins – sugar-bound proteins

Glycoproteins – make up a sugary coat that envelops the cells called the glyco-calyx or “sugar cup”

The Glycocalyx

• The carbohydrates on the cell surface provide a way for some cells to recognize each other– Sperm and egg– WBC and bacteria or other pathogens

Membrane Junctions

• Bind cells together – glycoproteins act as adhesive

• Cell membrane structure – tongue-and-groove

• Specialized Junctions – – Tight junction– Desmosomes– Gap Junctions

Special Membrane Junctions• Tight Junctions – proteins in the cell membranes

that bind cells together– Makes sure nothing passes between cells

• Desmosomes - small points of connective proteins that anchor cells together– Found in cells subject to heavy pulling forces

• Gap Junctions – an open junction between adjacent cells– Permits chemical communication (transport) between

cells

Membrane Transport

• Interstitial Fluid – extracellular fluid largely derived from blood, but acellular– Amino acids, wastes, electrolytes, sugars, etc.

• Cells need to hold a balance of these solutes between their inside and outside environments

• How is this done?

Membrane Permeability

• Membranes only allow passage to certain molecules, or only permit movement in one direction

• Selectively Permeable – only certain molecules can pass

Active Transport

• ATP is used to drive the concentration gradient across the cell membrane 1. Primary – ATP changes the shape of membrane

proteins to shuttle specific materials across2. Secondary - uses stored potential energy from

primary transport to move substances3. Vesicular – vesicles “gulp” materials from outside

the cell by pinching off a bubble from the cell membrane

ELMO

• Review Pages 74-75 in textbook to explain prior slide in more detail

Vesicular Transport

• Endocytosis – cell ingests materials via vesicles– Receptor mediated

• Exocytosis – cell expels material into the environment via vesicles

• Phagocytosis?

Plasma Membrane – Resting Potential

• Many cells work using electrical energy which is derived from ion separation– Muscle cells, nerve cells, etc.

• How is this accomplished?

Electric Membrane Potential

- --

- --

- - ---

+ ++

K+

++

++ ++

Anions (negatively charged proteins build up)

K+

pump

Cations (postively charged ions (K, Na) build up)

Cytoplasm

• The material between the cell membrane and the nucleus

• Three major elements– Cytosol– Organelles– Inclusions

Cytosol

• Liquid part of the cytoplasm

• Consists of mostly water, but also dissolved substances such as– Salts– Sugars – proteins,– Etc.

Cytoplasmic Organelles

• Carry out cellular metabolic processes

• Specific to the kingdom of living things (e.g. chloroplasts are only found in plants)

Mitochondria

• Powerplants of the cell

• Breaks down food and uses this energy to form ATP from ADP (cellular respiration)on inner membranes (cristae)

• Have their own DNA, RNA and ribosomes– Huh?

Ribosomes• Made of two RNA-protein

subunits that work together to synthesize proteins (protein translation)

• Two types– Free ribosomes – make

soluble proteins– Membrane-bound

organelles – make proteins for packaging or export

Endoplasmic Reticulum (ER) • Membranes in the cytosol that are

continuous with the nuclear membrane

• Rough ER – lined with ribosomes that produce proteins that are secreted from cells, also make new phospholipids and intracellular membranes

• Smooth ER – Embedded with enzymes that catalyze the metabolism of proteins, fats, hormones, toxins and glycogen

Golgi Apparatus

• Stacks of membranous sacs in the cytosol

• Used to concentrate, modify and/or package proteins and lipids made by the rough ER.

• Packaged proteins are called vesicles are sent into the cytosol or outside of the cell (exocytosis)

Lysosomes

• Contain activated enzymes that may be capable of digesting all type of biological molecules

• The membrane-bound lysosomes contain these dangerous substances, preventing cell damage

Peroxisomes

• Contain extremely reactive oxygen species (ROS) that are used to detoxify certain poisons such as alcohol

• Also destroy free radicals – highly reactive waste products of metabolism that can disrupt cell processes– In which cells might these be found?

Cytoskeleton

• Consists of rods made of tubulin that run through the entire interior of the cell– Microtubules– Microfilaments– Intermediate

filaments

Cytoskeleton Components• Microtubules– Determine cell shape and influence organelle dstribution

• Microfilaments – A “web” of these filaments attach to the inner surface of

the cell membrane and give the cell strength. Also helps change cell shape during mitosis/meiosis

• Intermediate Filaments– Give the cell tensile strength by attaching to desmosomes

Centrosomes and Centrioles

• Centrosomes – serve to anchor microtubules and provide attachment points during activities such as cytokinesis, alignment of chromosomes during mitosis (mitotic spindle)

Cilia

• Relatively short extensions of tubulin that cover cells

• Enables cells to move through their environment, or move the liquid environment around themselves

Flagella

• Long extensions of tubulin protein used for propulsion

• Many microorganisms possess flagella

• Only human cells that possess flagella are sperm cells

Inclusions

• Chemical substances that may or may not be present, depending on the cell type. – Pigments– Crystals– Vacuoles– Etc.

The Nucleus

• The nucleus is a membrane-bound organelle that serves as the central control system of the cell

• All instructions for the cell’s processes are carried on genes that can be found within the DNA housed inside the nucleus

Nucleus

• Nuclear Envelope – double layered membrane that surrounds the nucleus– Outer Layer – continuous with ER– Inner Layer – lined with lamina, filaments that

hold the nuclear shape– Nuclear pores penetrate both layers, allowing

some molecules to flow into and out of the nucleus

Nucleus

• Nucleoli – dark-staining regions in the nucleus where ribosomal RNA (rRNA) is made

• Chromatin – DNA wound around protein units called histones– This form of DNA allows

efficient packing and storage of DNA (a nucleosome) during periods where the cell is not actively dividing

Nucleus - Chromosomes

• During cell division, chromatin winds up to form bar-shaped structures called chromosomes

• The arrangement of these structures allows the definition of different stages of cell division

Human Karyotype

• Chromosome sizes and number can also be used to screen for genetic diseases

DNA Replication

Helicase

DNA Polymerase

DNA Polymerase