Anatomy of Cells Introduction to Biology The Discovery

Anatomy of Cells Introduction to Biology

The Discovery of Cells • In Holland, Anton van Leeuwenhoek examined pond water and a sample taken from a human mouth. • He drew the organisms he saw—which today we call bacteria. • Leeuwenhoek examined as many types of cells as he could. He even observed his own semen!

Overview: The Importance of Cells • The early discoveries of cells are summarized in the cell theory, a fundamental concept of biology. • The cell theory states: o All living things are made up of cells. o Cells are the basic units of structure and function in living things. o New cells are produced from existing cells.

Origin of Cellular Life • The Earth formed about 4. 6 billion years ago. o For about 500 million years, the Earth was continually bombarded by chunks of rock and ice in the solar system. • The early atmosphere of Earth contained: o o o Water vapor H 2 O Nitrogen N 2 Carbon dioxide CO 2 Methane CH 4 Ammonia NH 3

Origin of Cellular Life • How did life arise from such a harsh environment? • Two scientists designed a model of what conditions were like on Earth at this time. o This is called the Miller-Urey Apparatus

Miller-Urey Apparatus • This apparatus simulated three important conditions on Earth: – The high amount of lightning – Heat and gases released by volcanic activity – Water vapor present in the atmosphere.

Results of Miller-Urey Apparatus • Simple compounds including water (H 2 O), methane (CH 4), ammonia (NH 3), and hydrogen (H 2) were used to simulate the atmosphere. • After 2 weeks, 10 -15% of the carbon had been used to form sugars, amino acids, and parts of nucleic acids. o These simple organic compounds could have produced the proteins, lipids, and carbohydrates that make up life today.

The First Cells • The first life forms on Earth were likely single-celled prokaryotic organisms. o Prokaryotic organisms are single-celled organisms that do not have a nucleus. • Their DNA or RNA is usually floating freely inside the cell. o Prokaryotic cells also do not have any membrane bound organelles.

Pili Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0. 5 µm Flagella A typical rod-shaped bacterium A thin section through the bacterium Bacillus coagulans (TEM)

Parts of a Prokaryotic Cell • Nucleoid – Area where DNA or RNA is located. Not enclosed in a membrane like a nucleus. • Ribosomes – Small structures that use DNA or RNA instructions to produce proteins. • Pili – Hollow, hair-like structures that can be used to exchange genes. • Flagella – Spin to produce movement. • Cell membrane – Controls what leaves or enters the cell

Eukaryotic Cells • Eukaryotes are organisms with much larger and more complex cells than prokaryotes. • DNA is in a nucleus that is bounded by a nuclear membrane. • Have membrane-bound organelles • The largest eukaryotic cells are 0. 1 mm to 1. 0 mm in size. Why haven’t they evolved any larger?

LE 6 -7 Surface area increases while Total volume remains constant • Volume represents the size of the cell. • Surface area represents the amount of cell membrane to transport food, waste, water, 5 and oxygen. 1 Total surface area Total volume Surface-to-volume ratio 1

LE 6 -7 • A cell with a volume of 1 mm 3 will have a total surface area of 6 mm 2. • This provides plenty of area for the cell to absorb what it needs. 1 Total surface area (height x width x number of sides x number of boxes) 6 Total volume (height x width x length X number of boxes) 1 Surface-to-volume ratio (surface area volume) 6 Surface area increases while Total volume remains constant 5 1

LE 6 -7 • A larger cell with a volume of 125 mm 3 will only have a surface area of 150 mm 2. • This cell will not be able to transport wastes and nutrients fast enough. Surface area increases while Total volume remains constant 5 1 1 Total surface area (height x width x number of sides x number of boxes) 150 Total volume (height x width x length X number of boxes) 125 Surface-to-volume ratio (surface area volume) 1. 2

LE 6 -7 • If the larger cell is instead broken down into 125 smaller cells, it will once again have enough surface area. • This is why multicellular organisms exist! Surface area increases while Total volume remains constant 5 1 1 Total surface area (height x width x number of sides x number of boxes) 6 150 750 Total volume (height x width x length X number of boxes) 1 125 6 1. 2 6 Surface-to-volume ratio (surface area volume)

Cell Organization • The eukaryotic cell can be divided into two major parts: the nucleus and the cytoplasm. • The cytoplasm is the fluid portion of the cell outside the nucleus. • Prokaryotic cells have cytoplasm as well, even though they do not have a nucleus.

Eukaryotic Cell Anatomy • A eukaryotic cell has internal membranes that partition the cell into organelles. o Organelles are small structures within cells that have specific jobs. • Plant and animal cells have most of the same organelles, although there a few differences.

ENDOPLASMIC RETICULUM (ER Flagellum Rough ER Nuclear envelope Smooth ER NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes: Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm)

LE 6 -9 b Nuclear envelope NUCLEUS Nucleolus Chromatin Centrosome Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules CYTOSKELETON Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata

The Nucleus • The nucleus contains most of the cell’s genes and is usually the largest organelle. • The nuclear envelope is a membrane that encloses the nucleus, separating it from the cytoplasm. • In the same way that the main office controls a large factory, the nucleus is the control center of the cell. • The nucleus contains nearly all the cell’s DNA and, with it, the coded instructions for making proteins and other important molecules.

The Nuclear Membrane • The nuclear envelope is dotted with thousands of nuclear pores, which allow material to move into and out of the nucleus. • The nucleus mainly contains chromatin— the cell’s DNA instructions joined with proteins.

The Nuclear Membrane • The nucleus also contains a small dense region called the nucleolus. • The nucleolus produces ribosomes, which are needed to build proteins.

Organelles that Build Proteins • Because proteins carry out so many of the essential functions of living things, a big part of the cell is devoted producing and transporting them. • Proteins are synthesized on ribosomes, which can be found in two places: o Freely floating in the cytoplasm o Attached to the endoplasmic reticulum

Ribosomes: Protein Factories • Ribosomes are particles made of RNA and protein o Ribosomes produce proteins by following coded instructions that come from DNA. o Each ribosome is like a small machine in a factory, turning out proteins on orders that come from its DNA “boss. ”

Endoplasmic Reticulum • The endoplasmic reticulum (ER) is a huge membrane that is connected to the nuclear membrane. • There are two distinct regions of ER: o Smooth ER, which lacks ribosomes o Rough ER, with ribosomes studding its surface

Smooth Endoplasmic Reticulum • The smooth endoplasmic reticulum: o o Synthesizes lipids Metabolizes carbohydrates Stores calcium Detoxifies poison • The smooth endoplasmic reticulum does not contain any ribosomes, so it is unable to synthesize proteins.

Rough Endoplasmic Reticulum • The rough ER o Holds ribosomes o Produces any proteins needed by the cell.

The Golgi Apparatus • The Golgi apparatus is a series of flattened membrane sacs in the cytoplasm. • Functions of the Golgi apparatus: o Modifies, sorts, and packages materials into transport vesicles for storage or transport out of the cell. o A typical path for a protein produced by the cell: o Rough ER → Golgi → Cell membrane → Released by cell

LE 6 -16 -1 Nucleus Rough ER Smooth ER Nuclear envelope

LE 6 -16 -2 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi

LE 6 -16 -3 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi Plasma membrane

Organelles that Store, Clean Up, and Support • These are organelles that help the cell maintain its shape, clean up wastes, and store material needed later. o Vacuoles o Lysosomes o Cytoskeleton

Vacuoles • Vesicles and vacuoles are membrane-bound sacs that store many materials. • Plant cells often have one large central vacuole. This fills with water, making the cell rigid. o When they are empty and dry, plants wilt!

Lysosomes • Lysosomes serve as the cell’s cleanup crew. • A lysosome is full of enzymes that can digest proteins, lipids, polysaccharides, and nucleic acids. o Can also breakdown old organelles so they can be re-used. Animation: Lysosome Formation

Cytoskeleton • The cytoskeleton is a network of protein filaments that give the cell shape. o Can also help transport materials across the cell. • Centrioles are part of the cytoskeleton that help move chromosomes during cell division.

Organelles that Capture and Release Energy • All life requires energy. • Organisms either can get their energy from sunlight via photosynthesis, or by eating other organisms via cell respiration. • Photosynthesis occurs in chloroplasts. • Cell respiration occurs in mitochondria.

Mitochondria • Mitochondria are the power plants of the cell. • They convert the chemical energy stored in food into smaller molecules for the cell to use. • Mitochondria have two membranes, outer and inner. • The inner membrane is folded up to increase the amount of surface area to do chemical reactions.

Chloroplasts • Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis • Chloroplasts are found in leaves and other green organs of plants and in algae

Plasma Membrane • The plasma membrane is a selective barrier. o Allows passage of oxygen, nutrients into the cell, and waste out of the cell. • The general structure of a biological membrane is a double layer of phospholipids o This allows the cell to control what goes in and out.

Cell Wall • The cell wall is made of cellulose and serves as support and protection for the cell. • Animals do not have cell walls, but plants, fungi, and algae do. • The cell wall is outside of the cell membrane.

Plants: Plasmodesmata • The cell wall is so thick that oxygen, nutrients, water, and waste cannot travel easily through. • Plasmodesmata are channels that perforate plant cell walls • Through plasmodesmata, water and other small molecules can enter the cell.

Animals: Tight Junctions, Desmosomes, and Gap Junctions • Although animal cells do not have cell walls, they also have special structures within their cell membranes. • At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid. o Example: Lining of small intestines • Desmosomes (anchoring junctions) fasten cells together into strong sheets o Example: Layers of outer skin cells • Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells o Example: Cardiac muscle cells

LE 6 -31 Tight junctions prevent fluid from moving across a layer of cells Tight junction 0. 5 µm Tight junction Intermediate filaments Desmosome Space between cells 1 µm Gap junctions Plasma membranes of adjacent cells Gap junction Extracellular matrix 0. 1 µm

The Cell: A Living Unit Greater Than the Sum of Its Parts • Cells rely on the integration of structures and organelles in order to function • For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane