Chapter 4: Cell Structure

Why does the DNA, the enzymes , and other cytoplasmic constituents have access to all parts of the cell?

Because a prokaryotic cell contains no membrane-bounded organelles.

What is the role of microtubules in the cytoskeleton?

Microtubules (tubulin) act as a scaffold to determine cell shape, and provide a set of "tracks" for cell organelles and vesicles to move on

What are mitochondria?

Mitochondria are "tubular or sausage-shaped" organelles about the size of bacteria that are found in all types of eukaryotic cells.

What do lysosomes contain?

They contain high levels of degrading enzymes, which catalyze the rapid breakdown of proteins, nucleic acids, lipids, and carbohydrates.

In eukaryotes, what is the role of the endomembrane system?

"Endo" -> Greek for "within" The endomembrane system fills the cell, dividing it into compartments, channeling the passage of molecules through the interior of the cell, and providing surfaces for the synthesis of lipids and some proteins.

What are the 4 major features that all cells have in common?

1) A Nucleoid, or nucleus (Where genetic information is located) 2) A Cytoplasm (Composed of a semifluid matrix of organelles and cytosol) 3) Ribosomes (To synthesize proteins) 4) A Plasma membrane (Composed of a phospholipid bilayer)

What are the 4 components that are required to move material along microtubules?

1) A vesicle or organelle that is to be transported. 2) A motor protein that provides the energy-driven motion. 3) A connector molecule that connects the vesicle to the motor molecule. 4) Microtubules on which the vesicle will ride like a train on a rail.

"Just as a house cannot maintain its structure without nails and cement, so a tissue cannot maintain its characteristic architecture without the appropriate cell junctions..." What are the 3 types of junctions you find in animal cells?

1) Adhesive junctions 2) Septate, or tight junctions 3) Communicating / gap junctions

Explain cell theory.

1) All organisms are composed of one or more cells. 2) Cells are the smallest living things. 3) Cells arise only by division of a previously existing cell.

What are the 3 types of fibers that compose the cytoskeleton?

1) Microfilaments 2) Microtubules 3) Intermediate filaments

Compare the genetic material of prokaryotes and eukaryotes.

1) Prokaryotes: The genetic material lies in a single circular molecule of DNA, in the nucleoid 2) Eukaryotes: The genetic material is found in DNA in the nucleus, which is surrounded by a double membrane structure called the nuclear envelope.

What affects the rate of diffusion of substances in and out of cells?

1) Surface area available. 2) Temperature. 3) Concentration gradient of diffusing substance. 4) Distance over which the diffusion must occur.

Transport across the pore is controlled and consists mainly of the import and export of what?

1) The import of proteins that function in the nucleus 2) The export to the cytoplasm of RNA and RNA-protein complexes formed in the nucleus.

Which other types of ribosomes does the synthesis of proteins require? Other than rRNA...

1) mRNA, which carries coding information from DNA 2) tRNA, which carries amino acids.

Explain how mitochondria are created in cell division.

A eukaryotic cell does not produce brand-new mitochondria each time the cell divides. Instead, the mitochondria themselves divide in two, doubling in number, and these are partitioned between the new cells.

What is a leucoplast?

A leucoplast is a DNA-containing organells in plants. In root cells they may serve as starch-storage sites.

What is a peroxisome?

A peroxisome is a microbody which contains enzymes involved in the oxidation of fatty acids.

What are adhesive junctions? What is their composition? Give an example of adhesive junctions in vertebrates.

Adhesive junctions mechanically attach the cytoskeleton of a cell to the cytoskeletons of other cells or to the ECM. Adherens junctions are based on the protein cadherin, which is a Ca²⁺-dependent adhesion molecule. Desmosomes are a cadherin-based junction unique to vertebrates. e.g. Some muscles tears involve the rupture of desomosomes.

What is a amyloplast?

An amyloplast is a leucoplast that stores starch.

Which domain of prokaryotic life lacks peptidoglycan?

Archae.

What are centrioles?

Barrel-shaped organelles found in the cells of animals and most protists.

What is the role of the cell wall?

Cell walls protect the cell, maintain its shape, and prevent excessive uptake or loss of water.

What is the hallmark of the eukaryotic cell?

Compartmentalization, through a combination of an extensive endomembrane system that weaves through the cell interior and by numerous organelles.

"All eukaryotic cells are supported by an internal protein scaffold called..."?

Cytoskeleton.

Where is DNA stored in eukaryotes?

DNA in eukaryotes is stored in the nucleus. The DNA is tightly wound around proteins and packaged into compact units called chromosomes.

What are thylakoids?

Each granum of the chloroplast can contain from few to several dozen disk-shaped structures called thylakoids. On their surface are the light capturing photosynthetic pigments.

"The outer membrane of the nuclear envelope is continuous with the cytoplasm's interior membrane called the..."?

Endoplasmic reticulum.

In general, what are the components of a prokaryote? (6)

Flagellum, Cell membrane, Cell wall, Cytoplasm, Ribosomes, and Nucleoid.

Describe what else comes in equation for mitochondria replication.

For mitochondria to replicate, there is the need of nuclear participation, because most of the components required for mitochondrial division are encoded by genes in the nucleus and are translated into proteins by cytoplasmic ribosomes.

Give 2 types of surface proteins.

Glycolipids and MHC proteins.

What is chromatin?

In eukaryotes, DNA is divided into multiple linear chromosomes, which are organized with proteins into a complex structure called chromatin.

"As the size of the cell increases, the length of time for diffusion from outside the membrane to the interior for the cell..."?

Increases.

What links the ECM and cytoskeleton in animal cells?

Integrins

What are integrins?

Integrins are an integral part of the plasma membrane, extending into the cytoplasm, where they are attached to the microfilaments and intermediate filaments of the cytoskeleton. Linking the ECM and the cytoskeleton, integrins allow the ECM to influence cell behavior in important ways.

What is the cytoplasm?

It is a aqueous medium, containing all the sugars, amino acids, and proteins the cell uses to carry its everyday activities.

What is the nucleolus? And what is it useful for?

It is a region of the nucleus, where intensive synthesis of ribosomal RNA takes place.

What is an organelle?

It is any discrete macro-molecular structure in the cytoplasm specialized for a particular function.

What do you call the cell-cell junctions in plants?

It is called plasmodesmata. They function much like gap junctions in animal cells, although their structure is more complex. Plasmodesmata are lined with plasma membrane and contain a central tubule that connects the endoplasmic reticulum of the 2 cells.

What is the stroma? What do we find in it?

It is the fluid matrix surrounding the thylakoid. In the stroma we can find the enzymes used to synthesize glucose during photosynthesis.

What are centrosomes? What is its role?

It is the region surrounding centrioles. Centrosomes are microtubules-organizing centers.

What is the role of the central vacuole?

It stores proteins, pigments and waste materials.

What is symbiosis?

It's a close relationship between organisms of different species that live together.

What is the cytosol?

It's the part of the cytoplasm that contains organic molecules and ions in solution.

What are the 2 types of microscopes?

Light and electron microscopes.

What are MHC proteins? What do they permit?

MHC proteins are surface proteins that permit the recognition of "self" and nonself" cells by the immune system.

How do materials arrive and leave the Golgi apparatus?

Materials arrive at the "cis" face in transport vesicles that bud off the ER, and exit the "trans" face, where they are discharged in secretory vesicles.

Describe the composition of mitochondria. And what is their role?

Mitochondria are bounded by 2 membranes: 1) A smooth outer membrane. 2) A inner folded membrane with contiguous layers called cristae. Mitochondria have their own DNA, this DNA contains several genes that produce proteins essential to the mitochondrion's role in the oxidative metabolism. Mitochondria act as a cell within a cell. Mitochondria metabolize sugar to generate ATP

What are nuclear pores? What is their role?

Nuclear pores are pores scattered over the surface of the nuclear envelope. These pores allow ions and small molecules to diffuse freely between the nucleoplasm and the cytoplasm while controlling the passage of proteins and RNA-proteins complexes.

What are the general components of the eukaryotic cell? (13)

Nucleus, Ribosomes, RER, SER, Vesicle, Golgi apparatus, Mitochondrion, Peroxisome, Plasma membrane, Lysosome, Cytoplasm, Centrioles, Cytoskeleton.

"Each ribosome is composed of 2 sub-units each of which is composed of a combination of..."? And when do these 2 join together?

Of RNA, called ribosomal RNA (rRna), and proteins. These 2 sub-units join to form a functional ribosome only when they are actively synthesizing proteins.

What are communicating / gap junctions?

Only present in multicellular organisms. They provide cytoplasmic channels from one cell to an adjacent cell. They allow communication between cells by diffusion through small openings. They allow small molecules and ions to pass from one cell to the other.

"Hydrogen peroxide is dangerous to cells because of its violent chemical reactivity" How do peroxisomes deal with this?

Peroxisomes also contain the enzyme catalase, which breaks down hydrogen peroxide into its harmless constituents, water and oxygen.

What are the 2 basic cellular architectures that we observe under microscope and what are their sizes?

Prokaryotes: 1 to 10µm in diameter. Eukaryotes: 10 to 100µm in diameter.

What are ribosomes?

Ribosomes are the cell's protein synthesis machinery.

What are septate / tight junctions? Where are they found?

Septate junctions are found in vertebrates and invertebrates and form a barrier that can seal off a sheet of cells. This form of junction between cells acts as a wall within the tissue. Tight junctions effectively segregate proteins on the opposite side of the sheet, preventing them from drifting within the membrane from one side of the sheet to the other. e.g. Tight junctions make our skin water tight, by preventing by preventing leakage between cells in our sweat glands.

What influences the direction of movement along the microtubules?

The direction is influenced by the type of motor protein involved. Kinesin: directs the movement along the microtubule toward the plus end Dynein: directs the movement in the opposite direction.

What are glycolipids? What is their relation to blood type?

They are surface proteins, composed of lipids with carbohydrate heads. They are responsible of A, B, and O blood types.

The cells of fungi, plants and many protists all have...?

Strong cell walls composed of cellulose or chitin fibers embedded in a matric of other polysaccharides and proteins.

What give cell identity in animal cells?

Surface proteins.

Since animals lack of cell walls, what plays the role of cell walls in animal cells? What is its role and composition?

The ECM (Extra Cellular Matrix) forms a protective layer composed of glycoproteins. The ECM helps coordinate the behavior of all the cells in a particular way.

What is the largest internal membrane? And what is its composition?

The ER (Endoplasmic Reticulum), composed of a phospholipid bilayer embedded with proteins.

What is the function of the Golgi apparatus?

The Golgi apparatus functions are the collection, packaging, and distribution of molecules synthesized at one location and used at another within the cell or even outside of it. Proteins and lipids manufactured in the RER and SER membranes are transported to the Golgi apparatus and modified as they pass through it. Another function of the Golgi apparatus is the synthesis of cell-wall components.

What is the RER? What is its role?

The Rough Endoplasmic Reticulum. The RER is a site of protein synthesis. The proteins synthesized on the surface of the RER are destined to be exported from the cell, sent to the lysosomes or vacuoles, or embedded in the plasma membrane.

What is the SER? What is its role? Where can we find it?

The Smooth Endoplasmic Reticulum. It is the region of the ER with relatively few bound ribosomes. An important function of the SER is to store intercellular Ca²⁺ (In muscle cells, for example, Ca²⁺ is used to trigger muscle contraction) In the liver, the enzymes of the SER carry out detoxification. Cells that carry out extensive lipid synthesis, such as those in the testes, intestine, and brain, have abundant SER.

What is the composition of the cell wall in most bacterial cells?

The cell wall is composed of peptidoglycan, which consists of a carbohydrate matrix (polymers of sugars) that is cross-linked by short polypeptide units.

What is the cytoskeleton?

The cytoskeleton is the network of protein fibers that support the shape of the cell and anchors organelles to fixed locations. This network is a dynamic system, constantly assembling and disassembling. The cytoskeleton also helps move materials within the cell.

What are plastids?

They are the collective name given to organelles like chloroplasts, leucoplasts and amyloplasts.

What is the most common alteration done by the Golgi apparatus?

The most common alteration is the addition or modification of short sugar chains, forming glycoproteins and glycolipids.

What is the role of the nucleus?

The nucleus is the repository of the genetic information that enables the synthesis of nearly all proteins of a eukaryotic cell.

What is the plasma membrane?

The plasma membrane encloses the cell and separates its contents from the surroundings. The plasma membrane is a phospholipid bilayer.

What is the nuclear envelope composed of?

The surface of the nucleus is bounded by 2 phospholipid bilayer membranes, which together make the nuclear envelope.

What is the tonoplast? Why is it called "tonoplast"?

The tonoplast is the membrane surrounding the plant vacuole. It is called "tonoplast" because it contains channels for water that are used to help the cell maintain its tonicity, or osmotic balance.

What determines the strength and shape of prokaryotic cells?

Their cell wall.

What is the composition of fungi cell walls?

Their cell walls are composed of chitin.

What is the composition of plant and protists cell walls?

Their cell walls are composed of fibers of the polysaccharide cellulose.

What are microbodies?

They are a diverse category of organelles. They are enzyme-bearing, membrane-enclosed vesicles, that are found in the cell of plants, animals, fungi and protists.

How are lysosomes activated?

They are activated by fusing with a food vesicle produced by phagocytosis.

What are grana?

They are closed compartments of stacked membranes which lie inside the inner membrane of the chloroplasts.

What is the role of Microfilaments in the cytoskeleton?

They are composed predominantly of a contractile protein called actin, which is the most abundant cellular protein, and determines the shape of cells. Microfilament's association with the protein myosin is responsible for muscle contraction. Microfilaments can also carry out cellular movements including gliding, contraction, and cytokinesis.

What is the Golgi apparatus? Give the composition of it.

They are flattened sacks of membranes. Each membrane is called cisternae.

What are flagella?

They are long threadlike structure protruding from the surface of a cell that are used in locomotion.

What are lysosomes?

They are membrane-bounded digestive vesicles. They are components of the endomembrane system.

When are lysosomes optimally active?

They are optimally active at acid ph.

What are chloroplasts? What is their role? What do they contain?

They are organelles that use light to generate AP and sugars. They can be found in eukaryotic organisms that carry out photosynthesis. They contain the photosynthetic pigment chlorophyll.

What are vesicles?

They are smaller sacs in eukaryotic cells that store and transport a variety of materials.

What is the role of lysosomes? Give an example.

They degrade proteins, nucleic acids, lipids, and carbohydrates, but also break down old organelles and recycle their component molecules to make room for new organelles. e.g. When a white blood cell, phagocytizes a passing pathogen, lysosomes fuse with the resulting "food vesicle", releasing their enzymes into the vesicle and degrading the material within.

Before cells can produce proteins in large quantity, what happens?

They first need to construct a large number of ribosomes.

What are transport proteins useful for?

They help molecules and ions move across the plasma membrane, either from the environment to the interior of the cell or vice versa.

Where do peroxisome hold their name from?

They hold their name from hydrogen peroxide, that is a by product of the activities of oxidative enzymes.

What are receptor proteins useful for?

They induce changes within the cell when they come in contact with specific molecules in the environment, such as hormones, or with molecules on the surface of the neighboring cells.

Prokaryotes lack of?

They lack of a nucleus. They have no distinct interior compartments.

Where do lysosomes made from?

They made in the Golgi apparatus.

What is the role of intermediate filaments in the cytoskeleton?

They provide tensile strength for the cell, preventing excessive stretching of cells.

What do mitochondria and chloroplasts have in common?

They share structural and functional similarities. 1) Structurally: They are both surrounded by a double membrane, and both contain their own DNA and protein synthesis machinery. 2) Functionally: They are both involved in energy metabolism.

What are the 2 types of electron microscopes?

Transmission and scanning electron microscopes.

What are vacuoles? What is their role?

Vacuoles are specialized membrane-bounded structures in plant cells. Their functions include water balance and storage of useful molecules, such as sugars, ions, and pigments. Plant cell's central vacuole is also involved in cell growth.