Cell Biology Chapter Four

Prokaryote

A unicellular organism that lacks a nucleus and membrane bound organelles

Eukaryotes

Cells that contain nuclei

Archaea

Domain of unicellular prokaryotes that have cell walls that do not contain peptidoglycan. They are also characterized by having species that live in extreme habitats on Earth and have very diverse metabolic strategies

What did Archaea derive from

Eukarya

What two categories were prokaryotes broken into

Bacteria and archaea

Why is the definition of prokaryotes not sufficient or useful?

The definition (non-nucleated cells) is a negative classification based on what cells do not have and partly because it wrongly implies a fundamental similarity among all organisms who lack a nucleus

Methanogens

A group of archaebacteria that produce methane as a by product of their metabolism.

Halophiles

"salt-loving" archaea that live in environments that have very high salt concentrations

Thermacidophiles

Hot temperature and acid loving bacteria

Average size of bacterial or archaeal cells

1-5 micrometers

Average size of animal cells

10-100 micrometers

What is the importance of the surface area/ volume ratio of a cell

The surface area of a cell effectively represents the amount of cell membrane available for the uptake and excretion defined by the cell's volume

Diffusion

the process in which there is movement of a substance from an area of high concentration of that substance to an area of lower concentration

How are cells affected by the rate of diffusion?

Cells need to be able to consistently move throughout the cell. They move based on the rate of diffusion in the cell. Diffusion is the movement of a substance from an area of high concentration of the substance to an area of low concentration

What happens to the rate of diffusion when a cell increases in size

The rate of diffusion decreases as the size of the molecule increase

What macromolecules is the rate of diffusion significant in

In proteins and nucleic acids

Cytoplasmic streaming

Another way to diffuse cellular contents throughout the cell. Moves cells through active movement and the mixing of cytoplasmic contents rather than diffusion

Why do cells need to maintain adequate concentrations within the cell

The cells contain essential enzymes and compounds that are needed for the various processes that cells must carry out. These compounds and reactants need to be able to collide with the aforementioned enzymes. The frequency of these collisions will increase proportionally with an increase in cell size. The more the cell increases along with the concentration however, there is taxing on the cell's synthetic capabilities

What feature of cells can tackle the concentration issue that occurs with an increase in cell size

Cells can compartmentalize

What is cell compartmentalization

Cells can delegate and localize concentrations necessary for cellular processes to specific compounds called organelles

Organelles

Sites of compartmentalization of cellular activities

What does compartmentalization allow cells to do

It allows cells to localize high concentration of specific enzymes and compounds needed for particular cellular processes that can then proceed efficiently

Describe Prokaryotes' lack of a nucleus

Prokaryotes lack membrane-enveloped nuclei. The genetic information of a bacterial or archaeal cell is folded in to a compact structure. This structure is attached to the cell membrane in a particular region of the cytoplasm

What is the genetic information that is folded into a compact structure in a prokaryote called

The nucleoid

Describe a Eukaryote's nucleus

The nucleus contains the bulk of the genetic information of the cell. The nucleus is surrounded by a nuclear envelope which consists of two membranes. The nucleus also has the nucleolus, chromosomes, and the nucleoplasm

Nucleolus

Synthesis site for RNA and proteins required for ribosomes

Where are chromosomes dispersed and as?

They are dispersed throughout the nucleoplasm as chromatin

Describe prokaryotes' ability to segregate function

Though there are a few bacteria that have structures that resemble organelles and have some sort of internal membranes, most conduct their cellular functions in the cytoplasm or on the plasma membrane

Cyanobacteria internal membranes

Cyanobacteria have extensive internal membranes on which photosynthetic reactions are carried out

Describe Eukaryotes' ability to segregate function

Nearly all eukaryotic cells make extensive use of internal membranes to compartmentalize specific functions and they often have numerous organelles

What are some examples of membrane surrounding and delimiting organelles

Mitochondria, chloroplasts, lysosomes, and peroxisomes as well as various kinds of vacuoles and vesicles

Structure of eukaryotic nucleus

Cytoskeleton

a microscopic network of actin filaments and microtubules in the cytoplasm of many living cells that gives the cell shape and coherence/elasticity

Parts of the cytoskeleton

microtubules, microfilaments, and intermediate filaments

Microtubules basic function

found in the cilia and flagella of many cell types. They are the largest elements of the cytoskeleton. They play a role in motility and chromosome movement as well as the organization of the cytoplasm and intracellular movement of macromolecules and other materials in the cell. They also contribute to the overall shape of the cell, the spatial disposition of its organelles, and the distribution of microfilaments and intermediate filaments

Microfilaments

Found in the muscle fibrils and other structures involved in motility. They are best known for their roles in contraction and motility. The specific thing they are best known for is their role in the contractile fibrils of muscle cells. They can also form connections with the plasma membrane and thereby influence locomotion, amoeboid movement, and cytoplasmic streaming. They also produce the cleavage furrow that divides the cytoplasm of an animal cell after the two sets of chromosomes have been separated by mitotic spindle fibers. They also contribute importantly to the development and maintenance of cell shape

Intermediate filaments function

Especially prominent in cells that are subject to stress. They are seen as a scaffold that supports the entire cytoskeletal framework. They are also thought to have a tension-bearing role in some cells because they often occur in areas that are subject to mechanical stress,

What kind of cells are cytoskeletons found in

eukaryotes

Endocytosis

One of the processes of membrane fusion is found in eukaryotes. Portions of the plasma membrane invaginate and are pinched off to form membrane-bounded cytoplasmic vesicles containing substances that were previously on the outside of the cell

Exocytosis

One of the processes of membrane fusion found in eukaryotes. Membrane-bounded vesicles inside the cell fuse with the plasma membrane and release their contents to the outside of the cell

The organization of DNA for prokaryotic cells

Prokaryotic cells have circular DNA that is associated with a few amount of proteins. Though very long (much longer than the bacteria or archaea cells themselves) the DNA is folded compactly in the cell.

The length of bacterial and archaeal cells in comparison to their DNA

Bacteria and archaea are typically only about a micrometer long while their DNA can be as long (or longer) that 1300 micrometers in circumference (it is circular)

The organization of DNA for eukaryotic cells

Some eukaryotic cells (like yeast or fruit flies) have about 10 to 50 times the amount of DNA that bacterial and archaeal cells possess, but many can have as much as 1000 times as much DNA! Size is not an issue with DNA in eukaryotic cells however given that they can organize their DNA into complex structures called chromosomes which contain as many histone proteins as DNA

How do Bacterial cells segregate their genetic information

They do so using the simple process of binary fission which results in bacteria dividing and giving one molecule of the replicated DNA and half of the cytoplasm going to each daughter cell

How do eukaryotic cells segregate genetic information

They do so through the processes of mitosis and meiosis. Chromosomes are distributed equally to the daughter cells. Cytokinesis follows the processes of mitosis and meiosis.

How do eukaryotic cells express DNA

They tend to transcribe genetic information in the nucleus into large RNA molecules and depend on later processing and transport processes to deliver RNA molecules of the proper sizes to the cytoplasm for protein synthesis. Each RNA molecule typically encodes one polypeptide

How do prokaryotic cells express DNA

Bacteria transcribe very specific segments of genetic information into RNA messages and often a single RNA molecule contains the information to produce several polypeptides. In bacteria, little to no processing of RNA occurs; a moderate amount is seen in archaea though less than in eukaryotes

Unity in cells

All cells resemble each other in fundamental ways.

Unity in cells: Function

Virtually all cells oxidize sugar molecules for energy, transport ions across membranes, transcribe DNA into RNA and undergo division to generate daughter cells

Unity in cells: Structures

all cells are surrounded by a selectively permeable plasma membrane, all have ribosomes for the purpose of protein synthesis, and all contain double-stranded DNA as their genetic information

Why do we also study diversity of cells

it is important to study the features that are especially prominent in a particular cell type to understand how certain processes work

What cell would be good to study to understand how the process of protein secretion works

it is advantageous to consider a cell that is highly specialized for that particular function. Cells from the human pancreas are a good choice for studying this process because they secrete large amounts of digestive enzymes.

The division of labor in specialized structures in eukaryotes vs prokaryotes

Single celled organisms must be able to carry out any and all of the functions necessary for survival, growth, and reproduction. It typically does not overemphasize any single function at the expense of others. Eukaryotes, however, are characterized by their division of labor that they have among tissues and organs that not only allows for but also depends on specialization of structure and function. Whole groups of cells become highly specialized for a particular task, which then becomes their specific role in the overall functioning of the organism.

What four major structural features does a typical eukaryotic cell possess

An external plasma (or cell) membrane to define its boundary and retain its contents, a nucleus to house the DNA that directs cellular activities, membrane-bounded organelles in which various cellular functions are localized, and the cytosol interlaced by a cytoskeleton of microtubules and microfilaments

What do eukaryotic plant cells possess

In edition to the four main structural elements all eukaryotic cells possess, plant and fungal cells have rigids cells walls external to the plasma membrane while animal cells do not

Instead of a cell wall, what are animal cells surrounded by

an extracellular matrix consisting primarily of proteins that provide structural support

Plasma Membrane

It surrounds every cell. It defines the boundaries of the cell and ensures that its contents are retained.

What does the plasma membrane consists of

Phospholipids, other lipids, and proteins and is organized into two layers

What does each layer of the plasma membrane contain

Two hydrophobic "tails" and a hydrophilic "head" which makes the structure amphipathic

Lipid bilayer

general structural of all plasma membranes which in turn is the basic structural unit of virtually all membranes and serves as a permeability barrier to most water-soluble substances

What are the membrane proteins in terms of affinity to water

They are amphipathic

Glycoproteins

protein with hydrophilic regions exposed on the external side of the plasma membrane and short carbohydrate side chains known as oligosaccharides attached to them

The different types of membrane proteins

enzymes, anchors, transport proteins, receptors, and transmembrane proteins

Membrane enzymes

catalyze reactions known to be associated with the membrane such as cell wall synthesis

Membrane anchor proteins

Structural elements of the cytoskeletons

Membrane transport proteins

Responsible for moving specific substances (ions and hydrophilic solutes) across the membrane

Membrane receptor proteins

receive external signals that trigger specific processes within the cell. They bind to specific molecules

Transmembrane proteins

they have hydrophilic regions protruding from both sides of the membrane. These regions are connected by one of the more hydrophobic, membrane-spanning domains

Types of transmembrane proteins

transport and receptor proteins

What does the nucleus of eukaryotic cells serve as

The information center of the cell

Nuclear envelope

Made up of the inner and outer nuclear membranes

What is unique to the membranes of the nuclear envelope

small opening called pores

What do nuclear pores do

Each pore is a channel through which water-soluble molecules and supramolecular complexes can move between the nucleus and cytoplasm. Ribosomal subunits, messenger RNA molecules, chromosomal proteins, and enzymes needed for nuclear activities are transported across the nuclear envelope through its pores.

Chromatin

chromosomes during interphase. They are DNA-protein fibers

nucleoli

synthesizes the RNA and protein components needed to form the ribosomes

What is the cytoplasm referred to as?

The internal volume of the cell exclusive of the nucleus

What is mitochondria the site of

aerobic respiration

What are the dimensions of an average mitochondria

1 micrometer across and several micrometers long

Mitochondrial features

Mitochondria have two inner and outer cell membranes They also have small, circular molecules of DNA that encode some of the RNAs and proteins needed along with the ribosomes involved in protein synthesis

What is mitochondria's main function

To oxidize sugars and other cellular "fuel" molecules to carbon dioxide in the effort to extract energy from food molecules to be conserved as ATP (adenosine triphosphate)

What important cellular processes occur in the mitochondria

The TCA cycle, fat oxidation, and ATP generation

Cristae

Infoldings of the inner mitochondrial membrane

What is found in the cristae

Molecules that are involved in transporting electrons from oxadizable food molecules to oxygen

Mitochondrial matrix

semi-fluid matrix that fills up the inside of the mitochondrion

What occurs in the mitochondrial matrix

the other reaction sequences, particularly those of the TCA cycle and those involved in fat oxidation

How are mitochondrion localized

They are located where the energy need is greatest

MtDNA

the genome of the mitochondria

How many base-pairs long are MtDNA

it is 16,500 base-pairs long

How many genes does mtDNA code for

37

Chloroplasts

the site of photosynthesis in plant cells

Dimensions of chloroplasts

A few micrometers in diameter and about 5-10 micrometers long making them larger than mitochondria (but not, mostly, larger than nucleus)

Structure of chloroplasts

Have three membranes; an inner and outer membrane and a membrane built of thylakoids that are interconnected by stroma thylakoids

Grana

Thylakoids stacked together

What is the mitochondria capable of encoding

some but not all of its own proteins

What can human mitochondrial DNA genes encode

22 of them specify transfer RNAs (tRNAs), 2 specify ribosomal RNAs (rRNAs) and the remaining 13 encode polypeptides all of which are components of the respiratory complexes that carry out oxygen-dependent ATP synthesis

What are located in chloroplasts

the enzymes, intermediates, and light-absorbing pigments needed for photosynthesis

Photosynthesis

the enzymatic reduction of carbon dioxide to sugar

What reactions occur in the thylakoid membrane system

reactions that depend directly on solar energy

What reactions occur within the stroma

Reactions involved in the reduction of carbon dioxide to sugar molecules

Stroma

the semi fluid material that fills the interior of the cholorplast