Exam 3 - lecture 5 Flashcards
4 phases of the first cell
Abiotic (nonliving) synthesis of simple
organic compounds
2. Abiotic polymerization of these into
macromolecules
3. Emergence of a macromolecule
capable of replication and storing
genetic information
4. Encapsulation of the first living
molecule within a simple membrane
Stanley Miller (1953
tested
the hypothesis that energy from lightning could have
powered production of simple organic compounds
from atmospheric gases.
The early atmosphere was thought to consist largely
of reduced gases such as hydrogen (H 2 ), methane
(CH4 ), ammonia (NH 3 ), and water vapor (H 2 O).
After a week of continuous exposure of gases to
electrical discharge, Miller checked the flask. He
detected two simple amino acids (alanine and
glycine).
This suggested that some organic compounds could
be produced under abiotic conditions
Deep-sea hydrothermal vents
provided ….
Deep-sea hydrothermal vents
provided a catalytic environment
for combining dissolved gases
into organic molecules.
Deoxyribonucleic acids, used to form DNA, are derived enzymatically from
the corresponding ribonucleotides
what came first RNA or DNA
bc of its strucutre and enzymatic reactions - This suggests that an “RNA world” existed before the appearance of DNA
and proteins
RNAs called ribozymes
re capable of performing certain enzymatic
reactions; for example, the formation of the peptide bonds during translation
Liposomes
Using lipids, scientists have
produced hollow, membrane-
bound vesicles
Under some circumstances,
these can carry out simple
metabolic reactions
Primordial lipids may have
come together in an early
ocean, trapping RNAs and
forming the first
“protocells”
Biologists recognized two types of cells
prokaryotes and eukaryotes
The simpler type is characteristic of bacteria (prokaryotes), and the more
complex type is characteristic of plants, animals, fungi, algae, and protozoa
(eukaryotes)
general characteristics of cells
Organizational complexity
Molecular components
Sizes and shapes
Specialization
what is the main distinction between euk and prok
The main distinction between the two cell types is the membrane-bounded
nucleus of eukaryotic cells
see slide
Based on rRNA sequence analysis, prokaryotic cells can be divided into the
widely divergent
bacteria and archaea
Sharing of a gross structural feature is ________ necessarily evidence of
relatedness
NOT
THreee domain table
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BActeria
most of the
commonly encountered single-
celled, non-nucleated organisms
traditionally called bacteri
common bacteria
Escherichia coli
Pseudomonas aeruginosa
Streptococcus lactis
archea
were originally called archaebacteria before they were discovered
to be so different from bacteria
They include many species that live in extreme habitats and have diverse
metabolic strategie
EXTREME ENVIRONMENTS no nucleus
They are considered to have descended from a common ancestor that also
gave rise to eukaryotes long after diverging from bacteria
types of archaea examples
Methanogens—obtain energy from hydrogen and convert CO 2 into
methane
Halophiles—occupy extremely salty environments
Thermacidophiles—thrive in acidic hot springs
Halophiles
occupy extremely salty environments
Methanogens
obtain energy from hydrogen and convert CO 2 into
methane
Thermacidophiles
thrive in acidic hot springs
see cell size
slide
Cell size is limited by
The requirement for adequate surface area
relative to volume
B. The rates at which molecules can diffuse
C. The need to maintain adequate local
concentrations of substances required for
necessary cellular functions
explain surface area/volume ratio size limitation
In most cases, the major limit on cell size is set by
the need to maintain an adequate surface
area/volume ratio
Surface area is important because exchanges
between the cell and its surroundings take place at
the cell surface
The cell’s volume determines the amount of
exchange that must take place across the available
surface area
( SEE SLIDE THAT FOLLOWS)
describe Cells Specialized for Absorption
Cells that are specialized
for absorption have
characteristics to maximize
their surface area
For example, cells lining
the small intestine have
microvilli, fingerlike
projections that increase
the surface area
explain diffusion rates of molecules
what is the cytoplasm?
what does it contain?
The interval volume of the cell, not including the
nucleus, is the cytoplasm
Cytoplasm contains organelles, cytoskeletal fibers,
and the semifluid cytosol in which they are
suspended
Many molecules move through this liquid-based
environment by diffusion, the unassisted
movement of a substance from a region of high
concentration to a region of low concentration
Cytoplasm contains
organelles, cytoskeletal fibers,
and the semifluid cytosol in which they are
suspended
diffusion
the unassisted
movement of a substance from a region of high
concentration to a region of low concentration
Limitation on Rates of Diffusion
The rate of diffusion of molecules decreases as the
size of the molecule increases, so the limitation is
most important for macromolecules such as
proteins and nucleic acids
Avoiding Limitations of Rates of Diffusion
Eukaryotic cells can avoid the problem of slow
diffusion rates by using carrier proteins to actively
transport materials through the cytoplasm
Some cells use cytoplasmic streaming (cyclosis in
plants) to actively move cytoplasmic contents
Other cells move molecules through the cell in
vesicles that are transported along protein fibers
Explain The Need for Adequate Concentrations of
Reactants and Catalysts
For a reaction to occur, the reactants must collide
with and bind to a particular enzyme
The frequency of such collisions is greatly
increased by higher concentrations of enzymes and
reactants
As cell size increases, the number of molecules
increases proportionately with volume
What is a solution to concentration problem
A solution to the concentration problem is the
compartmentalization of activities within specific
regions of the cell
explain Compartmentalization of Cellular Activities
A solution to the concentration problem is the
compartmentalization of activities within specific
regions of the cell
Most eukaryotic cells have a variety of organelles,
membrane-bounded compartments that are
specialized for specific functions
For example, cells in a plant leaf have most of the
materials needed for photosynthesis
compartmentalized into structures called
chloroplasts
unique properties of Eukaryotic cells that differ from archea and bacteria
A eukaryotic cell has a true, membrane-bounded nucleus
The genetic information of a bacterial or archaeal cell is folded
into a compact structure called the nucleoid and is attached to
the cell membrane
Use of Internal Membranes to Segregate Functionin bacteria and archea
Bacterial and archaeal cells do not usually contain
internal membranes
A group of photosynthetic bacteria (cyanobacteria)
have extensive internal membranes upon which
photosynthetic reactions are carried out
Some bacteria have membrane-bound or protein-
lined structures that serve as (or resemble)
organelles
describe internal membranes in eukaryotes
Nearly all eukaryotes make extensive use of
internal membranes to compartmentalize specific
functions and have numerous organelles
Examples: endoplasmic reticulum, Golgi complex,
mitochondria, chloroplasts, lysosomes,
peroxisomes, and various types of vacuoles and
vesicles
Each organelle contains the materials and
molecular machinery needed to carry out the
functions for which the structure is specialized
how do eukaryotic cells exchange materials
between compartments within the cell and the
exterior of the cell
through exocytosis and
endocytosis, processes involving membrane
fusion events unique to eukaryotic cells
chloroplasts are thought to come from
cyanobacteria
be able to label different organelles and
plant central chloroplast and vac and cell wall
do archea and bacteria have exocytosis and endocytosis
NOPE
Bacterial DNA is present in the cell
as a circular molecule, called a
chromosome, associated with few
proteins
Eukaryotic DNA is organized into
linear molecules
(chromosomes)
complexed with large amounts of
proteins called histones
Archaeal DNA is
circular and
complexed with proteins similar to
eukaryotic histone proteins
bacterial vs eukaryotic vs archaeal DNA shape
bacteria and archaeal = circular
eukaryotic = linear
bacterial DNA and Archaeal DNA
The circular DNA of bacteria or
archaea is much longer than the cell
itself and so must be folded and
packed tightly, equivalent to packing
about 60 feet of thread into a
thimble
Eukaryoitc vs prokarypotic DNA amounts
Eukaryotic cells have about 1000
times more DNA than prokaryotes
The problem of DNA packaging is
solved among eukaryotes by
organizing the DNA into
chromosomes
Prokaryotes and eukaryotes differ in how genetic
information is allocated to daughter cells upon
division —– explain
Bacterial and archaeal cells replicate their DNA and
divide by binary fission, with one molecule of the
replicated DNA and the cytoplasm going into each
daughter cell
Eukaryotic cells replicate DNA and then distribute
their chromosomes into daughter cells by mitosis
and meiosis, followed by cytokinesis, division of
the cytoplasm
Expression of DNA for eukaryotic cells
Eukaryotic cells transcribe genetic information in the
nucleus into large RNA molecules that are processed and
transported into the cytoplasm for protein synthesis
Each RNA molecule typically encodes one polypeptide
Expression of DNA in bacteria
Bacteria transcribe genetic information into RNA, and the
RNA molecules produced may contain information for
several polypeptides
In both bacteria and archaea, RNA molecules become
involved in protein synthesis
before transcription is complete
almost immediately translated into proteins - happening at the same time
A typical eukaryotic cell has what 4 components
plasma membrane, a
nucleus, membrane-bounded organelles, and the
cytosol interlaced by a cytoskeleton
In addition, plant and fungal cells have
a rigid cell
wall surrounded by an extracellular matrix
the plasma membrane surrounds
every cell
( they are like the walls of a building)
plasma membrane
It ensures that the cells contents are retained
It consists of lipids, including phospholipids and
membrane proteins, and is organized into two layers
Amphipathic Membrane Components
Each phospholipid molecule consists of two
hydrophobic “tails” and a hydrophilic “head” and
is therefore an amphipathic molecule
The lipid bilayer is formed when the hydrophilic
heads face outward and the tails face inward
Membrane proteins are also amphipathic; some, with
polysaccharides attached to them, are called
glycoproteins
Enzymes
catalyze reactions associated with the
membranes, such as cell wall synthesis
Transport proteins
move substances across the membrane
transmembrane proteins
anchor proteins aka anchors serve as
structural components of the
cytoskeleton
Receptors
for external signals trigger processes within the
cell
transmembrane proteins
The most prominent structure in the eukaryotic cell is the
nucleus
the nucleus contains
DNA and
is surrounded by the
nuclear envelope,
composed of inner and
outer membranes
The nuclear envelope
has
numerous openings
called pores, each of
which is a transport
channel lined with a
nuclear pore complex
The number of chromosomes in the nucleus is a
species-specific characteristic
Chromosomes are most easily visualized during
mitosis
whereas during interphase they are
dispersed as chromatin and difficult to visualize
Nucleoli (singular: ___________)
nucleolus
Nucleoli
are also present in
the nucleus, and are responsible for the synthesis
of rRNA
organelles involved in energy production for cells
The mitochondrion and the chloroplast are
organelles involved in energy production for cells
The mitochondrion assists with
the degradation of
sugars
The chloroplast (function)
harvests solar energy and converts
it to chemical energy in the form of ATP
what type of cells contain s mitochondria?
all eukaryotic cells
(plant cells, animals cells etc)
mitochondria = site of what type of resipiration
Mitochondria, found in all eukaryotic cells, are the site of
aerobic respiration
mitochondria size is comparable to
bacteria
structure of the mitochondria includes
inner and outer mitochondrial membrane
The inner mitochondrial membrane encloses the
matrix, a
semifluid material filling the mitochondria
describe the mitochondrial matrix
The matrix includes small circular DNA molecules that encode
some RNAs and proteins needed in the mitochondria
It also contains ribosomes involved in protein synthesis
Mitochondrial Function/ contains?
The mitochondrion contains enzymes and intermediates
needed for oxidation of sugars and generation of adenosine
triphosphate (ATP)
Many of these are found on cristae, infoldings of the
mitochondrial membrane
The chloroplast is the site of
the site of photosynthesis in plants and
algae
They are large and can be quite numerous in the cells of green
plants
Cells with high energy needs have many mitochondria,
located in
(provide two examples)
the region of the cell where the need is greatest
Such cells include sperm and muscle cells
chloroplast structure
They are surrounded by both inner and outer membranes and
contain a system of flattened membranous sacs called
thylakoids (interconnected by stroma thylakoids), stacked
into grana
chloroplast function
Chloroplasts are the site of photosynthesis, a process that uses
solar energy and CO 2 to produce sugars and other organic
compounds
Chloroplasts are found in
photosynthetic cells and contain most of
the enzymes needed for photosynthesis
Reactions that depend on solar energy take place in or on
thylakoid membrane
what type of rxn occur on thylakoid membrane?
Reactions that depend on solar energy
Reactions involved in the reduction of CO 2 to sugar occur
within the
stroma
rxn in the stroma r …
Reactions involved in the reduction of CO 2 to sugar
stroma
a semifluid in the interior of the chloroplast
Chloroplasts contain their own
ribosomes and a small, circular
DNA molecule that encodes some RNAs and proteins needed in
the chloroplast
Chloroplasts are one of several types of
plastids
Chromoplasts are
pigment-containing plastids
responsible for the coloration of flowers, fruits, and
other plant parts
Amyloplasts
specialized for the storage of
starches
The Endosymbiont Theory Proposes That
Mitochondria and Chloroplasts Were Derived
From Bacteria
Mitochondria and chloroplasts are___________ organelles
semiautonomous
organelles with many similarities to bacteria
how are mitochondria and chloroplasts similar to bacteria
Both resemble bacteria in size and shape and are
surrounded by double membranes, the inner of which
has bacterial-type lipids
All have circular DNA molecules without associated
histones
rRNA sequences, ribosome size, sensitivities to
inhibitors of RNA and protein synthesis, and type of
protein factors used in protein synthesis are all
similar
A semiautonomous organelle is
A semiautonomous organelle is a specialized subunit within a cell that has its own distinct structure and function, to some extent, operates independently of the rest of the cell, but still relies on the cell for some essential functions
The endosymbiont theory
suggests that
mitochondria and chloroplasts originated from
ancient bacteria
These gained entry into single-celled organisms
called protoeukaryotes
Protoeukaryotes may have ingested bacteria by
phagocytosis without then digesting them, allowing
a symbiotic relationship to develop
Mitochondria Apparently Evolved From
Ancient
Aerobic Bacteria
The first step toward evolution of
mitochondria
may have occurred when
an anaerobic protoeukaryote ingested
smaller aerobic bacteria by
phagocytosis
The aerobic bacteria were able to utilize
glucose of the host cell efficiently in the
presence of oxygen and could provide
the anaerobic cell with additional energy
This mutually beneficial relationship led
to the gradual loss of independence of
the bacterial cells
Chloroplasts Apparently Evolved From
Ancient
Photosynthetic Bacteria
The first step toward evolution of
chloroplasts
may have occurred when
an early eukaryotic cell (already
containing primitive mitochondria)
ingested primitive photosynthetic cells
The ingested organism probably
provided energy to the host cell in
exchange for shelter and nutrients
This mutually beneficial relationship led
to the gradual loss of functions not
needed in the photosynthetic cells’ new
environment
The Endoplasmic Reticulum
Almost every eukaryotic cell has a
network of membranes in the
cytoplasm, called the
endoplasmic reticulum (ER)
It consists of tubular membranes
and flattened sacs called
cisternae
The internal space of the ER is
called the lumen
The ER is continuous with the
other membranes in the cell
two appearances of the ER
Rough and smooth
Rough ER
Rough ER is studded with ribosomes on the cytoplasmic
side of the membrane
These ribosomes synthesize
polypeptides that accumulate
within the membrane or are
transported across it to the
lumen
Smooth ER
Smooth ER has no role in
protein synthesis
It is involved in the synthesis
of lipids and steroids such as
cholesterol and its derivatives
Smooth ER is responsible for
inactivating and detoxifying
potentially harmful
substances
Golgi Apparatus
The Golgi apparatus,
closely related to the ER in
proximity and function,
consists of a stack of
flattened vesicles known as
cisternae
It plays an important role in
processing and packaging
secretory proteins, and in
synthesis of complex
polysaccharides
It accepts transition vesicles
that bud off the ER
The Golgi Complex is Like a
processing Station
The contents of vesicles from the ER are modified
and processed in the
Golgi Complex
the golgi complex processes and modifies
contents of vesicles from the ER
The processed substances then move to other
locations in the cell through vesicles that bud off the
Golgi complex
Once processed by the Golgi
complex, materials to be exported
from the cell are packaged into
secretory vesicles
secretory vesicles release their contents through
exocytosis
These move to the plasma
membrane and fuse with it,
releasing their contents outside
the cell (exocytosisOp
The ER, Golgi, secretory vesicles,
and lysosomes make up the
Endomembrane system of the cell
what is the function of the
endomembrane system of the
cell
responsible for trafficking
substances through the cell
The Lysosome contains what enzyme and what prevents self-digestion?
Lysosomes are single-
membrane organelles that
store hydrolases, enzymes
that can digest biological
molecules
Hydrolases are sequestered
to prevent them from
digesting the contents of the
cell
A special carbohydrate
coating on the inner
lysosome membrane
protects it from digestion
Peroxisome
where are they located?
number of membranes?
size and appearance?
resemble
lysosomes in size and
appearance
They are surrounded by
a single membrane and
perform several
functions depending on
cell type
Peroxisomes are
especially prominent in
the liver and kidney cells
of animals
Hydrogen Peroixide
H 2O2 is highly toxic to cells but can be formed into
water and oxygen by the enzyme catalase
Eukaryotic cells have metabolic processes that
produce H 2O2
These reactions are confined to peroxisomes that
contain catalase, so that cells are protected from
the harmful effects of peroxide
other funcitons of peroxisomes
Peroxisomes detoxify other harmful compounds
and catabolize unusual substances
In animals, they play roles in oxidative breakdown
of fatty acids, especially longer-chain fatty acids (up
to 22 carbon atoms)
Some serious human diseases result from defects
in one or more peroxisomal enzymes, normally
involved in degrading long-chain fatty acids
peroxisomes in plants
glyosxysomes
leaf peroxisomes
During germination of fat-
storing seeds, specialized
peroxisomes called
glyoxysomes which play a role in
converting the stored fat
into carbohydrates
Leaf peroxisomes
are
prominent in photosynthetic
tissue because of their role
in photorespiration, the
light-dependent uptake of
oxygen and release of
carbon dioxide
vacuoles
Some cells contain a membrane-bounded vacuole
In animal and yeast cells, vacuoles are used for
temporary storage or transport
Phagocytosis leads to the formation of a
membrane-bounded particle called a phagosome
When this type of vacuole fuses with a lysosome,
the contents are hydrolyzed to provide nutrients to
a cell
plant vacuoles
Most mature plant cells
contain a single large vacuole
called a central vacuole
The main function of the
central vacuole is to maintain
the turgor pressure that
keeps the plant from wilting
Tissues wilt when the central
vacuole no longer presses
against the cell contents (fails
to provide adequate
pressure)
ribosomes are the site of
protein synthesis
Ribosomes Synthesize Proteins in the
cytoplasm
ribosomes are found in all cells but differ slightly in
size and composition and ribosomal RNA
Ribosome Are Numerous and Ubiquitous
Ribosomes are much more numerous than most
other cellular structures (prokaryote cells contain
thousands; eukaryote cells may contain millions)
Ribosomes in mitochondria and chloroplasts are
similar in size and composition to those of bacteria
This is particularly true of the nucleotide sequences
of their rRNAs
Ribosomes can only be seen under the
electron microscope
ribosomes are classified based on their
sedimentation coefficients
Sedimentation coefficient:
measure of how
rapidly a particle sediments in an ultracentrifuge,
expressed in Svedberg units (S)
ribosomal value for eukaryotes
80s
ribosomal value for prokaryotes
70s
Ribosomes have two subunits…
the large and small subunits
eukaryotic subunits of ribosome
80s is broken into
60s and 40s
bacteria and archaea subunits of ribosomes
70s
50s and 30s
The S values of large and small
subunits do not add up to the
value for the complete ribosome,
because
S values depend on
both size and shape
cytoskeleton
The cytoplasm of eukaryotic cells contains an
intricate, organized, three-dimensional array of
interconnected proteinaceous structures called the
cytoskeleton
The cytoskeleton function
gives a cell its distinctive shape and internal organization and plays a role in cell movement and cell division
the cytoskeleton
fix card
Proteins related to the eukaryotic cytoskeleton have
recently been discovered in bacteria and archaea
and appear to play a role in maintaining cell shape
The cytoskeleton serves as a framework for
positioning and moving organelles and
macromolecules within the cell
It may do the same for ribosomes and enzymes
Even some of the water within the cell (20–40%)
may be bound to microfilaments and microtubules
three structural elements of the cytoskeleton
Microtubules
microfilaments
intermediate filaments
Where are the ECM and cell wall located?
outside the plasma membrane
what is the extracellular structure that provides physical support to ANIMAL cells and what is it composed of?
the extracellular matrix (ECM) and consist mainly of collagen fibrils and proteoglycans
In animal cells, the ECM contains several types of junctions connecting neighboring cells
what is the extracellular structure that provides physical support to PLANT cells and what is it composed of?
For plant and fungal cells, these are cell walls, consisting mainly of cellulose microfibrils
what is the extracellular structure that provides physical support to BActerial cells and what is it composed of?
Bacterial cell walls are composed of peptidoglycans, long chains of GlcNAc and MurNAc
Processes regulated by the ECM may include
Cell motility and migration
Cell division
Cell recognition and adhesion
Cell differentiation during embryonic development
what determines ECM function and what is the primary function?
The primary function of the ECM is support, but the types of materials and the patterns in which they are deposited regulate a variety of processes
plant cell wall
The wall laid down during cell division is the primary cell wall and consists mainly of cellulose fibrils embedded in a polysaccharide matrix
It is flexible and extensible to allow for increases in cell size
Once the cell reaches its final size and shape, the rigid secondary cell wall forms by deposition of additional cellulose and lignin on the inner surface of the primary cell wall
Are plant cells motile?
Plant cells are nonmotile and thus suited to the rigidity that cell walls confer on an organism
Are animal cells motile?
Animal cells are motile and therefore are surrounded by a strong but elastic network of collagen fibers
Are Bacteria or Archaea motile?
Bacteria and archaea may be motile or not; their cell walls provide protection from bursting due to osmotic differences between the cell and the surrounding environment
cell communicationin plants
Plant cells are connected to neighboring cells by cytoplasmic bridges called plasmodesmata, which pass through the cell wall
Plasmodesmata are large enough to allow the passage of water and small solutes from cell to cell
