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
