Lecture 3: Prokaryotes and eukaryotes Flashcards
What does “karyote” mean from Greek?
nucleus
What does prokaryote mean?
“before nucleus”
no nucleus
What does eukaryote mean?
“well (proper) nucleus”
with nucleus
What do prokaryotes include?
Eubacteria (Greek - “true” bacteria) - live in many habitats
Archaebacteria (Greek - “ancient” bacteria) - called archae; live in habitats similar to bacteria, but can also in extreme environments
Thermophiles
Acidophiles
Halophiles
Piezophiles
extreme heat
low pH or acidic
high salt (NaCl)
high pressure environments
What can bacteria do?
form into chains or clusters
use various food sources
convert energy of the sun into food through photosynthesis
Which (only) bacteria have extensive internal membranes (for photosynthesis)?
a group of photosynthetic bacteria (cyanobacteria)
What is the function of flagella in bacteria?
helps bacteria move in water
What is the function of fimbriae/pili in bacteria?
=small bristle-like fibers that allow bacteria to attach to surfaces
What are sex pili used for?
to transfer DNA from one bacteria to another
What gives bacteria protection against changes in osmotic pressure?
the bacteria cell wall
What are bacteria cell walls composed of?
peptidoglycolans: long chains of modified sugars N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc)
peptido - short peptides, protein chains
glycans - crosslinked with sugars
they held together by peptide bonds between a small number if amino acids, forming a netlike structure
the envelop of gram-negative bacteria
2 membranes - cell and outer membrane
peptidogltycan layer - only 1-2 layers thick
the envelop of gram-positive bacteria
only one membrane
peptidoglycan layer can be 40 layers thick
What is Gram stain?
cells are stained with “crystal violet” dye and then washed
gram stain causes gram-positive -> purple; gram-negitive -> pink
What is used as a counterstain?
safranine
some bacteria contain Glycocalyx
What is it?
Glycoprotein-polisaccharide covering that surrounds the cell membrane
it can form a tight capsule/loosely attached slime
it’s common in soil bacteria
no cell wall, no glycocalix in?
mycoplasma (eubacteria)
thermoplasma (archae)
Bacterial DNA is usually a single circular dsDNA. Where is it located?
in an irregularly shaped nucleoid, which is not surrounded by membrane
5 steps of prokaryote multiplication by binary fission
- cell replicates its DNA (in nucleoid)
- The cytoplasmic membranes elongates, separates DNAs
- Cross wall forms; membrane invaginates
- Cross forms completely
- Daughter cells are formed
What do eukaryotes possess as their genetic material?
double-stranded linear DNA
What does a typical eucaryotic cell have?
plasma membrane
organellas
cytosol
cytoskeleton
What do plant and fungal cells have in addition?
a rigid cell wall surrounded by an extracellular matrix
Describe the phospholipid bilayer of plasma membrane
plasma membrane: phospholipids, other lipids, and membrane proteins -> two layers
each phospholipid molecule consists of two hydrophobic “tails” (face inward) and a hydrophilic “head” (face outtward) and is therefore an amphipathic molecule
What are 5 functions of membrane proteins?
- channel
- transport
- receptor
- enzymatic
- junction
channel proteins
simple protein pores that allow substances to move across the membrane
transport proteins
bind to substances to assist their movement across membranes
receptor proteins
have a shape that can only bind to specific signal molecules
enzymatic proteins
membrane proteins that carry out chemical reactions
junction proteins
connect cells to each other and allow them to communicate
Some organellas are surrounded by a membrane. What do membrane-bound organellas include?
nucleus
mitochondria/chloroplasts
golgi apparatus
endoplasmic reticulum
lysosomes/peroxisomes
Which organellas have endosymbiotic (A symbiotic relationship where one organism lives inside the other) origins?
mitochondria and chloroplast
surrounded by 2 membranes (double - membrane organelle) and contains the cell’s genomic DNA in the linear form
nucleus
2 membranes (outer, inner) = nuclear envelope
in nuclear membrane
permits the passage of ribosomal subunits and RNA, proteins out of -> into the nucleus
nuclear pores (=multiprotein complex)
What is produced in the nucleus?
RNA, a nucleic acid
What is the function of mRNA?
acts as an intermediary to DNA and carries the information for the amino acid sequence of a protein
What is the function of rRNA?
combines with the specific proteins to form the subunits of ribosomes
What is the function of nucleolus?
site of rRNA synthesis
Where can ribosomes be found in eukaryotic cells?
in the cytoplasm (free)
attached to the endoplasmic reticulum (ER) (membrane-bound)
Which organelle is continuous with the membrane of the nucleus?
endoplasmic reticulum
2 subpopulations of ER based on appearance and function
rough - has ribosomes - synthesizes proteins - these proteins are packaged in transport vesicles
smooth - synthesize lipids (cholesterol, steroid hormones) - plays role in carbohydrate metabolism and detoxification (of harmful things)
What is the function of ER?
site of the initial production of materials for use inside and outside of the cell
it’s single membrane
appears as an irregular maze of interconnected spaces
Most cells have very little smooth ER. What is the exception?
Hepatocytes
What is the function of Golgi Apparatus?
receives molecules from rough ER and chemically modifies and processes them before release from the cell
What is Golgi apparatus composed of?
a series of flattened sacs (vesicles - cisternae)
What is the function of lysosomes?
digest molecules/structures within the cell
What is the function of peroxisome?-
animal peroxisomes: uses oxidative reactions to break down molecules (fatty acids-lipids), detoxify compounds (alcohol, phenols)
involved in the biosynthesis of some phospholipids
plant: glyoxysomes - converting stored fat into carbohydrates
generating and degrading hydrogen peroxide (H2O2)
What is a byproduct of oxidative reactions of peroxisome?
Why they must be neutralized?
How neutralized?
Hydrogen peroxide H2O2
corrosive and toxic to cells
peroxisomes contain an enzyme (catalase) that breaks down H2O2 to H2O and O2
The ER, Golgi, secretory vesicles, lysosomes form ____ system
What is its function?
Endomembrane system
responsible for trafficking substances through the cell
What provides energy for the cell?
Mitochondria - contains enzymes and intermediates for degradation of sugars + generation of ATP (aeorobic respiration)
Chloroplasts - harvests solar energy - converts to chemical energy in the form of ATP
Mitochondrial structure
inner and outer mitochondrial membrane
inner: matrix, semifluid material (fills it)
matrix: small circular DNA molecules (encode some RNAs and proteins needed in mitochondria) and ribosomes (involved in protein synthesis)
Structure of chloroplast
Grana - thylakoids (flattened membranous sacs) - connected by stroma thylakoids
photosynthesis happens in/on thylakoid membranes
stroma: reduction of CO2 to sugar
What is the function of cytoskeleton?
gives a cell distinctive shape and internal organization
plays a role in cell movement and division
serves as framework for positioning and moving organellas, macromolecules within the cell
organelle made of protein tubulin proteins (alpha and betta) arranged to form hollow cylinders
microtubules
(assembled by the centrosome in animal cell)
can be associated with motor molecules (kinesin and dynein)
What is the structure and function of actin filaments?
2 chains of globular actin monomers interwined in a helix
support the cell and any projections (microvill)
cell movemement
(with myosin) -> muscle contraction and cell division
What is chromatin
a mixture of DNA and proteins that form the chromosomes
vacuole
In animal and yeast cells: temporary storage or transport
Plant cells: central vacuole - maintaining the turgor pressure that keeps plant tissue from wilting
The three major structural elements of the eukaryotic cytoskeleton
microtubules, composed of tubulin subunits,
microfilaments, composed of actin subunits,
intermediate filaments
extracellular matrix (ECM) For many animal cells consist of
function
collagen fibrils and proteoglycans
cell motility and migration, cell division, cell recognition and adhesion, and cell differentiation during embryonic development
cell wall for plant and fungal cells consist of
cellulose microfibrils
Primary walls are quite flexible and ex-tensible, which allows them to expand somewhat in response to cell enlargement and elongation. As a cell reaches its final size and shape, a much thicker and more rigid secondary cell wall may form ( defines the final size and shape of the cell)
