Cell Biology Flashcards
Cell Theory
- All living things are composed of cells
- The cell is the basic functional unit of life
- the chemical reactions of life take place inside the cell
- cells arise only from pre-existing cells
- cells carry genetic info in the form og DNA. This genetic material is passed from parent cell to daughter cell
cell components
nucleus, ribosomes, endoplasmic reticulum,Golgi aparatus, vvesicles, vaculoes, lysosomes, mitochondria, chloroplasts, centrioles.
Cell membrane
- encloses the cell and exhibits selective permeability, regulates the passage of materials in and out of the cell
- fluid mosaic model: the cell membrane consists of a phospholipid bilayer with protein embedded throughout. the lipids and many of the proteins can move freely within the membrane
- phospholipid molecules are arranged so the long nonpolar, hydrophobic, fatty chains of carbon and hydrogen face each other, with the phosphorous-containing, polar, hydrophilic heads facing outward.
- the hydrophilic heads face the watery regions inside and outside the cell, while the hyrophobic tails face each other in a water free region
- due to the lipid bilayer structure, the plasma membrane is permeable to both mall nonpolar , hydrophobic molecules (oxygen) and small polar molecules (water)
- small charged molecules cross the membrane through protein channels
- charged ions and larger charged molecules cross the membrane wuth the assistance of carrier molecules
Nucleus
controls the activities of the cell, including cell division
- is surrounded by a nuclear envelope
- contains DNA, which is complexed with structural proteins called histones to form chromosomes
- DNA winds around histones to make it more compact, and these histones are also involved in regulation of gene transcription.
- the nucleus also contains the nucleolus which is a dense structure in the nucleus where ribosomal RNA (rRNA) synthesis occurs (rRNA important for proetein synthesis at the ribosome)
Ribosome
sites of proetin production, synthesized by the nucleolus
- free ribosomes are found in the cytoplasm and prteins predentined for the ctoplasm are sythesized by free rbsomes, bound robosomes in the outer membrane of the endoplasmic reticulus and prteins destined for insertion into a membrane or secretion outside of the cell are synthesized by ribosomes bound to the rough ER
- each ribosome has a large and small subunit made of rRNA and proteins
Endoplasmic reticulum
a network of membrane-enclosed spaces involved in the transport og materials throughout the cell, especially those meant to be secreated by the cell
-2 kinds: rough and smooth
Smooth ER doesn’t have ribosomes and so isn;t involved with protein synthesis, but is involved with metabolism and the production of lipids
-Rough ER has ribosomes and plays a role in the production of proteins
prteins synthesized by the rough ER cross into the lumen of the rough ER during synthesis. Small regions of the ER bud off to form small membrane-bound vesicles that contains newly synthesized proteins, these are then transported to the golgi apparatus
Golgi apparatus
is a stack of membrane-enclosed sacs, located between the ER and the plasma membrane
- vesivles containing newly synthesized proteins bud off from the ER and fuse with the golgi
- receives vesicles and their contents from the smooth ER and then modifies and sorts them (via processes such as glycosylation), repackages them based n their destination into vesicles and distributes them to the cell surface for exocytosis
Mitochondria
sites of respiration in the cell, suppliers of energy, especially in the form of ATP,
-each mitochonrian is made of an outer and inner phopholipid layer
-outer layer has pores and selectively allows molecules to enter the mitochondria, depending on their size
space beteen inner and outer membrne called the intermembrane space
-inner membrane has many convolutins called cristae, and houses proteins f the electron transport chain
the area bound by the inner membrane is called the mitochndrial space
Cytoplasm
- where most of the cell’s metabolic processes occur
- includes the cytosol- the fluid in the cell membrane and all the organelles in the cell
- transport occurs by cyclosis (streaming movement in the cell)
Vacuoles/Vesicles
- membrane bound sacs involved in the transport and storage of materials that are ingested, secreted, or digested by the cell.
- vacuoles are larger than vesicles and are more likely to be found in plants than in animals
Centrioles
- made of microtubules and are involved in spindle organization during cell division
- not bound by a membrane
- animal cells have a pair of centrioles oriented at right angles to each other that lie in a region called the centrosome
- the centrosome organizes microtubules and helps regulate the progression of the cell cycle
- plants don’t have centrioles
Lysosomes
- membrane bound vesicles thar contain hydrolytic enzymes involved in intracellular digestion
- break down materials ingested by the cell
- maintain acidic pH of 5- lyssomal activity is greatest
- an injured or dying cell may self-distruct by rupturing the lysosomes membrane and releasing its hydrolytic enzymes- called autolysis
Cytoskeleton
-supports the cell, maintains shape, aids in cell motility, composed of microtubules, microfilaments, and intermediate filaments
-microtubules:
*hollow rods made of polymerized tubulin that radiate throughout the cell and provide it with support. Also provide a framework for organelle movement in the cell
*Centrioles-direct seperation of chromosomes during cell division, are made of microtubules,
*Cilia and flagella, specialized arrangements of microtubules that exend from certain cells and are involved in cell motility and cytoplasmic movement.
-microfilaments:
are made of two intertwined strands of actin, also important for cell movement and support, muscle contraction-based on the interaction of actin with myosin
*move materials across the plasma membrane
-intermediate filaments: made of fibrous proteins coiled into thicker cables, function in the structural support f a cell
Simple diffusion
net movement of dissolved particles down their concentration gradient- from higher concentration to region with lower concentration
-passive process, no external source of energy needed
Osmosis
- the simple diffusion of water from a region of lower solute concentration to higher concentration
- hypertonic: when the cytoplasm of a cell has a lower solute concentration than the extracellular medium, the medium is hypertonic, also called plasmolysis, causes cell to shrivel
- hypotonic: extracellular environment is less concentrated than the cytoplasm of the cell, water will flow into the cell, causing it to swell and lyse- the medium is hypotonic
- if extracellular medium is same concentration of solute as the cell cytoplasm, the cell is isotonic to the environment and water will move back and fourth in equal amounts across the cell membrane
facilitated diffusion
- a net movement of dissolved particles down their concentration gradient through special channels or carrier proteins in the cell membrane
- this process like simple diffusion (passive transport) doesn’t need energy
active transport
-net movement of dissolved particles against their concentration gradient with the help of transport proteins
-requires energy
-these carrier molecules or transport proteins aid in the regulation of the cell’s internal content of ions and large molecules
-passage of specific ions and molecules is facilitated by the following:
>symporters: move 2 or more ions or molecules in the same direction across the membrane
>antiporters: exchange one or more ions or molecules for another ion or moleule across the membrane
>pumps: energy-dependent carriers ex: sodium-potassium pump.
endocytosis
process in which the cell membrane invaginates, forming a vesicle containing extracellular medium
- allows cell to bring in large amounts of extracellular medium into the cell.
- pinocytosis is the ingestion of fluids or small particles
- phagocytosis of the engulfing of large particles
- particles may bind to receptors on the cell membrane before being engulfed.
exocytosis
- a vesicle in the cell fuses with the cell membrane and releases a large amount of contents outside the cell
- fusion of the vesicle with the cell membrane can play an important role in cell growth and intercellular signaling. ex: neurotransmitters, act as signals to neighboring cells, are released from neurons in this manner
- material never passes through the cell membrane
intracellular circulation:
- brownian movement
- cyclosis or streaming
- endoplasmic reticulum
movement of materials in a cell
- Brownian movement: kinetic energy spreads small suspended particles throughout the cytoplasm of the cell
- cyclosis/streaming: the circular movement of cytoplasm around the cell transports molecules
- endoplasmic reticulum: the ER forms a network of channels throughout the cytoplasm and provides a direct continuous passageway from the plasma membrane to the nuclear membrane
extracellular circulation:
- diffusion
- circulatory system
a number of systems deal with the movement of material on a larger scale through the body of an organism
-diffusion: if cells are in direct or close contact with the external environment, diffusion is a means of transport for food and oxygen from the environment to the cells
in larger, more complex animals, diffusion is important for the transport og materials between cells and the interstitial fluid that bathes the cells
-circulatory system: includes vessels to transport fluid and a pump to drive the circulation
Cell division
process by which a cell doubles its organelles and cytoplasm, replicates its DNA, and then divides in two
-can follow 2 different courses, mitosis or meiosis, but each is preceded by interphase
interphase
period of growth and chromosome replication
- a cell spends 90% of its life in interphase
- during this, cells perform their normal functions and each chromosome is replicated so that during division a complete copy of the genome can be distributed to both daughter cells
- after replication, the chromosome consists of two identical sister chromatids held together at a central region called the centromere
- during interphase the individual chromosomes are not visible, the DNA is instead uncoiled and called chromatin
- consists of 3 parts: G1, S, G2
- lastly M phase
stages of interphase
- G1: initiates interphase, described as the active growth phase and can vary in length. the cell increases in size and synthesizes proteins. the length of the G1 phase determines the length of the entire cell cycle
- S: period of DNA synthesis
- G2: cell prepares to divide in G2, it grows and synthesizes proteins
- M: last phase of cell cycle is the M phase. during M phase mitosis or meiosis occurs, generally resulting in either 2 identical or four non-identical daughter cells.
mitosis
- the division and distribution of the cell’s DNA to its 2 daughter cells such that each cell gets a complete copy of the original genome
- takes place in somatic cells NOT gametes
- nuclear division (karyokinesis) is followed by cell division (cytokinesis).
- stages: prophase, metaphase, anaphase, telophase, cytokinesis
Prophase
- the chromosomes condense and the centriole pairs (in animals) separate and move toward opposite poles of the cell
- the spindle apparatus forms between them and the nuclear membrane dissolves, allowing the spindle fibers to interact with the chromosome
metaphase
- centriole pairs are at opposite poles of the cell
- fibers of the spindle apparatus attach to each chromatid at its corresponding kinetochore, a protein location on the centromere
- the spindle fibers align the chromosomes at the center of the cell (equator), forming the metaphase plate
Anaphase
- the centromeres split so that each chromtid has its own distinct centromere, allowing sister chromatids to separate
- the sister chromatids are pulled toward the opposite poles of the cell by the shortening of the spindle fibers
- spindle fibers are made of microtubules
Telophase
- spindle aparatus disappears
- a nuclear membrane forms around each set of newly formed chromosomes
- thus, each nucleus contains the same number of chromosomes, diploid 2N, same as the original or parent nucleus
- the chromosomes uncoil, resuming their interphase form
Cytokinesis
- near the end of telophase, the cytoplasm divides into 2 daughter cells, each with a complete nucleus and its own set of organelles
- in animals, a cleavage furrow forms, and the cell membrane indents along the equator of the cell, eventually pinching through the cell and separating the 2 nuclei
- in plants, a cell plate forms between 2 nuclei, splitting the plant cell in half and allowing the cell to divide
Meiosis
- sexual reproduction
- differs from asexual in that 2 parents involved
- occurs via fusion of 2 gametes-parent’s sex cells
- meiosis: process by which these sex cells are produced
- similar to mitosis in that a cell duplicates its chromosomes before undergoing the process
- difference: mitosis preserves the diploid number of the cell, meiosis produces haploid (1N) cells, halving the number of chromosomes
- meiosis involves 2 divisions of primary sex cells, resulting in four haploid cells called gametes
- interphase, first meiotic division, metaphase 1, anaphase 1, nondisjunction, telophase 1, second mitotic division
Interphase
-same as mitosis, the parent’s cell’s chromosomes are replicated during interphase, resulting in 2N number of sister chromatids
first meiotic division
-produces 2 intermediate daughter cells with N chromosomes and sister chromatids
Prophase 1
- the chromatin condenses into chromosomes, the spindle aparatus forms, and the nucleoli and nuclear membrane disappear
- homologous chromosomes (chromosomes that code for the ame traits, one inherited from each parent) come together and interwine in a process called synapsis
- sometimes chromatis of homologous chromosomes break at corresponding points and exchange equivalent pieces of DNA, called crossing over
- the points of contact between homologous chromosomes when crossing over are called chiasmata,
- homologous chromosomes have crossing over, NOT sister chromatids of the same chromosome as they are identical
- the chromosomes involved in homologous recombination are left with an altered but complete set of genes
- recombination among chromosomes results in an increased genetic diversity within a species
- 2 pairs of sister chromatids are no longer identical after recombination occurs
Metaphase 1
Homologous pairs (tetrads) align at the equtorial plane and each pair attaches to a separate fiber at the kinetochore
Anaphase 1
- the homologous pairs separate and are pulled to opposite poles of the cell- called disjunction
- during disjunction, each chromosome of paternal origin separates from its homologue of maternal origin, and either chromosome can end up in either daughter cell= thus distribution of homologous chromosomes to the 2 intermediate daughter cells is random
- each daughter cell will have a unique pool of genes from a random mixture of maternal and paternal origin
nondisjunction
- occurs when cells don’t separate appropriately during meiosis
- results in cells having an incorrect number of chromosomes
Telophase 1
a nuclear membrane forms around each new nucleus
-at this point, each chromosome still consists of sister chromatids joined at the centromere
Second meiotic division
-very similar to mitosis, except meiosis 2 is not preceded by chromosomal replication
-the chromosoms align at the equator and move to opposite poles, and are surrounded by a re-formed nuclear membrane
-the new cells have the haploid number of chromosome
in women, only one of these daughter cells becomes a functional gamete, the other 2 or 3 cells are destroyed by the body
Light microscopy
light is focused in a specimen by a glass lens; the image is then magnified for projection on the eye or photographic film.
light microscopy can be used to study living cells, however the use of certain dyes or other preperations may kill live specimens
electron microscopy
a beam of electrons is used instead of light, and electromagnets are used instead of glass lenes
preparing a specimen for electron microscopy kills cells so it cannot be used to study living cells
cell fractation
cells whose cell membranes have neem ruptured are centrifuged at various speeds for varying lengths of time to seperate components of different sizes, densisties and shapes
freeze fracture
is a technique used to study cell membranes and organelles
a frozen specimen is fractures with a cold knife, producing a fracture plane that generally splits lipid bilayer membranes
methods used for studying cells and organelles
light microscopy (can study live specimens), electron microscopy (dead specimens), cell fractation (ruptured cells), freeze fracture (frozen speciemns)
Prokaryotes
single-celled organisms
complexity of cell structure in prokaryotes
simple cell structure
genetic material in prokaryotes
single circular molecule of DNA in the nucleoid region, no histones
plasmids in prokaryotes
contains plasmids which consist of only a few genes
Presence/absnce of nucleus in prokaryotes
n nucleus
RNA processing in prokaryotes
simple RNA prcessing, withut splicing
-ribosomes present
Location of transcription and translation in prokaryotes
transcription and translation occur simultaneously in cytosol
cell division in prokaryotes
cell division and asexual reproduction through binary fission
presence/Absence of cell wall in prokaryotes
most have a cell wall
presence/absence of cytoskeleton in prokaryotes
no cytoskeleton
presence/absence of centriols in prokaryotes
don’t have centrioles
presence/absece of membrane bound organelles in prokaryotes
lack membrane-bound organelles
structure of flagella in prokaryotes
flagells, but differ in structure from eukaryotes
site of respiration in prokaryotes
respiration occurs at the cell membrane
Eukayrotes
multi-cellular and non bacteria single-celled organisms
complexity of structure in Eukaryotes
complex cell structure
genetic material in Eukaryotes
genetic material= several linear strands of DNA )chromosomes) coiled around histones
plasmids in Eukaryotes
not present
presence/absence of nucleus in Eukaryotes
nucleus present
RNA processing in Eukaryotes
post-transcriptional RNA modifications; splicing, 5prime cap, poly-A tail
-ribosomes present
location of transcription and translation in Eukaryotes
transcription and translation occur seperately in nucleus and cytosol
cell division in Eukaryotes
cell division through mitosis and meiosis; sexual reproduction
presence/absence of cell wall in Eukaryotes
plants and fungi have a cell wall, animals don’t
presence/absence of cytoskeleton in Eukaryotes
cytoskeleton present
presence/absence of centrioles in Eukaryotes
have centrioles
fluid-mosaic model, plasma membrane
plasma membrane regulates passage of material s into and out of cell.
fluid mosaic model: plasma membrane has a phospholipid bilayer, phospholipids have hydrophilic and hydrophobic fatty acids
plasma membrane structure: polar phosphate group with a variable group+long hydrocarbon chain )are non-polar tails)+ fatty acid with polar and nonpolar tails
-cell can regulate fluidity of its membrane by adjusting the amount of unsaturated hydrocarbon tails present in the membrane- the unsaturated hydrocarbon tails are “bent” and thus don’t pack together as closely as saturated hydrocarbon tails.
animal cells can also regulate the fluidity of the cell membrane by adjusting the amount of cholesterol in the membrane
peroxisomes
contain oxidative enzymes that catalyze reactions in which hydrogen peroxide is produced and degraded
-break down fats into small molecules, also used in the liver to detoxify potentially harmful compounds, such as alcohol
-peroxides produced in the peroxisome could be hazardous to the cell if present in the cytoplasm, since these molecules are highly reactive and could covalently alter macrmolecules such as DNA
compartmentalization of the oxidative reactions within the peroxisomes reduces this risk
microtubules
hollow rdes made of a globular protein tubulin
involved in the movement of organelles and chromosones,
maintenance of cell shape, and cell motility
-centrioles which are found only in animal calls, are microtubule-rganizing center that anchor microtubuels during mitsos
-cilia and flagella are composed of long, stabilized microtubules arranged in a “9+2 structure”-9 pairs of microtubules surrounding 2 central microtubules for stability
cilia
are small structures that move in a whip-like fashion with the purpose of moving fluids along a cell surface or propelling a cell within a fluid
cilia line the respiratry tract to move mucus, dead cells, and other particulate matter up toward the mouth for expulsion
composed of long, stabilized microtubules arranged in a “9+2 structure”-9 pairs of microtubules surrounding 2 central microtubules for stability
flagella
composed of long, stabilized microtubules arranged in a “9+2 structure”-9 pairs of microtubules surrounding 2 central microtubules for stability
-such as those that give sperm its motility, are similar to cilia in structure but are larger
move in a wave-like fashion (cilia move in a whip like fashion)
tight junctions
cells in multicellular organisms needs a way to attach together and to communicate with one another
-this is an example of the type of junctions present in animal cells
-in tight junctions, the membranes of neighboring cells are attached, and the cells are bound together so tightly that no material can pass between cells r travel past the junction
tight junctions form a total barrier to transport and diffusion
ex: in the intestines, tight junctions form a barrier seperating the contents of the intestine from the bloodstream
anchoring junction
are found in cells subject to mechanical stress
ex: desmosomes are anchoring junctions that attach epithelial cells in the skin
gap junction
-another type of cell unction
provide a direct cnnection between the cytoplasm of one cell and the cytoplasm of a neighboring cell via channels- these channels are formed by proteins called connexins
in the heart, the flow of ions through gap junctions allows fr rhythemic, coordinated contraction of the heart muscle
