Cell Biology Flashcards
mitochondria
“power house of cell”- energy released
A double membrane surrounds mitochondria and inside fluid is called matrix. They produce ATP for the cell by aerobic cell respiration. Fat is digested here if it is being used as an energy source in the cell.
free ribosome
They synthesise protein, releasing it to work in the cytoplasm, as enzymes or in other ways. Ribosomes are constructed in a region of the nucleus called the nucleolus. Not surrounded by a membrane and known as 80S.
nucleolus
functions in protein synthesis
nucleus
control center of cell (controls all activities)
cell wall
(only plant, unicellular, bacteria) outer boundary, for protection, maintains the shape of the cell
cell (plasma) membrane
outer boundary, regulates the movement of substances into and out of the cell (semi-permeable)
lysosomes
Formed from Golgi vesicles and contain high concentrations of protein, which makes them densely staining in electron micrographs. They contain digestive enzymes, which can be used to break down ingested food in vesicles or break down organelles in the cell or even the whole cell (self-destruction). They are also used by phagocytes to digest ingested particles.
vacuoles and vesicles
Single membrane with fluid inside. Many plants cells have large vacuoles storing various substances, some animals absorb foods from outside and digest them inside vacuoles. Some unicellular organisms use vacuoles to expel the more-than-needed-water.
Vesicles are very small vacuoles used to transport materials inside the cell.
cytoplasm
gel like substance (main ingredient is water), site of most chemical reactions in the cell
chromosomes
function in hereditary, collection of genes
genes
individual units or hereditary
chloroplasts
(only in plants) Double membrane surrounds the chloroplast, which contains chlorophyll which contains stacks of thylakoid. They produce glucose and a wide variety of other organic compounds by photosynthesis.
Golgi bodies
package and transports certain substances
centriole/ cetrosome
(only in animals), function in cell division
nuclear membrane
outer boundary of the nucleus, protects it by regulating the movement of substances into and out of the nucleus through the nuclear pore.
Levels of Organisation
cells = the smallest structural and functional unit of an organism
tissues = a group of similar cells preforming a particular task (blood, xylem, phloem, etc.)
organs = a structure composed of different tissues fulfilling a function (heart, leaves of plants, etc.)
organ system = a combination of organs working together (the circulatory system)
extra cellular matrix
The cell membrane around a single cell organism has an additional outer layer called extra cellular matrix, which gives stability, protection, maintains the shape and prevents from bursting and anchor the cilia sometimes.
pilli
Protein rods projecting from the cell wall and extracellular matrix. Helps cell to “stick” to other surfaces.
nucleoid
(in prokaryotes) Region of cytoplasm which contains naked DNA
Rough endoplasmic reticulum (rER)
The rER consists of flattened membrane sacs, called cisternae. Attached to the outside of these cistern are ribosomes. They are larger than in prokaryotes and are classified as 80S. The main function of the rER is to synthesize protein for secretion from the cell. Protein synthesized by the ribosomes attached to the rER and are passed into its cisternae and is then carried by vesicles, which bud off and are moved to the Golgi apparatus. — series of canals used for intracellular transport
Golgi apparatus
This organelle consists of flattened membrane sacs called cisternae, like rER. However the cisternae are not as long, are often curved, do not have attached ribosomes but many vesicles nearby. The Golgi apparatus processes proteins brought in vesicles from the rER. Most of these proteins are then carried in vesicles to the plasma membrane for secretion.
Cilia and flagella
used for locomotion/movement:
•Flagella is a protein structure projecting from cell wall, with corkscrew shape, rotate to cause locomotion.
•Cilia beats rhythmically and help push things around like in the fallopian tube connected to the uterus or in our airways
organelles with a double membrane
- nucleus
- mitochondrion
- chloroplast
organelles with a single membrane
- ER (rough and smooth)
- Golgi apparatus
- vesicles: lysosome, secretory vesicle, pinocytic vesicle, phagocytic vesicle, food vacuoles
organelles with no membrane
- microtubules and microfilaments
* ribosomes (poly-ribosomes)
three differences between plant and animal cells
Plants cell do have following but animals not:
- cellulose cell wall
- mature cell containing large vacuole
- may contain chloroplast
biological membranes consist of…
- phospholipids
- cholesterol (reduces membrane fluidity and permeability to some solutes)
- proteins (integral and peripheral)
- glycoproteins and glycolipids
image size, actual size, magnification
Magnification = image size / actual size
Cell Theory (four commonalities and exceptions) \+ general cell facts
- Cells are the basic units of structure and function of all living things
- All cells arise from pre-existing cells (except the first cell?)
- smallest organism = unicellular (one cell, nothing smaller can survive) —> Larger=multicellular (many cells with specialization)
- emergent properties
- surrounded by a membrane
- genetic material
- chemical reactions, catalysed by enzymes
- own energy release system
Exceptions:
- Viruses: a package of genetic material (DNA or RNA) enclosed in a protein envelope.
- Slime molds
Limitations of cell size
metabolism needs absorption and excretion of substances
surface area to volume ratio:
- If the ratio is too small then substances will not enter the cell as quickly as they are required and waste products will accumulate because they are produced more rapidly than they can be excreted.
- If the ratio of surface area to volume is too small, then the cell may overheat because the metabolism produces heat (energy) faster than it is lost over the cell’s surface.
The two key properties of stem cells
- Stem cells can divide again and again to produce copious quantities of new cells. They are therefore useful for the growth of tissues or the replacement of cells that have been lost or damaged.
- Stem cells are not fully differentiated. They can differentiate in different ways, to produce different cell types. (omni potent)
Gradually during embryo development the cells commit themselves to a pattern of differentiation. (Eventually each cell becomes committed to develop into one specific cell type. By becoming specialised, the cells in a tissue can carry out their role more efficiently than if they have many different roles. They can develop the ideal structure to carry out their function.
Some cells remain as stem cells and are still present in the adult body. They are present in human tissues such as bone marrow, skin and liver, which gives those tissues considerable powers of regeneration and repair.
order the sizes of bacteria, most cells, viruses, molecules, membrane thickness, organelles
molecule (1nm) membrane thickness viruses bacteria organelles most cells (up to 100µm)
cell devision in prokaryotes
binary fission - asexual reproduction
The single circular chromosome is replicated and the two copies move to opposite ends of the cell. Division of the cytoplasm quickly follows. Each of the daughter cell now contains one copy of the chromosome, making them genetically identical.
Comparing prokaryotic and eukaryotic cells
naked DNA / DNA wrapped around histones
DNA in nucleoid / DNA in nucleus
mitochondria not present / present
ribosomes are small 70S / ribosomes are large 80S
no or few internal membranes / many compartmentalizations
plasma membrane:
hydrophobic or hydrophilic? : phosphate heads, hydrogen carbon tails
phosphate heads are hydrophilic
hydrocarbon tails are hydrophobic
intergral and peripheral membrane proteins (description and function)
Functions of membrane proteins:
Hormone binding site, enzymes, electron carriers, channels for passive transport, pumps for active transport
Integral proteins
are hydrophobic on at least part of their surface and they are therefore embedded in the hydrocarbon chain in the centre of the membrane. Many integral proteins are transmembrane — they extend across the membrane, with hydrophilic parts projecting through the regions of phosphate heads on either side.
Peripheral proteins
are hydrophilic on their surface, so are not embedded in the membrane. Most of them are attached to the surface of integral proteins and this attachment is often reversible. Some have a single hydrocarbon chain attached to them which is inserted into the membrane, anchoring the protein to the membrane surface.
phospholipids bilayer
Phospholipids
allow for membrane fluidity; important in cytosis
Hydrophilic heads
made from glycerol and phosphate; stabilized by surrounding water and other heads
Hydrophobic tails
made from two fatty acids; held together by hydrophobic interactions
Endo- and exocytosis (+ one example each)
Endocytosis - vesicles absorbing substances into the cell
Proteins carry out the process of endocytosis using energy from ATP.
example: undigested food
Exocytosis - releasing substances using vesicles
example: digestive enzymes from the gland cells
In a growing cell, the plasma membranes grows through exocytosis.
In detail: Phospholipids are synthesised next to the rER and become inserted into the rER membrane. Ribosomes on the rER synthesise membrane proteins which also become inserted into the membrane. Vesicles buds off the rER and move to the plasma membrane and fuse with it.
types of membrane transport and details
passive transports (no energy) - higher to lower concentration (result of random motion) • simple diffusion - semi-permeable membranes allow hydrophobic *uncharged* particles to diffuse • facilitated diffusion - channel proteins allow *charged* particles (uniport = one particle, symport = more than one particle, anitport = both directions different particles) • osmosis - low to high solute concentration
- active transport - protein pumps, against concentration gradient (low to high), ATP, specificity
- cytosis - vesicles
Pasteur’s experiment
- swan neck glass blocked organisms to get in; no spontaneous generation of cells occur; cells must come from pre-existing cells
- there had to be a first cell
endosymbiotic theory (description + evidence)
explains the origin of eukaryotic cells:
- Mitochondria were once free-living prokaryotic organisms that had developed the process of aerobic cell respiration. Larger prokaryotes that could only respire anaerobically took them in by endocytosis. Instead of killing and digesting the smaller prokaryotes the allowed them to continue to live in their cytoplasm - mutualistic relationship. Natural selection favored them.
- Same with chloroplast.
evidence:
- 70S ribosomes in mitochondria and chloroplasts
- naked DNA in both
- both divide by binary fission
- there is a second membrane on both
- the genetic code in both is slightly different, suggesting later divergence and mergence
Mitosis
The division of the nucleus into two genetically identical daughter nuclei (embryonic development, roots, tissue repair, asexual reproduction).
process happening in interphase
- protein synthesis
- DNA replication (the copying of DNA)
- an increase in the number of mitochondria and/or chloroplasts (these organelles divide like bacteria).
- Cells which do not divide, don’t continue after the S-Phase (DNS Replication) and enter the G0 phase, which may be temporary or permanent.
phases of the cell cycle
interphase consisting of:
G1 (cellular contents, excluding chromosomes, are duplicated)
S (each of the 46 chromosomes is duplicated)
G2 (double checks duplications and repairs)
- mitosis*
- cytokinesis* (cleavage furrow or cell plate)
phases of mitosis
- Prophase*
- supercoiling
- nucleolus breaks down
- microtubules grow from structures called microtubule -organising centres (MTOC) to form spindle-shaped array -that links the poles of the cell. MTOC = centrioles
- at the end, the nuclear membrane breaks down.
- Metaphase*
- Microtubules continue to grow and attach to the centromeres on each chromosome. The two attachment points on opposite sides of each chromosome allow the chromatids of a chromosome to attach to microtubules from different poles.
- Microtubules are all put under tension to test whether the attachment is correct. This happens by shortening of the microtubules at the centromere.
- If the attachment is correct, the chromosomes remain on the equator of the cell.
- Anaphase*
- Centromere divide, allowing the pairs of sister chromatids to separate.
- The spindle microtubules pull them rapidly towards the poles of the cell.
- Mitosis produces two genetically identical nuclei because sister chromatids are pulled to opposite poles.
- Telophase*
- Chromatids have reached the poles of the cell.
- Nuclear membrane reforms around them.
- Chromosomes uncoil and a nucleolus is formed.
- By this stage of mitosis the cell is usually already dividing and the two daughter cells enter interphase again…
cytokinesis
in animal cells: cleavage furrow forms as the plasma membrane is pulled away from equator.
in plant cells: because cell walls no cleavage furrow, instead a cell plate forms across the old metaphase plate Done by vesicles fusing together at the plate.
cyclins
A group of proteins used to ensure that tasks are performed at the correct time during the cell cycle and that the cell only moves on to the next stage of the cycle when it is appropriate.
Cyclins bind to enzymes called cyclin-dependent kinases. These kinases then become active and attach phosphate groups to other proteins in the cell. The attachment of phosphate triggers the other proteins to become active and carry out tasks specific to one of the phases of the cell cycle.
There are four main types of cyclin in human cells. Unless these cyclins reach a threshold concentration, the cell does not progress to the next stage of the cell cycle.
types of tumours (mutagens, oncogenes, metastasis)
- Tumours (cancers) are the result of uncontrolled cell division and can occur in any organ or tissue at any stage of life.
- In benign cancers, cells adhere to each other and do not invade nearby tissues or move to other parts of the body.
- In malignant cancers, the cells can become detached and move elsewhere in the body and develop into secondary tumours.
- Mutagens* = an agent that causes genetic mutation, such as radiation or a chemical substance. Mutations may cause cancer: they are random changes to the base sequence of genes. (Most genes do not cause cancer if they mutate)
- Oncogenes* = mutated genes causing cancer. In a normal cell, oncogenes are involved in the control of the cell cycle and cell division. That’s why mutations in them can result in uncontrolled cell division and therefore tumour formation.
- Metastasis* = the movement of cells from a primary tumour to a secondary tumour.
hypertonic, hypotonic, isotonic
hypertonic = more concentration hypotonic = less concentration isotonic = same concentration
