Monthly Archives: August 2012

2.2-3: Prokaryotic & Eukaryotic Cells

Prokaryotic Cells: the first organisms to evolve on Earth, and till today, they have remained with the most simple structure. Bacteria are small, unicellular and found everywhere, even in soil, water, pools, etc.
Cell Wall:
– always present
– made of peptidoglycan
– protects the cell
– maintains the cells shape
– prevents the cell from bursting
Ribosomes:
– small granular structures
– smaller than eukaryotic cells
– synthesizes proteins
Plasma Membrane:
– thing layer composed of phospholipids (they are pushed up against the cell way (only in healthy cells))
– partially permeable
– controls the entry & exits of substances
– pumps in or out substances
– produces ATP (through aerobic cell respiration
Cytoplasm:
– fluid filling space
– water with dissolved substances
– carries many enzymes & ribosomes
– carries out chemical reactions (metabolism)
– doesn’t contain any membrane bound organelles
Nucleiod:
– in the cytoplasm
– carries DNA (amount of DNA carried is much less than eukaryotic cells)
– stained densely than rest of cytoplasm because there are fewer ribosomes = less protein
Pili:
– protein filaments (on the external/but attached to the outside)
– can be pushed in or out by ratchet movement
– used when bacteria stick together to form a group of cells
– used when two cells are exchanging DNA (conjugation)
Flagella:
– structures also outside but attached to the cell (wall)
– they can rotate the cell to different areas (using energy)
– they are solid and flexible

Eukaryotic Cells: has a complicated internal structure (including nucleus & organelles) in the cytoplasm (single/double membranes). Each organelle has a different structure and function.
Nucleus:
– nuclear membrane is double and has pores.
– uncoiled chromosomes are spread through the nucleus: chromatin
– stores all the DNA (replicated & transcribes) (mRNA is made)
Rough Endoplasmic Reticulum:
– flattened membrane sacs = cisternae = attached are ribosomes
– purpose: synthesize protein for the cell, and then carried into the cisternae.
– then taken by vesicles (small membrane sacs) and are delivered to the Golgi body
Golgi apparatus:
– smaller cisternae (no ribosomes)
– have vesicles near by
– processes protein in vesicles (from the rER)
– then carried by vesicles to plasma membrane
Lysosomes:
– spherical with a single membrane
– formed by Golgi body vesicles
– contains high concentrations of protein (densely staining electrons)
– contains digestive enzymes = breaks down indigested good (in vesicles of breaks down organelles)
Mitochondria:
– surrounded by the double membrane
– the inner membrane is invaginated to form structures called cristae
– fluid inside is called matrix
– shape = spherical
– produces ATP for call by aerobic cell respiration
– fat is digesting here & being used for energy
Free Ribosomes:
– dark granules in cytoplasm
– not surrounded by an membrane
– synthesizes protein – releases into cytoplasm as enzymes
– ribosomes are made in the nucleolus in the nucleus

Data- Based Questions

#1.) a) i) this cell is a eukaryotic cell
ii)
iii)
b) i)
ii) if there was a 5um scale bar added to the drawing it should be 12.5mm. (2500 x 0.005)
c)

#2.) a) I – mitochondria II- nucleus III- vesicles
b) the size of the image is 50mm. Magnification = 50mm/0.0015mm = 33,333.3 x magnification
c) a scale bar of 10um would be 33.333mm on the micrograph. (33,333.3 x 0.001)
d)

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2.1c Cell Theory: Differentiation

Multicellular Organisms & Cell differentiation

– some unicellular organisms live together in colonies and each of these colonies is made up of a ball made of protein gel.

– these cells work together, but they are not fused together to form a single cell mass and one single organism.

– organisms consisting of a single mass of cells fused together are multicellular organisms

– these cells become specialized for specific functions. For example, red blood cells carry oxygen through the body.

differentiation: development of cells in different ways to perform diffferent functions.

expressed: the gene is switched ont and the information in it is used to make a protein or any other gene product.

Stem Cells

: defined as cells that have the capacity to self- renew by cell division and to differentiate.

– the human embryo consists of stem cells, but the cells eventually commit to differentiating.

– one the cell has committed to differentiateing, it may only divide six more times. But in those six times, the cells produced are different and they are not stem cells.

– very few cells remain as stem cells, and are currently active in the human body in places such as bone marrow, your skin and liver. The stem cells give your body the power to regenerate and repair cells.

– the stem cells in tissues such as the brain, kidney and heart, only allow limited repair.

– these stem cells are closely look at for it’s unique power to repair tissues, which can lead to the treating of diseases. There is a lot of potential for stem cells.

Therapeutic Use of Stem Cells

– the cells needed for the therapeutic use of stem cells, such as in bone marrow transplants, are hematopoietic stem cells (HS cells).

– HS cells divide continually to produce cells that differentiate into red and white blood cells

– just 100 HS cells and replace the blood system of mice when all the cells in the bone marrow have been destroyed by radiation

– HS can treat blood disorders such as – acute leukemia, severe combined immune deficiency, multiple myeloma and lymphoma.

Data- Based Questions

#1.) There are 11 cells in the nervous system when the larva hatched from the egg.

#2.) It took about 8 hours until the first cell division occurred. There was around 34 hours elapse before the last cell division occurred.

#3.) There was a total of 9 apoptosis occurrences during the development of the nervous system.

#4.) The maximum number of cell division to produce an adult system cell was 4 times.

#5.) The percentage of cells that are a part of the nervous system is 8.133%.

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2.1 Limitations on Cell Size

In the cells cytoplasm, a various amount of chemical reactions take place, and these reactions are known as the metabolism of the cell. The metabolic rate of the cell is proportional to the volume of the cell. The cell needs to absorb the substances needed for the reaction and remove waste, in order for the metabolism to continue. These substances move into and out of the cell through the plasma membrane.

The surface area to volume ratio is very important in a cell.

Limitations: 

– Cells do not continue growing forever, once they reach their maximum size, they divide.

– If the cell happens to grow too big, it may cause problems because it’s surface area to volume ratio becomes too small. If a cell grows, the ratio decreases.

– The rate of materials entering and leaving depends on the surface area.

– The rate at which materials are being used depends on the volume.

– Cells that generate energy may lose it if they get too big.

Units

one millimeter = 1000 x smaller than 1 meter

one micrometer (um) = 1000 x smaller than 1 micrometer

one nanometer (nm) = 1000 x smaller than 1 micrometer

1000mm=1m
1000um=1mm
1000nm=1um

Data- Based Questions

Egg Cell: The diameter of an egg cell is 100um so the radius will be 50um. The surface area of the egg cell is 3,141.60. The volume of the egg cell is 523,598.77. The surface area to volume ratio is: 0.006.

White Blood Cell: The diameter of a white blood cell is 10um so the radius is 5um. The surface area of the white blood cell is 314.15. The volume is 523.60. The ratio of surface area to volume is 0.6.

Streptococcus pneumoniae: The diameter of the streptococcus pneumoniae is 1um, so the radius will be 0.5um. The surface area of this cell is 3.14. The volume of this cell is 0.52. The surface area to volume ratio of this cell is 6.

The surface area to volume ratio decreases as the diameter of the sphere increases. The diameter of the egg cell is 100um, and it’s ratio was 0.006. The diameter of the streptococcus pneumoniae is 1um, it’s cells surface area to volume is 6.

An advantage for having a larger surface area to volume ratio is that the cell can absorb substances and nutrients with greater ease.

An egg cell is active in its metabolism, and absorbs nutrients with ease. The egg cell has only one job, and is destroyed easily. The other cells in the body need to be more efficient (smaller) to make reactions happen as fast as possible.

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2.1 Cell Theory

Microscopes were invented by Robert Hooke in the 17th century. He was the first to use the word ‘cell’, and he did this after examining cork and other plant tissues. In the next few century the cell theory developed.

Cell Theory:

– Cells are the smallest unit of life, and nothing smaller can survive independently

– All living things consist of cells, although the smallest organism may consist of only one cell

– All cells come from pre- existing cells, by division, and therefore, new cells cannot be constructed from non-living chemical substances

This wasn’t part of the reading: but I had noted it down, thinking it may be important in the near future:

Image

Unicellular Organisms

– only consists of one cell (ex. amoeba), therefore has to carry out all the ‘functions of life’

Functions of life:

Nutrition: consuming food to provide energy & growth

Metabolism: chemical reactions inside the cell (ex. cell respiration to release energy)

Growth: an irreversible increase in size

Sensitivity: understanding and responding to changes in the environment

Homeostasis: keeping conditions inside the organism to tolerable limits

Reproduction: producing offspring sexually (mitosis) or asexually (meiosis)

The structure of a single cell from a unicellular organism is more complex compared to the cell of a multicellular organism.

Extracellular Components: components that pass through the plasma membrane and form the part of the structure outside.

Magnification

: is how much larger the image is than the actual size

Formula:  magnification: size of image/actual size of specimen

Emergent Properties: those that arise from the interaction of component parts. *multicellular*

Limitations: 

– Cells do not continue growing forever, once they reach their maximum size, they divide.

– If the cell happens to grow too big, it may cause problems because it’s surface area to volume ratio becomes too small. If a cell grows, the ratio decreases.

– The rate of materials entering and leaving depends on the surface area.

– The rate at which materials are being used depends on the volume.

– Cells that generate energy may lose it if they get too big.

Units

one millimeter = 1000 x smaller than 1 meter

one micrometer (um) = 1000 x smaller than 1 micrometer

one nanometer (nm) = 1000 x smaller than 1 micrometer

1000mm=1m
1000um=1mm
1000nm=1um

Data- Based Questions

#1.) a] The size of the image (scale bar) is 20mm. The actual size of the specimen is 0.2mm, and using/plugging these figures into the formula: magnification = 20mm/0.2mm = 100 x magnification.
b] The width of this image is 26mm and the calculated magnification is 100 x. So, the magnification of 100 = 26mm/actual size = 0.26mm.

#2.) a] The actual size of this specimen in 8um which is 0.008mm. The size of the image is 62mm. The magnification = 62mm/0.008mm = 7,750 x is the magnification.
b]Now, the size of this image (scale bar) was 5um, or 0.005mm. The magnification is still 7,750 x. So the actual size of the specimen is 0.005mm x 7,750 = 38.75mm
c]The width of this image is 22mm.

#3.) a]The cheek cell has a magnification of 2000 x. If there was a 20um, 0.020mm scale bar, the actual size would be 0.020 x 2000, which equals 40mm.
b]The length of the image is 21mm.

#4.) a] The width of the chicken egg is 8mm, and the width of the ostrich egg is 24mm.
b]According to Animal Planet, a chickens egg is about 44mm wide. Magnification = 8mm/44mm = 0.18 x.

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