1.2 Ultrastructure of the cell

Question 1

draw, recognize and comment on this structure

Answer 1

• the nuclear membrane is double and has pores through it
• the nucleus has chromosomes wrapped around histone proteins to condense them
• uncoiled chromosomes in the nucleus are chromatids
• often densely stained chromatid areas around outside of nucleus
• nucleus is where DNA is replicated or transcribed to form mRNA which leaves via nuclear pores
• in the nucleolus ribosomes are synthesized

Question 2

draw, recognize and comment on this structure

Answer 2

the rough endoplasmic reticulum is made up of flattened membrane sacs called cisternae with ribosomes on the outside

the main function is to synesize proteins for the secretion of the cell. these proteins then pass into the cisternae and are then carried by vesciles which bud off the cisternae to the golgi

cisternae are interconnected and filled with fluid

usually found near the nucleus

Question 3

draw, recognize and comment on this structure

Answer 3

the golgi apparatus is also made up of flattened cisternae sacs but these are not as long as in the rER, are curved and do not have ribosomes on them as well as not being near the nucleus usually

the golgi apparatus processes proteins received from the rER and then usually sends them off in vesciles to be secreted by the membrane

it has enzymes to help modify the proteins

if a protein needs to be delievered within the cell a lysosome, not a vesicle, is used

Question 4

draw, recognize and comment on this structure

Answer 4

the lysosome usually looks round and it very densley stained as it is filled with high concentrations of proteins

they are formed from golgi vessles and contain digestive hydrolytic enzymes to break down ingested food in vesicles or organelles or even the whole cell

Question 5

draw, recognize and comment on this structure

Answer 5

mitochondrion are usually round or spherically, depending on which way they are sliced. are less stained than lysosomes and have crista which distinguish them

the mitochondria has a double membrane which is invaginated to form crista. The fluid inside is called the matrix and its job is to produce ATP energy in respiration

fat is digested here if it is being used as an energy source for the cell

Question 6

draw, recognize and comment on this structure

Answer 6

free ribosomes appear as dark granules on an electron microscope

they do not have a cell membrane and are about the same size as the ribosomes on the rER

they are very small and synthesize proteins and then release them to work in the cystoplasm as enzyme or similar

they are made in the nucleolus

Question 7

draw, recognize and comment on this structure

Answer 7

chloroplasts have a double membrane and are filled with stacks of thylakoids which are flattened socs of membrane. May also contain starch grains after a lot of photosynthesis

they are usually spherical or ovoid but may vary

they produce glucose etc by photosynthesis

Question 8

draw, recognize and comment on this structure

Answer 8

vesicles and vacuoles are a single membrane with fluid within them

many plant cells have vacuoles that occupy of half the cells volume

some animals absorb food from outside and digested them inside the vacuoles, some unicellular organisms use vacuoles to expell water

vesicles are small vacuoles used to transport materials inside the cell

Question 9

draw, recognize and comment on this structure

Answer 9

microtubules and centrioles are part of the cytoskeleton

roles include moving chromosomes during cell division.

centrioles are only present in animals and consist of 9 microtubules. They form an anchor point for microtubules during cell division and also for microtubules inside the cilia and flagella

Question 10

draw, recognize and comment on this structure

Answer 10

cilia and flagella are whip like projections from the cell’s surface containing a ring or 9 double microtubules and 2 central ones

flagella are larger and usually only one is present e.g. sperm

both can be used for locomotion

cillia can also be used to create a current in the fluid next to the cell

Question 11

exocrine glands of the pancreas - what do they do

Answer 11

glands secrete substances, which are released throught the plasma membrane

two types of glands in pancreas -

1. endocrine - hormones into blood
2. exocrine - digestive enzymes into small intestine

enzymes are proteins so exocrine gland cells have lots of ribosomes for making them and organelles to transport etc them

Question 12

palisade mesophyll cells

Answer 12

shape of cell roughly cylindrical

function in leaf to make glucose in photosynthesis using light energy

Question 13

the use of electron microscopes

Answer 13

electron microscopes have a much higher resolution than normal light microscopes because it is not limited by the wave length of light (400-700nm).

electron beams have a much shorter wavelength so much higher resolution about 200 times greater than in light microscopes.

eye - 0.1 mm

light microscope - 0.2 micrometer

electron microscope - 1 nm

Question 14

how do prokaryotes divide?

Answer 14

prokaryotes divide by binary fission - a form of asexual reproduction. The singular chromosome is replicated and the two copies move to opposite ends of the cell.

The cytoplasm then divides aswell. The daughter cells are genetically identical.

Question 15

describe the cell structure of prokaryotes

Answer 15

• prokaryotes have no nucleus - in contrast to eukaryotes which have a nucleus with a double membrane as a nuclear envelope
• first organisms on earth and the simplest cell structures
• all cells have cell membranes but prokaryotes also have a cell wall which protects the cell, maintains its shape and prevents it from bursting. In prokaryotes the cell wall often has peptidoglycan which is often referred to as being extra cellular
• the cytoplasm is one uninterrupted chamber filled with many biochemicals and enzymes
• prokaryotes do not have cytoplasmic organelles apart from ribosomes which are smaller than those in euaryotic cells
• the part of the cytoplasm that appears lighter on electron micrographs is usually the part that has the one circular DNA molecule- called the nucleoid

Question 16

describe the cell structure of eukaryotic cells

Answer 16

• a compartmentalized structure divided by partitions
• has organelles - like organs each organelle is specialized to perform a particular role

advantages to being compartmentalized

1. enzymes and substrates for particular processes can be much more concentrated in an area
2. organelles and their content can be moved around within the cell
3. conditions such as pH can be maintained at an ideal level for a particular process which may need to be different for different processes
4. the substances that could cause damage to a cell can be kept inside the membrane e.g digestive enzymes stored in the lysosome

Question 17

comparison of eukaryotic and prokaryotic cells

Answer 17

prokaryotic

eukaryotic

smaller - larger

always unicellular - often multicellular

no nucleus or membrane bound organelles - have both those

DNA is circular, no proteins - DNA is linear with histone-proteins to form chormatids

small ribosomes 70S - large ribosomes 80S
no cytoskeleton - always has a cytoskeleton

binary fission to divide-use meiosis or mitosis to divide

asxual reprodcution - sexual or asexual reporduction

huge variety of metabolic pathways - common metabolic pathways

rigid rotating flagellum (made of flagellin) - felxible waving cilia or flagellae (made of tubulin)

Question 18

draw a bacteria cell

Answer 18

includes

• ribosomes - smaller and less complex
• no nucleus
• no membrane bound complex organelles
• no mitochondria
• cell membrane
• cell wall - made of peptoglycan murein (chain of amino acids and carbohydrates)
• flagellum from cell wall
• i singular chromosome or strand of DNA
• plasmids
• slime capsule