1.2 Ultrastructure Of Cells

Question 1

Scanning vs transmission electron microscope

Answer 1

Scanning (SEM) - electrons focused on the surface of a specimen to provide an image that appears 3D

Transmission (TEM) - electrons focused thru a sample, used to study internal structure of cells

Question 2

three domains of biological classification

Answer 2

1. archaea – “primitive”, mainly microorganisms
2. bacteria
3. eukaryota
   organisms under both archaea and bacteria are prokaryotes

Question 3

describe the cell structure of prokaryotes

Answer 3

• genetic mat NOT encased in membrane, coiled into nucleoid
• do not contain membrane-bound organelles
• cytoplasm within plasma membrane
• one chromosome – circular DNA
• may cont plasmids, extra-chromosomal dna

Question 4

how do mesosomes form in prokayotes

Answer 4

from infolding of cell surface membrane, incr surface for activities eg cellular respiration

Question 5

how do bacteria feed

Answer 5

extracellular digestion
- enzymes secreted out the cell, nutrients absorbed, all transport reg by cell surface mem

Question 6

how do prokaryotes divide?

Answer 6

binary fission
- DNA replicated in semi-conservative manner
- 2 DNA loops attach to cell surface membrane – CSM elongates and divides into 2 (cytokinesis)
- genetically identical daughter cells

Question 7

describe eukaryotes cell structure

Answer 7

• DNA encased in nuclear envelope (double membrane)
• cytoplasm found between nuclear membrane and CSM
• membrane-bound organelles aid compartmentalisation

Question 8

how do membrane bound organelles in eukaryotes aid in compartmentalisation?

Answer 8

• incr efficiency of metabolism – molecules close tgt, incr speed of reactions
• diff organelles kept at diff conditions, efficient reactions within a cell (compartmentalised)
• isolation of compounds – some organelles may contain enzymes/ harmful toxins
• numbers – there can be a diff no. of organelles (depending on the needs of the cell)

Question 9

isolation of compounds – lysosomes

what are lysozomes? why do they need to be isolated?

Answer 9

vesicles that contain enzymes that need to be isolated to prevent autodigestion – destruction of cell thru action of its own enzymes

Question 10

describe nucleus 7

Answer 10

• largest organelle
• location of genetic material in form of chromosomes
• nucleoplasm within nucleus
• double membrane – nuclear envelope
• pores in nuclear envelope to regulate entry and exit of subtances like mRNA
• connected to endoplasmic recticulum
• nucleolus – dense region responsible for ribosomal RNA production

Question 11

decribe ribosomes

Answer 11

• primarily protein production
• made of ribosomal RNA prod in nucleolus
• quantity depends on amt of proteins cell needs to produce
• ribosomes either membrane bound or free floating

Question 12

free ribosomes vs membrane bound ribosomes

Answer 12

free
- floating in cytoplasm
- prod proteins needed within cytoplasm
bound
- mainly on RER
- proteins are packaged in other organelles and exported out the cell

Question 13

6 parts of endomembrane system

Answer 13

• nuclear envelope
• endoplasmic recticulum
• golgi apparatus
• lysosomes
• vacuoles
• plasma membrane

Question 14

function of RER

Answer 14

(has ribosomes)
RER involved in prod of polypeptides transported via vesicles to golgi apparatus for packaging and exported

Question 15

function of SER

Answer 15

SER involved other metabolic processes – production of enzymes needed to prod lipids and steroids, enzymes that process drugs & alcohol

Question 16

function of golgi apparatus

Answer 16

involved in further processing and packaging of molecular products of the cell
- folds and packages polypeptides tgt into functional proteins
- prodcts travel via vesicles to one side on GA
- products are processed and modified as they travel to other side
- vesicles containing final products pinch off and travel to other organelles/ cell surface for exocytosis

Question 17

function of lysosomes 5

Answer 17

membrane bound sacs containing digestive enzymes
- from golgi apparatus, w og polypeptides forming enzymes prod in RER
- presence of membrane – isolate digestive enzymes, prevent auto-digestion
- needed for digestion of food molecules taken in via phagocytosis
- used to digest worn out organelles in the cell (nutrient recycling)
- some fuse will CSM for exocytosis of enzymes

Question 18

function of contractile vacuoles

Answer 18

found in many protists (type of single celled organism)
- able to mehcanically pump water for osmoregulation

Question 19

function of large central vacuole

Answer 19

found in plant cells
- help osmoreg by buffering changes in water potential of cytoplasm
(plant cells also may contain some that store toxins or pigments)

Question 20

function of food vacuoles

Answer 20

found in many cells
- envelope food particles taken in via phagocytosis

Question 21

function of mitochondria

Answer 21

found in almost all eukaryotic cells
- responsible for cellular respiration, prod energy in form of Adenosine Tri-Phosphate (ATP)

Question 22

function of chloroplasts

Answer 22

responsible for photosyntehsis

Question 23

similarities between mitochondria and chloroplasts (3)

Answer 23

• double membrane
• not part of cellular endomembrane system
• have their own chromosomes (circular DNA)

Question 24

structure of mitochondria

Answer 24

• double membrane: smooth outer, folded inner to form cristae – incr surfac area for reactions that syn. ATP
• 2 compartments: mitochondrial matrix, intermembrane space

Question 25

mitochondrial matrix contains: 3

Answer 25

• enzymes that catalyse cellular resp processes
• ribosomes
• mitochondrial DNA

Question 26

what in the mitochondria makes ATP synthesising reactions more efficient?

Answer 26

folding of cristae (folded inner membrane) – incr surface area

Question 27

compartments in chloroplasts 2

Answer 27

• intermembrane space
• stroma

Question 28

structure and constituents of stroma 3

Answer 28

• cont enzymes, chloroplast DNA and ribosomes
• cont internal network of membranes arranged to form interconnected sacs – THYLAKOIDS
• stacks of THYLAKOIDS form a GRANUM, rich in chlorophyll

Question 29

prokaryote and eukaryote difference – ribosomes

Answer 29

pro – 70s
euk – 80s, 70s in organelles
80s larger than 70s