eukaryotic cells

Question 1

what is the structure of the nucleus

Answer 1

• 10μm in diameter - largest organelle present in all eukaryotic cells
• contains DNA
• contains a smaller spherically densely stained nucleolus (1mm diameter)
• made of RNA and proteins assemble ribosomes
• surrounded by a double membrane called the nuclear envelope (has pores)

Question 2

what is the role of the nucleus

Answer 2

• stores genetic information
• site of transcription, allows diffusion of mRNA through nuclear pores into cytoplasm
• Nucleolus: produces ribosomes
• site of mitosis/meiosis
• controls cellular processes

Question 3

what is the structure and role of ribosomes

Answer 3

ribosomes made of mRNA and protein
organelles that do not have a cell membrane
protein synthesis (translation) occurs here
have a large subunit which joins amino acids and small subunit with mRNA binding site

Question 4

describe the process of protein synthesis, transport and modification in a cell

Answer 4

DNA is transcribed in the nucleus to produce mRNA
mRNA diffuses through the nuclear pores into the cytoplasm and binds to the ribosomes on the RER
mRNA is translated into a protein
if it is to be modified, it is enclosed into a transport vesicle
the transport vesicle buds of the RER and fuses with the Golgi apparatus
it is modified - carbohydrate added to make glycoprotein or modified into a lysosome
the modified protein is enclosed into a secretory vesicle
secretory vesicle moves along the cytoskeleton
secretory vesicle fuses with the cell surface membrane and releases contents out the cell via exocytosis
exocytosis requires ATP - provided by the mitochondria

Question 5

what are 3 features that categorise a cell as a eukaryote

Answer 5

nucleus
membrane bound organelles
80s ribosomes

Question 6

what are the 3 organelles with a double membrane

Answer 6

nucleus
chloroplasts
mitochondria

Question 7

what organelles have a single membrane surrounding them

Answer 7

RER
SER
lysosome

Question 8

what are the two types of endoplasmic reticulum

Answer 8

rough endoplasmic reticulum
soft endoplasmic reticulum

Question 9

describe the structure of rough endoplasmic reticulum

Answer 9

network of tubules of flattened membranes (cisternae) joined together and attached to nuclear envelope

Question 10

describe the role of rough endoplasmic reticulum

Answer 10

covered in ribosomes, small organelles
to synthesis, store and transport proteins

Question 11

what is the difference between RER and SER

Answer 11

RER contains ribosomes
SER does not contain ribosomes

Question 12

what is the structure of SER

Answer 12

network of tubules of flattened membrane (cisternae) without ribosomes

Question 13

what is the function of soft endoplasmic reticulum

Answer 13

`store, transport and synthesis lipids (fats/steroids)

Question 14

describe the structure of a mitochondrion

Answer 14

surrounded by a double membrane
foled inner membrane form cristae - site of eletron transport chain
fluid matrix - contain mitochondrial DNA, respiratory enzymes, lipids, proteins

Question 15

describe the role of mitochondria

Answer 15

site of aerobic respiration using respiratory substances - glucose releasing ATP
ATP uses for metabolic activity
cell division, protein synthesis (supporting cell growth) and muscle contraction

Question 16

describe the components of the mitochondria

Answer 16

double membrane - permeable and control the entry and exit of material
the inner of the two membranes is folded to form extensions know as cristae
cristae - extension of the inner membrane
provide a large surface area for the attachment of enzymes and other proteins involved in respiration (site of respiration)
matrix - makes up the reminder of the mitochondrion
contains proteins, lipids, 70s ribosomes and free circular DNA that allows the mitochondria to control the production of some of their own proteins
many enzymes involved in respiration are found in the matrix

Question 17

in cells that are active e.g muscle cells how would the mitochondria be different

Answer 17

the number and size of the mitochondria and the number of their cristae are high in cells that have a high level of metabolic activity

Question 18

what is the structure and function of the golgi apparatus

Answer 18

stacks of membrane (cristernae) surrounded by lamellae not joined together
its function is to modify, package and transport proteins and lipids

Question 19

describe the structure of a chloroplasts

Answer 19

vesicular plastid with double membrane
membrane-bound compartments called thylakoids containing chlorophyll stack to form stuctures called grana
grana are joined together by lamellae (thin and flat thylakoid membranes)
stroma is a fluid-filled matrix
contain small circular pieces of DNA and ribosomes (70s) use to synthesis proteins needed in chloroplast replication and photosynthesis

Question 20

what is the function of chloroplasts

Answer 20

the site of photosynthesis:
the light-dependent stage takes place in the thylakoids
the light-independent stage takes place in the stroma

Question 21

function of lysosomes

Answer 21

specialist forms of vesicles which contain hydrolytic enzymes - break down biological molecules
break down waste materials such as worn-out organelles
used extensively by cells of the immune system and in apoptosis (programmed cell death)

Question 22

what is the structure of the centriole

Answer 22

hollow fibres of microtubules
two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division
not found in flowering plants and fungi
migrate to opposite poles of cells during prophase and spindle fibres form between them

Question 23

what is the structure of the microtubule

Answer 23

found in all eukaryotic cells
makes up the cytoskelton of the cell and about 25nm in diameter
made of α and β tubulin combined to form dimers, the dimers are then joined into protofilaments
thirteen protofilaments in a cylinder make a microtubule