Lecture 5&6 - Cell Structure & Function

Question 1

What is the most prominent structure in eukaryotic cells?

Answer 1

Nucleus

Question 2

Where is rRNA synthesised, precisely

Answer 2

Nucleolous

Question 3

What is the role of the nuclear pores?

Answer 3

allow exchange of material between the nucleus and cytoplasm

Question 4

What is chromatin?

Answer 4

Uncondensed form of DNA associated with histone proteins (in eukaryotes) and contains some RNA

Question 5

how many layers of phospholipids does the nuclear membrane have?

Answer 5

4 (2 bilayers) It is a double membrane

Question 6

What is the nuclear pores lined up with?

Answer 6

a complex of 8 proteins

Question 7

What is the analog of cytoplasm in the nucleus?

Answer 7

Nucleoplasm

Question 8

What is the function of genes?

Answer 8

Small sections of DNA that usually code for proteins, sometimes RNA(rRNA)

Question 9

What is the unit of heredity?

Answer 9

genes

Question 10

What are the differences in the structure of free and bound ribosomes?

Answer 10

there is no difference in structure

Question 11

What is the function of free ribosomes?

Answer 11

make proteins that function in the cell (work Intracellularly) Eg; enzymes that catalyze first steps of sugar breakdown

Question 12

what is the relation between protein synthesis and ribosomal count?

Answer 12

directly proportional

Question 13

What are the structural differences between ER and Golgi body?

Answer 13

• ER is continuous with nucleus, Golgi body is NOT
• ER are physically connected, Golgi body has separate stacks of 3-20 cisternae (both Have cisternae)

Question 14

Describe the steps of protein synthesis

Answer 14

• mRNA is synthesised from DNA in the nucleus
• mRNA exits via nuclear pores to the ribosome
• at ribosome mRNA contains the code to make proteins while tRNA comes to the ribosome with the amino acid corresponding to the codon (triplet)-
• polypeptide chain stops building when STOP codon is reached

Question 15

describe the steps of ribosomal synthesis

Answer 15

• rRNA is synthesised in the nucleolous using DNA
• Combine with protein molecules imported from cytoplasm, now exist as subunits
• small and large subunits exit the nucleus via nuclear pores
• Small and large subunits combine in the cytoplasm

Question 16

What are the functions of the smooth ER?

Answer 16

• Metabolism of carbohydrates
• synthesis of lipids (including phospholipids and steroids)
• Detoxification of drugs and poison
• storage of Ca2+

*Actual function in the cell depends on requirement and tissue function eg; in liver, detoxification

Question 17

How does the ER grow?

Answer 17

by adding membrane proteins and phospholipids into it’s own membrane

Question 18

Describe the ER

Answer 18

• the membrane factory of the cell
• Consists of flattened sacs called cisternae
• interconnected tubules( even rough and smooth)
• Continuous with nuclear membrane
• has a space in middle called ER lumen or cisternal space

Question 19

which chromosome is larger, X or Y

Answer 19

Female X is larger

Question 20

what is the function of the Golgi apparatus?

Answer 20

• Modification of products coming from ER such as proteins and phospholipids eg; modification of first carbohydrates attached to protein
• Removes sugar monomers and substitutes others
• makes its own polysaccharides
• may even modify lysosomes in animal cells

Question 21

What are lysosomes ?

Answer 21

Membranous sac of hydrolytic enzymes that an animal cells use to digest macromolecules Plant cells do not have lysosomes

have very low PH

help out in phagocytosis in cells such as macrophages

Question 22

What is autophagy?

Answer 22

recycling cell’s own organic material using lysosomes

Question 23

Which face of the Golgi apparatus points towards the ER?

Answer 23

Cis face