Topic 3

Question 1

Describe the structure of a prokaryotic cell

Answer 1

-Ribosomes - where 70S proteins are made

Plasmid - Double-stranded DNA in a circular structure
-Often contain additional genes that help with antibiotic resistance

• Pili - Thin, protein tubes
  - Allow bacteria to stick to surfaces

-Cytoplasm

• Flagellum - Whip-like structure that aids in movement
• Sensory structure
• Cell wall - made of peptidoglycan
• Cell surface membrane
• Nucleoid - Contains single, circular length of DNA
• Mesosome

Question 2

Describe the structure of a eukaryotic cell:

Answer 2

• Nucleus - Double membrane (envelope)
  - pores in nuclear envelope
• Nucleolus - Region of dense DNA and proteins
  - Makes ribosomes
• Rough endoplasmic reticulum - A series of single, flattened sacs enclosed by a membrane
• Ribosomes on surface
• Proteins made here
• Smooth endoplasmic reticulum - Series of single, tubular sacs made of membrane
• Lipids made here
• Mitochondria - Double membrane (envelope)
  - Inner membrane folded into cristae
  - Central area contains the matrix
  - Contains 70S ribosomes
  - Site of respiration

-Ribosomes (80S) - Site of protein synthesis

• Golgi apparatus - A series of single, curved sacs enclosed by a membrane
• Modifies proteins and packages them into vesicles for transport
• Lysosome - Enclosed by a single membrane
  - Contains digestive enzymes
  - Destroys old organelles and pathogens
• Centrioles - Two hollow cylinders
  - Arranged at right angles to each other
  - Makes the spindle during cell division

Question 3

Describe what happens in protein trafficking

Answer 3

• Amino acids made into proteins on ribosomes
• Newly made proteins stored and folded in rER cavity
• Protein packaged into vesicles at the end of the rER membrane
• Vesicles transport protein to Golgi apparatus
• Protein modified in Golgi apparatus
• Extracellular enzymes packaged into vesicles again

Question 4

Explain the roles of the rough endoplasmic reticulum and the Golgi apparatus in a cell

Answer 4

• Proteins produced by ribosomes on rough ER
• Proteins folded within rER
• Vesicles from rough ER fuse with Golgi apparatus
• Protein is modified in Golgi apparatus
• Golgi produces secretory vesicles for secretion of extracellular enzymes

Question 5

Give the structure of a sperm cell

Answer 5

• Acrosome head - Contains enzymes to digest the outer layers of the egg
• Haploid nucleus - Contains haploid number of chromosomes
• Mid region - Contains mitochondria to provide energy through respiration
• Flagellum - Aids movement (swimming)

Question 6

Describe the structure of a egg cell

Answer 6

• Haploid nucleus
• Cytoplasm - contains energy-rich material
• Cortical granules - Special vesicles
  
  • Contains substance that stops more than one sperm fertilising the egg
• Zona pellucida - Jelly layer
  - Prevents more than one sperm fertilising the egg

-Follicle cells

Question 7

Process of fertilisation:

Answer 7

-Acrosome reaction -
Front of sperm touches Zona pellucida and acrosome bursts
Enzymes released that digest a channel in the Zona pellucida

-Membrane fusion -
Surface membranes of sperm and egg fuse, allowing haploid nucleus from sperm to enter cytoplasm of egg

-Cortical reaction -
Cortical granules fuse with egg cell membrane and release contents via exocytosis
This releases a substance that causes a hardening of the Zona pellucida
This prevents other sperm from entering

-Fertilisation -
Chromosomes from haploid sperm and egg combine to restore diploid number