Biomolecules and organelles of the eukaryotic cell

Question 1

nucleus

Answer 1

contains most of the cell’s DNA, which carries the cell’s genetic information (genes)

• the genetic code is transferred via mRNA to the cytoplasm, where ribosomes translate the code into proteins
• DNA is packed into multiple, linear chromosomes
• each chromosome contains one long DNA molecule associated with many proteins, such as histones, which form nucleosomes

Question 2

nucleolus

Answer 2

dense structure in which a type of RNA called ribosomal RNA (rRNA) is synthesized

Question 3

nuclear envelope

Answer 3

double phospholipid membrane that encloses the nucleus; contains nuclear pores for transport of molecules

Question 4

role of the nucleus

Answer 4

directs protein synthesis by synthesizing messenger RNA (mRNA) (according to DNA’s instructions)
- mRNA transported to cytoplasm via nuclear pores
- ribosomes translate mRNA’s genetic message into protein (polypeptide)

Question 5

structure of DNA and RNA

Answer 5

nucleic acids store and transmit hereditary (genetic) information

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are polymers made of monomers called nucleotides, classified either as Pyrimidines (C, T, U) or Purines (A, G)

= they differ only through NITROGENOUS BASE

C & T

C & U

A & G

Question 6

double-stranded DNA

Answer 6

DNA usually consists of two strands - held together by hydrogen bonds (H) between A-T and C-G pairs (basepairs)

• there are 2H bonds in an A-T basepair and 3H bonds in an C-G basepair
• due to this specific basepairing, the 2 strands in double-stranded DNA are said to be complementary
• the complementary strands run antiparallel with regard to each other
  
  • when one strand runs 5’ → 3’, the complementary strand runs 3’ → 5’

Question 7

endoplasmic reticulum

Answer 7

consists of a network of membrane-enclosed structures (cisternae)
- the membrane is continuous with the nuclear envelope
- two types:
- smooth ER which doesn’t have ribosomes on the surface
- rough ER which has ribosomes on its surface

Question 8

functions of the ER

Answer 8

• The smooth ER is involved in the synthesis of lipids, metabolism of carbohydrates, detoxification
  of drugs and poisons.
• The rough ER is responsible for making secretory proteins (via the attached ribosomes) and for the production of membranes.

Question 9

lipids

Answer 9

group of compounds that mix poorly, if at all, with water and have many functions

• most important groups:
  
  • fats
  • phospholipids
  • steroids
• fats are constructed from 2 kinds of molecules: glycerol (3-carbon alcohol) and 3 fatty acids (16- to 18-carbon chains)

Question 10

phospholipids

Answer 10

types of lipids similar to fats but only have two instead of three fatty acids attached to glycerol

the 3rd -OH (hydroxyl) group of glycerol is joined to a negatively charged phosphate group, connected to an additional small charged or polar molecule (R)

Question 11

Golgi apparatus

Answer 11

stack of membranes that processes and packages proteins and lipids made in the ER for export to other locations inside or outside of the cell

Question 12

exocytosis

Answer 12

process by which cells move materials out of the cell; occurs through fusion of membrane-enclosed vesicle with the plasma membrane

Question 13

endocytosis

Answer 13

process by which cells move material into the cell, by pinching this material inward from the plasma membrane

Question 14

lysosomes

Answer 14

a vescicle with enzymes that digest macromolecules - they are ‘floating garbage disposals’

Question 15

what do lysosomes digest?

Answer 15

• stuff taken into the cell by phagocytosis
  
  • intracellular material that needs to be discarded (autophagy)

Question 16

endosymbiotic theory

Answer 16

~2 billion years ago

1. infoldings in the plasma membrane of an ancestrial prokaryote gave rise to endomembrane components, including a nucleus and endoplasmic reticulum
2. in first endosymbiotic event, the ancestral eukaryote consumed aerobic bacteria that evolved into mitochondria
3. in a second endosymbiotic event, the nearly eukaryote consumed photosynthetic bacteria that evolved into chloroplasts

Question 17

mitochondria

Answer 17

responsible for aerobic (O2 dependent) cellular respiration:

• conversion of the chemical energy stored in food into the energy storage molecule ATP (adenosine triphosphate) in a series of chemical reactions

Question 18

sugars (carbs)

Answer 18

fuel + building material

• monosachharides generally have molecular formulas that are some multiple of the unit CH2O
  
  • glucose (C6H12O6) is the most important monosaccharide of life

in plants, G3P is converted into:
- glucose (fuel in cellular respiration)
- sucrose (glucose + fructose)
- starch (energy storage)

Question 19

peroxisomes

Answer 19

membrane enclosed organelles that perform key roles in lipid metabolism and conversion of harmful reactive oxygen species

Question 20

cytoskeleton and centrosome

Answer 20

plays a major role in organizing the shape, structures and activities of the cell

• It allows vesicles and other organelles to “walk” along the tracks provided by the cytoskeleton
• It is composed of three types of molecular structures:
  
  • microtubules
  • intermediate filaments
  • microfilaments (actin filaments)

Question 21

microtubules

Answer 21

long and stiff tubes consisting of the protein tubulin

• in animal cells, they grow out of the centrosome, creating a transport system of tracks within the cell
• they can also form stable structures (cillia and flagella)

Question 22

ribosome

Answer 22

protein factory, consisting of RNA and proteins, free in the cytosol or bound to rER - they translate mRNA’s genetic message into proteins

Question 23

proteins

Answer 23

polymers composed of 20 different monomers (amino acids)
- amino acids only differ in the structure of their side chain (R group)