cellular components

Question 1

describe the structure of the nucleus

Answer 1

• surrounded by a nuclear envelope, a semipermeable double membrane
• nuclear pores allow substances to enter/exit
• dense nucleolus made of RNA and proteins

Question 2

describe the function of the nucleus

Answer 2

• contains DNA coiled around chromatin into chromosomes
• controls cellular processes: mitosis, semi-conservative replication, mRNA transcription, gene expression etc.

Question 3

describe the structure and function of the endoplasmic reticulum

Answer 3

• cisternae: network of tubules and flattened sacs that extends from the cell membrane and connects to the nuclear envelope
• two types:
  . rough (RER): has many ribosomes attached for protein synthesis and transport
  . smooth (SER): lipid synthesis

Question 4

describe the structure and function of the golgi apparatus

Answer 4

• planar stack of membrane-bound flattened sacs
• ‘cis’ face aligns with the RER and vesicles form new layers, ‘trans’ face is where vesicles bud off via exocytosis
• molecules are processed in the cisternae
• modifies and packages proteins for export
• synthesises glycoproteins

Question 5

describe the structure and function of ribosomes

Answer 5

• formed of protein and rRNA
• two subunits: large - joins amino acids, small - has mRNA binding site

Question 6

describe the structure of a mitochondrion

Answer 6

• surrounded by a double membrane
• folded inner membrane forms cristae: site of electron transport chain
• fluid matrix; contains mitochondrial DNA, respiratory enzymes, lipids and proteins

Question 7

state the function of mitochondria

Answer 7

site of aerobic respiration to produce ATP

Question 8

describe the structure of a chloroplast

Answer 8

• vesicular plastid with double membrane
• contain thylakoids: flattened discs that stack to form grana, contains photosystems with chlorophyll
• intergranal lamellae; tubes that attach to thylakoids in adjacent grana
• contain stroma - fluid filled matrix

Question 9

state the function of chloroplasts

Answer 9

site of photosynthesis to convert solar energy into chemical energy

Question 10

describe the structure and function of a lysosome

Answer 10

• sac surrounded by single membrane
• contains embedded H+ pump that maintains acidic conditions
• contains digestive hydrolase enzymes
• glycoprotein coat protects cell interior
• fuse with other vesicles that contain something that needs to be digested e.g. bacterium
• exocytosis of digestive enzymes

Question 11

describe the structure and function of a plant cell wall

Answer 11

• made of cellulose microfibrils for mechanical support
• plasmodesmata form part of apoplast pathway to allow molecules to pass between cells
• middle lamella separates adjacent cell walls

Question 12

what are bacterial cell walls made of?

Answer 12

peptidoglycan (murein)

Question 13

what are fungal cells walls made of?

Answer 13

chitin

Question 14

describe the structure and function of centrioles

Answer 14

• spherical group of 9 microtubules arranged in triples
• located in centrosomes
• migrate to opposite poles of cell during prophase and spindle fibres form between them

Question 15

describe the structure and function of the cell surface plasma membrane

Answer 15

• ‘fluid-mosaic’ phospholipid bilayer with extrinsic and intrinsic proteins embedded
• isolates cytoplasm from extracellular environment
• selectively permeable to regulate transport of substances
• involved in cell signalling / cell recognition

Question 16

state the role of cholesterol in the cell surface membrane

Answer 16

steroid molecule that connects phospholipids and reduces fluidity

Question 17

state the role of glycoproteins in the cell surface membrane

Answer 17

cell signalling, cell recognition (antigens) and binding cells together

Question 18

state the role of glycolipids in the cell surface membrane

Answer 18

cell signalling and cell recognition

Question 19

describe the structure and function of flagella

Answer 19

• hollow helical tube made of the protein flagellin
• rotates to propel the organism

Question 20

describe the structure and function of cilia

Answer 20

-hair-like protrusions on eukaryotic cells
- move back and forth rhythmically to sweep foreign substances e.g. dust or pathogens away, or enabling the cell to move

Question 21

why is the cytoskeleton important?

Answer 21

• provides mechanical strength
• aids transport within cells
• enables cell movement

Question 22

describe the process of production of proteins

Answer 22

1. DNA is transcribed in the nucleus and converted to mRNA
2. mRNA strand leaves the nucleus via a nuclear pore
3. mRNA attaches to ribosomes on the RER where the code is read and translate into an amino acid sequence
4. amino acid sequence is transported to the golgi apparatus where it is modified and packaged into a protein
5. this protein is then transported via secretory vesicles to the cell surface membrane - this movement is aided by the cytoskeleton
6. vesicle fuses with cell surface membrane and protein is secreted via exocytosis