2.1.1 H& k EUKARYOTIC CELL STRUCTURE

Question 1

Nucleus

Answer 1

A part of the cell containing DNA and RNA and responsible for growth and reproduction

• DNA is contained within a double membrane called a nuclear envelope to protect it from damage in the cytoplasm
• Nuclear pores allow molecules to move into and out of the nucleus.
• DNA associates with proteins called histones to form a complex called chromatin (coils and condenses to form chromosomes)

Question 2

Nucleolus

Answer 2

Found inside the nucleus and produces ribosomes

• composed of proteins and RNA. RNA is used to produce ribosomal RNA (rRMA) which is then combined with proteins to form ribosomes necessary for protein synthesis

Question 3

Mitochondria

Answer 3

Powerhouse of the cell, organelle that is the site of ATP (energy) production

• double membrane with a highly folded structure called cristae and a fluid interior called the matrix
• mitochondrial (mt)DNA in small amounts

Question 4

Ribosomes

Answer 4

complexes that make proteins; free in cytosol or bound to rough ER or nuclear envelope

1. 80S eukaryotic cells
2. 70S prokaryotic cells

Question 5

Vesicles

Answer 5

membranous sacs, store or transport substances

• transport materials inside the cell

Question 6

Lysosomes

Answer 6

An organelle containing digestive enzymes

• specialised forms of vesicles that contain hydrolytic enzymes
• they break down waste material in cells in old organelles and play important role in the immune system
• play an important role in programmed cell death (apoptosis)

Question 7

Cytoskeleton

Answer 7

A network of fibers that holds the cell together, helps the cell to keep its shape, and aids in movement

3 components: microfilaments, microtubules, intermediate fibres

Question 8

Microfilaments

Answer 8

Long, thin fibres that function in the movement and support of the cell

• responsible for cell movement & cell contraction during cytokinesis

-made of actin

Question 9

Microtubules

Answer 9

globular tubilun proteins polymerise to form tubes that are used to form a scaffold-like structure that determines the shape of a cell

• acts as tracks for the movement of organelles
• spindle fibres, which have a role in the physical segregation of chromosomes in cell division are composed of microtubules

Question 10

Intermediate fibres

Answer 10

Give mechanical strength to cells and help maintain their integrity

Question 11

Centrioles

Answer 11

a minute cylindrical organelle near the nucleus in animal cells, occurring in pairs and involved in the development of spindle fibres in cell division.

• composed of microtubules where two associated centrioles form a centrosome
• centrosome is involved in the assembly and organisation of the spindle fibres

Question 12

Flagella

Answer 12

extension that protrude from certain cell types

• enables cell mobility and can be used as a sensory organelle detecting chemical changes

Question 13

Cilia

Answer 13

Hairlike projections that extend from the plasma membrane and are used for locomotion

• stationary: present on surface of cells and have important sensory functions
• mobile: beat in a rhythmic manner creating a current and helps move substances away

Question 14

Cell membrane (plasma membrane)

Answer 14

phospholipid bilayer that surrounds all cells and regulates what enters and leaves the cell

• proteins also totally penetrate and appear on the inner and outer surfaces
• main function: act as a boundary between the cell and its environment (controls entry and exit= selectively permeable)

Question 15

Endoplasmic Reticulum

Answer 15

network of membranes enclosing flattened sacs called cisternae

• Smooth/ Rough endoplasmic reticulum

Question 16

Smooth Endoplasmic Reticulum

Answer 16

An endomembrane system where lipids are synthesised, calcium levels are regulated, and toxic substances are broken down.

• contain enzymes important in the synthesis of steroid hormones and detoxifying drugs
• stores calcium ions important in muscle contractions and secretion of vesicles

Question 17

Rough Endoplasmic Reticulum

Answer 17

An endomembrane system covered with ribosomes where many proteins for transport are assembled.

-Transport vesicles bud from the ER keeping secretory proteins separate when in transit from one part o the cell to another

Question 18

Golgi apparatus

Answer 18

A system of membranes that modifies and packages proteins for export by the cell

• products of endoplasmic reticulum are modified and stored

-cis face receiving department and trans face shipping department

Question 19

protein production

Answer 19

1. Nucleus- Transcription- DNA is converted to mRNA and is sent out of the nucleus into cytoplasm via the nuclear pores
2. Ribosomes on RER- mRNA attaches to the ribosomes and proteins are made (translation)
3. RER- proteins are folded and processed in the RER. then they are transported from the RER to the cis face of the Golgi apparatus in vesicles
4. Golgi apparatus- proteins may undergo further processing (e.g sugar chains are trimmed or more are added)
5. Proteins leave the Golgi apparatus from the transface in the secretory vesicles
6. Secretory take the finished proteins to the plasma membrane where they undergo exocytosis and leave the cell