2.1- ultra structure of eukaryotic cells: membrane bound organelles

Question 1

What are animals, plants, fungal and protoctist cell?

Answer 1

Eukaryotic

Question 2

What do eukaryotic cells have?

Answer 2

• A nucleus surrounded by a nuclear envelope, containing DNA organised and wound into linear chromosomes.
• An area inside the nucleus called the nucleolus, containing RNA, where chromosomes unwind; the nucleolus is also involved in making ribosomes.
• Jelly like cytoplasm in which organelles are suspended
• A cytoskeleton- a network of protein filaments (Actin or microtubules) within the cytoplasm that move organelles from place to place within the cell; allow some cells (amoebae and lymphocytes) to move; and allow contraction of muscle cells.
• A plasma membrane
• Membrane-bound organelles other than the nucleus such as mitochondria, the Golgi apparatus and endoplasmic reticulum
• Small vesicles
• Ribosomes, which are organelles without membranes where protein are assembled.

Question 3

What are cells?

Answer 3

Cells are unit/ building blocks of all living organisms

Question 4

What do most eukaryotic cells have and what does it do?

Answer 4

Most eukaryotic cells are covered in membranes. This separates each organelle from the rest of the cell, so that it is a discrete compartment.

Question 5

What has the electron microscope enabled?

Answer 5

It has enabled scientist to ascertain the structure of these organelles by making and examining several sections through an organelle in order to build up a 3D picture of it. Biochemistry research has enabled scientists to find the functions of each organelle.

Question 6

What is the structure of a nucleus?

Answer 6

• The nucleus is surrounded by a double membrane called the nuclear envelope. There are pores in the nucleus envelope.
• The nucleolus does not have a membrane around it. It contains RNA.
• Chromatin is the genetic material, consisting of DNA wound around histone proteins. When the cell is not dividing chromatin is spread out or extended. When the cell is about to divide, chromatin condenses and coils tightly into chromosomes. These make up nearly all the organism’s genome.

Question 7

What is the function of the nucleus?

Answer 7

• The nuclear envelope separates the contents of the nucleus from the rest of the cell.
• In some regions the outer and inner nuclear membrane fuse together. At these points some dissolved substances and ribosomes can pass through.
• The pores enable larger substances such as messenger RNA (mRNA) to leave the nucleus. Substances such as some steroid hormones, any enter the nucleus from the cytoplasm via these pores.
• The nucleolus is where ribosomes are made.
• Chromosomes contain the organisms genes

Question 8

Give a summary of the function of a nucleus:

Answer 8

The nucleus:

• Is the control centre of the cell
• Stores the organisms genome
• Transmits genetic information
• Provides the instructions for protein synthesis

Question 9

What is the structure of rough endoplasmic reticulum?

*RER

Answer 9

• This is a system of membranes, containing fluid- filled cavities (cisternae) that are continuous with nuclear membrane.
• It’s coated with ribosomes

Question 10

What is the function of rough endoplasmic reticulum?

*RER

Answer 10

• RER is the intracellular transport system: the cisternae form channels for transporting substances from one area of a cell to another.
• It provides a large surface for ribosomes, which assembles amino acids into proteins. These proteins then actively pass through the membranes into the cisternae and are transported to the Golgi apparatus for modification and p[reparation,.

Question 11

What is the structure of smooth endoplasmic reticulum?

*SER

Answer 11

• This is a system of membranes, containing fluid- filled cavities (cisternae) that are continuous with nuclear membrane.
• There are no ribosomes on its surface

Question 12

What is the function of smooth endoplasmic reticulum?

Answer 12

• SER contains enzymes that catalyse reactions involved with lipid metabolism such as:
• synthesis of cholesterol
• synthesis of lipids/phospholipids needed by the cell
• synthesis of steroid hormones

It’s involved with absorption, synthesis and transport of lipids (from the gut)

Question 13

What is the structure of the Golgi apparatus?

Answer 13

• This consists of a stack of membrane bound flattened sacs. Secretory vesicles bring materials to and from the Golgi apparatus.

Question 14

What is the function of the Golgi apparatus?

Answer 14

• Proteins are modified for examples by:
• adding sugar molecules to make glycoproteins
• adding lipid molecules to make lipoproteins
• being folded into their 3D shape
• The proteins are packaged into vesicles that are pinched off and then:
• stored in the cell or
• moved to the plasma membrane, either to be incorporated into the plasma membrane, or exported outside the cell.

Question 15

What is the structure of the mitochondria (singular: mitochondrion)?

Answer 15

• These may be spherical, rod shaped or branched and are 2-5um long.
• They are surrounded by two membranes with a fluid filled space between them. The inner membrane is highly folded unto cristae.
• The inner part of the mitochondrion is a fluid filled matrix.

Question 16

What is the function of the mitochondria (singular: mitochondrion)?

Answer 16

• Mitochondria are the site of ATP (energy currency) production during aerobic respiration.
• They are self- replicating, so more can be made if the cell’s energy need increase.
• They are abundant cells where much metabolic activity takes place, fro example in liver cells and at synapses between neurones where neurotransmitter is synthesised and released.

Question 17

What are the structure of chloroplasts?

Answer 17

• They are large organelles
• They are found only in plant cells and in some protoctist.
• They are surrounded by a double membrane or envelope. The inner membrane is continuous with stacks of flattened membrane sacs called thylakoids(resembling piles of plates), which contain chlorophyll. Each stack or pile of thylakoids is called a granum. The fluid filled matrix is called the stoma.
• Chloroplasts contain loops of DNA and starch grains.

Question 18

What is the function of chloroplasts?

Answer 18

• Chloroplast are the site of photosynthesis.
• The first stage of photosynthesis, when light energy is trapped by chlorophyll and used to make ATP, occurs in the grana. Water is also split to supply hydrogen ions.
• The second stage, when hydrogen reduces carbon dioxide, using energy from ATP, to make carbohydrates, occurs in the stroma. Chloroplasts are abundant in leaf cells, particularly the palisade mesophyll layer.

Question 19

What is the structure of vacuole?

Answer 19

The vacuole is surrounded by a membrane called the tonoplast and contains fluid.

Question 20

What is the function of vacuole?

Answer 20

Only plants cells have a large permanent vacuole.

• It is filled with water and solutes and maintains cell stability, because when full it pushes against the cell wall, making the cell turgid.
• If all the plant cells are turgid then this helps to support the plant, especially in non- woody plants.

Question 21

What is the structure of lysosomes?

Answer 21

• These are small bags formed in the Golgi apparatus. Each is surrounded by a single membrane.
• They contain powerful hydrolytic (digestive) enzymes.
• -they are abundant in phagocytic cells such as neutrophils and macrophages (types of white blood cells) that can ingest and digest invading pathogens such as bacteria.

Question 22

What is the function of lysosomes?

Answer 22

• Lysosomes keep the powerful hydrolytic enzymes separate from the rest of the cell.
• Lysosomes can engulf old cell organelles and foreign matter, digest them and return the digested components to the cell for reuse.

Question 23

What is the structure of cilia and undulipodia?

Answer 23

• These are protrusions from the cell and are surrounded by the cell surface membrane.
• Each contains microtubules
• They are formed from centrioles.

Question 24

What is the function of cilia and undulipodia?

Answer 24

The epithelial cells lining your airways each have many hundreds of cilia that beat and move the band of mucus.

• Nearly all cell types in the body have one cilium that acts as an antenna. It contains receptors and allows the cell to detect signals about its immediate environment.
• The only type of human cell to have an undulipodium enables the spermatozoon to move.