Organelles

What are the 2 types of cell that we need to know about?

• Eukaryotic - you for your cells (animal and plants)

• Prokaryotic - Bacterial cells

What are the structures in a eukaryotic cell which have membranes?

• Plasma membrane

• Golgi apparatus

• Nucleus

• Nucleolus

• Mitochondria

• Rough endoplasmic reticulum (RER)

• Smooth endoplasmic reticulum (SER)

• Lysosomes

• Chloroplasts

• Cilia

• undulipodia

• Vacuole

What structures make up the nucleus?

• Nuclear envelope - double membrane

• Nuclear pores

• Nucleoplasm - Jelly like material

• Chromosomes - Protein bound, linear DNA

• Nucleolus - Small sphere inside of the nucleus

What is the function of the nuclear envolope?

• Separates the contents of the nucleus from the rest of the cell

• What is the function of the Nucleolus?

• It is where rRNA is made

• It is where ribosomes are made

What is the function of the Nuclear pores?

• They allow for substances to leave and enter the nucleus

• Leave:

  • mRNA

  • Ribosomes

• Enter:

  • Steroid hormones

What is the function of the nucleoplasm?

• To hold genetic coding for each cell - Chromosomes

What are the 4 functions of the nucleus?

• rRNA synthesis

• Ribosome synthesis

• Holding genetic material

• The site for DNA replication

• Controls the activities the cell

How is DNA packed so tightly?

• Because they are in Chromatins which are wound around histone proteins

Describe the structure of the Rough endoplasmic reticulum(RER)?

• A system of membranes, which contain fluid-filled cavities(cisternae) that are continuous with the nuclear membrane

• It is coated in ribosomes

Describe and explain is the function of rough endoplasmic reticulum (RER)?

• It is the intracellular transport system:

  • the cisternae form channels for transporting substances from one area of the cell to another

• It provides a large surface area for ribosomes:

  • They assemble amino acids into proteins

  • These proteins actively pass through the membrane into the cisternae what are transported to the Golgi apparatus

What is the Smooth endoplasmic reticulum(SER)?

• It is a system of membranes, containing fluid-filled cavities(cisternae) that are continuous with the nuclear membrane

• There are no ribosomes on the surface

What are the functions of the smooth endoplasmic reticulum(SER)?

• Contain enzymes that catalyse reactions involved with lipid metabolism:

  • Synthesis of cholesterol

  • Synthesis of lipids/phospholipids needed in the cell

  • Synthesis of Steroid hormones

• It is involved with absorption, synthesis and transport of lipids(from the gut)

What is the structure of the Golgi apparatus?

• It consists of a stack of membrane-bound flattened sacs.

• Secretory vesicles bring materials to and from the Golgi apparatus

What are the functions of the Golgi apparatus?

• Proteins are modified in the Golgi apparatus, for example by:

  • Adding sugar molecules to make glycoproteins

  • Adding lipid molecules to make lipoproteins

  • Being folded into their 3D Shape

• The Golgi apparatus packages proteins into vesicles which are pinched off and then:

  • Stored in the cell or

  • Moved to the plasma membrane, wither to be incorporated into the plasma membrane, or exported outside of the cell

What is the structure of a mitochondrion?

• They may be spherical, rod shaped or branched and are 2-5 micrometres long

• They are surrounded by 2 membranes with a fluid-filled space between them called the intermembrane space:

  • The inner membrane

  • The outer membrane

• The inner membrane is highly folded into cristae

• The inner per of the mitochondrion is a fluid-filled matrix

What are the functions of mitochondria?

• The site of ATP production during aerobic respiration

• Self-replicating, so more can be made if the cell’s energy needs increase

• Abundant in cells where a lot of metabolic activity take place:

  • Liver cells

  • Synapses between neurons where neurotransmitter is synthesised and released

  • Muscle cells

What is the structure of lysosomes and what do they contain?

• They are small bags, which are formed from the Golgi apparatus

• Each lysosome is surrounded by a single membrane

• They contain powerful hydrolytic(digestive)enzymes

• They are abundant in phagocytic cells such as:

  • Macrophages

  • Neutrophils

What are the functions of lysosomes?

• Lysosomes keep the powerful hydrolytic enzymes separate from the rest of the cell

• Phagocytic cells can ingest or digest invading pathogens

• Recycling - Lysosomes can engulf old cell organelles and foreign matter, digest the and return the digested components to the cell for reuse

What is the structure of chloroplasts and what is it made of?

• Large organelles: 4-10 micrometres long

• They are surrounded by a double membrane or envelope

• It is made of an:

  • Inner membrane which is continuous with thylakoids, which contain chlorophyll

  • Each stake or pie of thylakoids is called a granum

  • There is a fluid-matrix called stroma

  • They also contain intergranal lamellae

  • In-between the inner and outer membrane there is a intermembrane compartment

What does the stroma contain?

• loops of DNA, starch, ribosomes and lipids(enzymes)

What is the function of chloroplasts?

• The site of photosynthesis

What is the structure of Vacuoles?

• It is surrounded by a membrane called the tonoplast, and contains fluid

What are vacuoles in plants called?

• Permanent vacuoles

What is the function of the vacoule?

• Holds water and solutes

• It makes the cell turgid:

  • When the vacuole is full it pushes against the cell wall

What is the structure of cilia?

• They are small hair like protrusions from the cell are surrounded by the cell surface membrane

• They contain microtubes which are in a 9+2 arrangement

What is the function of cilia?

• The epithelial cell which lines the air way each have many hundreds of cilia which beat and move mucus

• Nearly all cell types in the body has 1 cilium that acts as an antenna. It contains receptors and allows the cell to detect singles about its immediate environment

What is the structure of undulipodia?

• It is a tail protruding from the cell and is surrounded by the cell surface membrane

• They contain microtubules in a 9 + 2 formation

What are both cilia and undulipodia formed from?

• Centrioles

What is the structure of ribosomes, what are they made of and where are they located?

• Structure:

  • Small spherical organelles, about 20 nanometres in diameter

• Formation:

  • Made of ribosomal DNA

  • Made in the nucleolus, as 2 separate subunits, which combine after passing through the nuclear envelope

• Location

  • some remain in the cytoplasm and some attach to the RER

What are the 2 sub-units of ribosomes?

• 70s and 80s

What are the functions of ribosomes?

• They are for protein synthesis

What s the structure of centrioles?

• Consist of 2 bundles of microtubules at right angle to each other.

• The microtubules are made of tubulin proteinn subunits and are arranged in a cylinder

• The micro tubules are arranged in microtubule triplets

What are the functions of centrioles?

• In cell division:

  • Before cell division, The spindle, which are made of threads of tubulin, forms from the centrioles

  • Chromosomes attach to the middle part of the spindle and then motor proteins walk along the tubulin threads which pull the chromosomes to opposite ends of the cell

• Formation of cilia and undulipodia

  • Before the cilia form, the centrioles multiply and line up beneath the cell surface membrane

  • Microtubules then sprout outwards from each centriole forming a cilium or an undulipodium

Are centrioles present in plants?

• No

What is the cytoskeleton?

• A network of protein structures within the cytoplasm

What are the 3 types of protein structures of cytoskeleton and what is their structure?

• Microfilaments:

  • Rod-like microfilaments which is a polymer of the monomer actin

  • About 7nm is diameter

• Intermediate filaments:

  • About 10 nm is diameter

• Microtubules

  • Straight and cylindrical, made of protein subunits called tubulin

  • About 18-30 nm in diameter

What is present on the cytoskeletons

• Enzymes called Cytoskeletal motor proteins

What is the energy source of cytoskeletal motor proteins and how is it formed?

• ATP

• Formed by hydrolysing ATP after binding onto its active site

What are the 3 cytoskeletal motor proteins?

• Myosin

• Kinesin

• Dynein

What is the function of cytoskeleton microfilaments?

• They give support and mechanical strength

• They keep the cell’s shape stable an

• Allow cell movement

What are the functions of cytoskeletal microtubules?

• Provide shape and support to cell

• Help substances and organelles to move through the cytoplasm within the cell

• They form a track which motor proteins can walk along and drag organelles from one part of the cell to the other

• They form spindle before cell division

• They form cilia and undulipodia

What is the function of cytoskeletal intermediate filaments ?

• They anchor the nucleus within the cytoplasm

• They extend between cells in some tissue, which enables cell-cell signalling

What is the structure of the cell wall?

• In plants it is on the outside of the plasma membrane

• It is made from bundles of cellulose fibres which are perpendicular to each other

What is the function of cell walls?

• It provides strength and prevents cells from bursting(plants-when turgid)

• Maintains cell’s shape

• Contribute to the strength and support of the whole plant

• Are permeable and allow solutions to pass through

What organisms have a cell wall?

• Fungi

• Bacteria cells

• Plant cells

What is the cell wall in fungi made of?

• Chitin

What Structures are present in plant cells but not in most animal cells?

• Vacuole

• Cell wall

• Chloroplasts

Describe how a protein is made and secreted

1. DNA is transcribed into mRNA

2. mRNA leaves the nucleus through a nuclear pore

3. The mRNA goes to rough endoplasmic reticulum and binds to a ribosome

4. The mRNA is translated by the ribosome and forms a protein

5. The protein is the packaged into a vesicle and is pinched off the RER

6. The cytoskeletal motor proteins move the vesicle towards the Golgi apparatus and fuses the Golgi apparatus

7. The protein is now in the Golgi apparatus where it is being modified

8. After modification a secretory vesicle is formed by the Golgi apparatus and is pinched off

9. The vesicle is moved towards the plasma membrane by motor proteins on the cytoskeleton and fuses to the plasma membrane - exocytosis

10. The plasma membrane opens to release the protein

What are the similarities between Prokaryotic and Eukaryotic cells?

• Both have a plasma membrane

• Both have Cytoplasm

• Both have Ribosomes for assembling amino acids into proteins

• Both have DNA and RNA

What is the difference between Prokaryotic cells and eukaryotic cells?

• Prokaryotic cells are much smaller than eukaryotic cells

• Prokaryotic cells have no nucleus - DNA is free in the cytoplasm while eukaryotic cells do

• Prokaryotic vells have no membrane bound organelles while eukaryotic have many membrane bound organelles

• Prokaryotic cells have cell wall made of peptidoglycan while eukaryotic cell walls are made from cellulose or chitin

• Prokaryotic cells have DNA is plasmids while eukaryotic cells have linear DNA

Why do prokaryotic cells have DNA in plasmids?

• Because the DNA is “naked” and so therefore it is not wound around histone proteins

What structures are present in prokaryotic cells which are not in eukaryotic cells?

• Flagellum - tails which allow bacteria to move

• Pili - Hairs which enable bacteria to adhere ti host cells or to each other. Also allow the passage of plasmid DNA from one cell to another

• Small loops of DNA called plasmids and main large ones too - Nucleoid

• A protective waxy capsule surrounding the cell

What is the endosymbiont theory?

• The theory that eukaryotes evolved from prokaryotes

How does the endosymbiont theory work?

• 1.5 - 2 billion years ago much larger prokaryotic cells engulfed smaller prokaryotic cells - some which can undergo aerobic respiration to produce ATP - mitochondria. and some which can under to photosynthesis to produce glucose - Chloroplasts

• However, instead of these cells being destroyed, increase their membrane remained intact in the cell and they survived together

• This prokaryotes have no evolved into eukaryotes

What is the evidence that this theory is true?

• Mitochondria and chloroplasts have their own DNA which is also in plasmids which are found in prokaryotic cells

• They also contained ribosomes which are also found in prokaryotic cells

• When the organelles undergo division they also divide by binary fission which is the same as prokaryotic cells