Cell organelles Flashcards
describe what can happen if a protein has folded
It can be modified further once it has folded
e.g. some proteins have carbohydrate molecules attached to them - forming glycoproteins - these modifications are critically important for the function of these proteins
role of nucleus
manufacture ribosomal RNA and ribosomes
retain the genetic material of the cell in the form of DNA and chromosomes
act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
where does translation take place
Translation takes place on a ribosome
state different destinations of proteins
different proteins have different destinations
some proteins function in the cytoplasm
other proteins are sent to different organelles e.g. certain digestive enzymes are sent to lysosomes
some proteins are inserted into the cell membrane for example receptor proteins
other proteins are secreted from the cell such as hormones or antibodies
Which organelles is involved int eh targeting of different proteins to different destinations
how proteins are targeted to different destinations is complex. A LOT OF THIS TARGETTING INVOLVES THE ROUGH ENDOPLASMIC RETICULUM and the Golgi apparatus
what do ribosomes consist of, and what are they called]
draw the structure of a ribosome
Ribosomes consist of two subunits - large sub unit and small subunit
https://www.medschoolcoach.com/wp-content/uploads/2022/12/RibosomeStructureFunction-Figure1.jpg
What does each subunit include
Each subunit contains a number of different proteins plus ribosomal RNA
IN cells, where are a large number of ribosomes found
In any cell, a large number of ribosomes are found in the cytoplasm
State the function of ribosomes found in the cytoplasm
Ribosomes found in the cytoplasm translate proteins which remain the cytoplasm
If not found in the cytoplasm, where are other ribosomes found
Other ribosomes are found attached to the rough endoplasmic reticulum
Describe the structure of the Rough ER
The Rough Endoplasmic Reticulum consists of sheets of membranes forming flattened sacs called cisternae
These cisternae contain a range of different enzymes
The membranes of the cisternae are covered with ribosomes
These ribosomes are where translation takes place for proteins which are secreted from the cell, as well as proteins for the cell membrane and for lysosomes
proteins are synthesised by ribosomes on the membrane of RER
Describe how a protein is transferred from the rough ER to the Golgi apparatus to out of the cell
A molecule of mRNA has attached and translation is taking place
The growing polypeptide chain passes through the membrane and into the lumen of the rough ER
In the lumen, the polypeptide chain now folds into its tertiary structure
Now the polypeptide makes its way through the rough ER. During this process, the polypeptide can be modified.
E.g. carbohydrate molecules can be added to form a glycoprotein
Finally the polypeptide is packaged into vesicles and is transported to the Golgi apparatus
The Golgi apparatus also consists of sheets of membranes forming flattened sacs called cisternae
As polypeptide makes its way through the Golgi apparatus, it can be modified further.. E.g. additional carbohydrate molecules may be attached
At some point, the polypeptide will have reached its final structure and scientists now refer to it as a functional protein
Once the protein has completed its journey through the Golgi apparatus. It is packaged into vesicles
These vesicles can then fuse with the cell membrane and the protein can be secreted from the cell
Alternatively, the protein can form part of the structure of the cell membrane
Or the proteins can enter vesicles which go on to form lysosomes
Final destination of protein depends on both amino acid sequence of protein and how the protein was modified in the rough ER and Golgi apparatus/function of protein
What feature will be present on cells which secrete large amounts of protein
Cells which secrete large amounts of protein will have a lot of rough ER
E.g. beta cells in the pancreas which make the hormone insulin
Describe the role of the RER
proteins are synthesised by ribosomes on the membrane of RER
These proteins then move through the rough ER, where they are modified e.g. carbohydrate molecule can be attached to the protein to form a glycoprotein
_____________
provide a large SA for synthesis of proteins and glycoproteins
provide a pathway for the transport of materials, especially proteins, throughout the cell
Describe the structure/role of the SER
Some ER is not covered with ribosomes. This is called SER
The SER also consists of sheets of membranes forming flattened sacs called cisternae
The job of the smooth ER is to make and store both lipids and carbohydrates
These can then pass through the golgi apparatus where they can be modified and then transported to their final destinations
E.g. lipids can be transported to the cell membrane to form part of the phospholipid bilayer
-___________
TO SYNTHESISE, STORE AND TRANSPORT CARBOHYDRATES AND LIPIDS
Describe the role/structure of the Golgi Apparatus
The Golgi apparatus also consists of sheets of membranes forming flattened sacs called cisternae
As polypeptide makes its way through the Golgi apparatus, it can be modified further.. E.g. additional carbohydrate molecules may be attached
-————————-
ADD carbohydrate to proteins to form glycoproteins
produce secretory enzymes e.g. those secreted by pancreas
secrete carbs such as those used in making cell walls in plants
transport, modify and store lipids
form lysosomes
Describe the structure of lysosomes
Lysosomes contain powerful digestive enzymes such as proteases
a membrane-bound organelle that releases
hydrolytic enzymes
These digest large molecules into smaller soluble molecules
The internal fluid in a lysosome is acidic. This is because lysosomal enzymes have an optimum pH which is acidic
acidic interior
Describe the function of lysosomes
Lysosomes play a key role in phagocytosis - e.g. in white blood cells
— hydrolyse material ingested by phagocytic cells e.g. white blood cell and bacteria
first white blood cell forms a vacuole around bacteria - phagosome
Lysosomes now fuse with phagosome
Lysosomal enzymes now digest the bacteria and the soluble digestion products now pass into the cytoplasm
Lysosomes can be used to destroy organelles that are damaged or no longer functional
In this case, the organelle is surrounded by a vacuole and lysosomes fuse with the vacuole membrane
The lysosomal enzymes now digest the organelle
The digestion products are absorbed into the cytoplasm and can be reused to make new organelles
Sometimes lysosomes transfer their enzymes outside of the cell by exocytosis in order to destroy material around the celle.g. to digest and remove unwanted proteins or dead cells
hydrolyse material ingested by phagocytic cells, e.g. wblood cell and bacteria
release enzymes to the outside of the cell (exocytosis) in order to destroy material around the cell
digest worn out organelles so that the useful chemicals they are made of can be re-used
completely break down cells after they have died (AUTOLYSIS0
where is mitochondria found
Mitochondria is found in all eukaryotic organisms including animals, plants and fungi
stages of aerobic respiration
Glycolysis - occurs in cytoplasm
The Krebs Cycle
Oxidative Phosphorylation (stage in aerobic respiration which requires oxygen)
– Both occur in mitochondria
function of mitochondria
Mitochondria play a critical role in aerobic respiration to produce the energy carrying molecule ATP
describe what happens in aerobic respiration
In aerobic respiration, the carbohydrate glucose is broken down into carbon dioxide and water
The energy contained in the chemical bonds of glucose is transferred to ATP
describe the structure and function of mitochondria
Mitochondria have a double membrane
which are called the outer mitochondrial membrane and the inner mitochondrial membrane
In between these membranes there is the intermembrane space
Within the mitochondria, there is a fluid called the matrix. Enzymes for the Krebs Cycle (a stage in aerobic respiration) are found in the matrix -
contains proteins, lipids, ribosomes and DNA that allows the mitochondria to control the production of some their own proteins - MATRIX
The enzymes for oxidative phosphorylation (stage in aerobic respiration) are found on the inner mitochondrial membrane
The inner membrane is highly folded.
These folds are called cristae
By having cristae (folds in inner membrane/by folding inner membrane like this)/many folds in inner membrane, it increases the SA/means there is a large SA for the enzymes needed for oxidative phosphorylation
contain a large number of cristae. This provides an increase SA for the enzymes needed for oxidative phosphorylation
In the mitochondria, there is also a loop of mitochondrial DNA. This DNA contains the genes required for some of the enzymes involved in aerobic respiration.
gene encode some of the enzymes involved in aerobic respiration.
Mitochondria also contain mitochondrial ribosomes. These synthesise the proteins encoded by the mitochondrial DNA
where do we usually find larger numbers of mitochondria
Mitochondria play a key role in aerobic respiration.
Larger numbers of mitochondria are found in cells which require a lot of energy
E.g. muscle cells which require a lot of energy for contraction
Also mitochondria in these cells also contain a large number of cristae. This provides an increase SA for the enzymes needed for oxidative phosphorylation
Draw a mitochondria
https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/43e60419-9e81-44b5-8ac0-b2236b5f04ee/mitochondria-structure-diagram.png
add dots around surface of inner mitochondrial membrane for enzymes for oxidative phosphorylation
function of chloroplasts
the organelles where photosynthesis takes place
sites of photosynthesis
where do we find chloroplasts and where are they not found within the plant (give an example)
Chloroplasts are found in plant cells which carry out photosynthesis
They are not found in parts of the plant that do not photosynthesise e.g. the roots
describe what happens in photosynthesis
In photosynthesis, the energy from light is used to react carbon dioxide with water to form oxygen and the carbohydrate glucose
The energy that was trapped in photosynthesis is now contained within the chemical bonds in the glucose molecule
how many reactions does photosynthesis consist of
describe these reactions
Photosynthesis consists of two sets of reactions
The light-dependent reactions use chlorophyll to harvest light energy
The energy is then transferred into the chemical bonds of other molecules such as ATP
this means that light-dependent reactions only take place in the presence of light
Other set of reactions are called the light-independent reactions.
These are the reactions in which glucose is formed.
These reactions do not require light
This means that these reactions take place during both light and dark conditions
Describe the structure and function of chloroplasts
link the structures to their functions
Chloroplasts are surrounded by a double membrane (just like mitochondria)
These membranes control which molecules enter and leave the chloroplast
Inside the chloroplast, there are membrane-bound flattened discs. These discs are called thylakoids
Thylakoids are where the light-dependent reactions take place
Therefore thylakoids contain the chlorophyll and enzymes needed for the light-dependent reactions
Thylakoids are stacked on top of each other. A stack of thylakoids is called a granum
By stacking the thylakoids into grana (plural), light can be absorbed more efficiently
Thylakoids on different grana are connected to each other by flattened membranes called lamellae
The lamellae play a role in the light-dependent reactions and allow chemicals to pass between the grana
Chloroplasts contain a fluid material called the stroma. The stroma is where light-independent reactions take place
The stroma contains the enzymes needed for the light-independent reactions
The end product of photosynthesis is the carbohydrate glucose
This glucose can be converted to the polysaccharide starch which is stored in the chloroplast as starch granules
Chloroplasts also contain a loop of DNA (like mitochondria) - chloroplast DNA. This DNA contains the genes which encode some of the proteins needed for photosynthesis
Chloroplasts also contain ribosomes. These ribosomes synthesise the proteins encoded by the chloroplast DNA
draw a diagram of a chloroplast
https://i0.wp.com/zhtutorials.com/wp-content/uploads/2023/10/Chloroplast.png?fit=674%2C401&ssl=1
chloroplast DNA
starch granule
state a key feature of plant cell
They are bounded by a cellulose cell wall
Function of cellulose cell wall
The cell wall provides strength to the plant cell
provide strength and rigidity to the plant cell
helps plant cell to maintain its shape
This is important because plant cells face a significant challenge due to water. Water is an essential reactant for photosynthesis and for other reactions taking place in the plant cell.
This means that water molecules have to enter and leave the plant cell.
If the water potential outside the plant cell is greater than inside. Then there will be a net inflow of water molecules by osmosis. This creates a large amount of hydrostatic pressure inside the plant cell pushing outwards.
So plant cell wall must be mechanically strong enough to resist this hydrostatic pressure
describe the structure and function of the cell walls found in plants, algae and fungI
