Cell organelles

Question 1

describe what can happen if a protein has folded

Answer 1

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

Question 2

role of nucleus

Answer 2

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

Question 3

where does translation take place

Answer 3

Translation takes place on a ribosome

Question 4

state different destinations of proteins

different proteins have different destinations

Answer 4

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

Question 5

Which organelles is involved int eh targeting of different proteins to different destinations

Answer 5

how proteins are targeted to different destinations is complex. A LOT OF THIS TARGETTING INVOLVES THE ROUGH ENDOPLASMIC RETICULUM and the Golgi apparatus

Question 6

what do ribosomes consist of, and what are they called]

draw the structure of a ribosome

Answer 6

Ribosomes consist of two subunits - large sub unit and small subunit

https://www.medschoolcoach.com/wp-content/uploads/2022/12/RibosomeStructureFunction-Figure1.jpg

Question 7

What does each subunit include

Answer 7

Each subunit contains a number of different proteins plus ribosomal RNA

Question 8

IN cells, where are a large number of ribosomes found

Answer 8

In any cell, a large number of ribosomes are found in the cytoplasm

Question 9

State the function of ribosomes found in the cytoplasm

Answer 9

Ribosomes found in the cytoplasm translate proteins which remain the cytoplasm

Question 10

If not found in the cytoplasm, where are other ribosomes found

Answer 10

Other ribosomes are found attached to the rough endoplasmic reticulum

Question 11

Describe the structure of the Rough ER

Answer 11

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

Question 12

Describe how a protein is transferred from the rough ER to the Golgi apparatus to out of the cell

Answer 12

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

Question 13

What feature will be present on cells which secrete large amounts of protein

Answer 13

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

Question 14

Describe the role of the RER

Answer 14

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

Question 15

Describe the structure/role of the SER

Answer 15

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

Question 16

Describe the role/structure of the Golgi Apparatus

Answer 16

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

Question 17

Describe the structure of lysosomes

Answer 17

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

Question 18

Describe the function of lysosomes

Answer 18

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

Question 19

where is mitochondria found

Answer 19

Mitochondria is found in all eukaryotic organisms including animals, plants and fungi

Question 20

stages of aerobic respiration

Answer 20

Glycolysis - occurs in cytoplasm

The Krebs Cycle
Oxidative Phosphorylation (stage in aerobic respiration which requires oxygen)
– Both occur in mitochondria

Question 21

function of mitochondria

Answer 21

Mitochondria play a critical role in aerobic respiration to produce the energy carrying molecule ATP

Question 22

describe what happens in aerobic respiration

Answer 22

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

Question 23

describe the structure and function of mitochondria

Answer 23

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

Question 24

where do we usually find larger numbers of mitochondria

Answer 24

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

Question 25

Draw a mitochondria

Answer 25

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

Question 26

function of chloroplasts

Answer 26

the organelles where photosynthesis takes place

sites of photosynthesis

Question 27

where do we find chloroplasts and where are they not found within the plant (give an example)

Answer 27

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

Question 28

describe what happens in photosynthesis

Answer 28

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

Question 29

how many reactions does photosynthesis consist of

describe these reactions

Answer 29

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

Question 30

Describe the structure and function of chloroplasts

link the structures to their functions

Answer 30

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

Question 31

draw a diagram of a chloroplast

Answer 31

https://i0.wp.com/zhtutorials.com/wp-content/uploads/2023/10/Chloroplast.png?fit=674%2C401&ssl=1

chloroplast DNA
starch granule

Question 32

state a key feature of plant cell

Answer 32

They are bounded by a cellulose cell wall

Question 33

Function of cellulose cell wall

Answer 33

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

Question 34

describe the structure and function of the cell walls found in plants, algae and fungI