A-LEVEL B2.1.1 CELL STRUCTURE

What is the structure of mitochondria?

Structure: Usually oval-shaped, bound by a double membrane (inner + outer) called the envelope. The inner membrane is folded to form projections called cristae. It has a fluid within called the matrix which contains the enzymes needed for respiration. Contains its own DNA (called mitochondrial DNA) + ribosomes.

What is the function of mitochondria?

It is the site of the final stages of respiration and produces ATP.

What is the structure of the nucleus?

It is surrounded by a semipermeable double membrane called the nuclear envelope which contains small holes called nuclear pores, which allows molecules to enter and leave the nucleus (e.g. mRNA leaving the nucleus to the cytoplasm in protein synthesis. Contains a nucleolus made up of RNA and proteins which is the site of ribosome production. Contains chromatin which is DNA wrapped around histone proteins, found in the nucleus, which condenses into chromosomes during cell division.

What is the function of the nucleus?

Stores DNA away from the cytoplasm for protection with the double membrane, the nuclear envelope, around it. Produces mRNA via transcription. Transports mRNA through nuclear pores to the cytoplasm where its translated into protein. Synthesis of ribosomes as the nucleolus makes ribosomal DNA. Controlling the cells activities.

Whats the structure of endoplasmic reticulum?

Network of membrane “sacs” called cisternae connected to the outer membrane of the nucelus. Can be rough (containing ribosomes) or smooth (no ribosomes)

Whats the structure of sER?

System of membrane bound sacs without ribosomes

Whats the function of sER?

Produces + processes non-protein molecules (e.g. lipids, carbohydrates etc.) OR Synthesis, storage + transport of lipids + carbohydrates

What is the structure of rER?

Structure: A network of membranes forming flattened sacs called cisternae. The surface of the cisternae is covered with ribosomes

What is the function of rER?

Function: The rER synthesises + transports proteins ; it also folds + processes proteins made by ribosomes on its surface

What is the structure of the golgi apparatus?

A series of fluid filled, flattened, curved, membrane bound sacs known as cisternae. Doesnt contain ribosomes. Contain smaller vesicles surrounding the edges.

What is the function of golgi apparatus?

Process + package lipids + proteins which is carried out by the cisternae. Store + transport lipids + proteins which is carried out by vesicles. Synthesise lysosomes which is carried out by specialised vesicles.

Explain the process of the journey of a protein from DNA in the nucleus to secretion from the cell.

1. DNA in the nucleus codes for proteins + is transcribed to form mRNA 2. mRNA is translated into protein by ribosomes on the surface of rER. 3. They then pass into its cisternae, where they are packaged into transport vesicles. 4. Vesicles are transported via the cells cytoskeleton to the golgi apparatus. 5. Vesicles fuse with the cis face of the golgi body. Proteins undergo modification. This is the process of folding the protein + attaching carbohydrate / lipid molecules to them. The proteins are then packaged into vesicles that exit the golgi body via its trans face. 6. Secretary vesicles fuse with the cell surface membrane + the protein is released by exocytosis. 

What is the structure of ribosomes?

They can be free-floating in the cytoplasm or attached to the ER, forming rER and are not surrounded by a membrane. It is formed of protein and RNA molecules made in the nucleolus of the cell. Composed of two subunits, a large subunit which joins amino acids and a small subunit with mRNA binding site.

What is the function of ribosomes?

Site of protein synthesis.

What is the structure of lysosomes?

Specialised forms of vesicles that contain hydrolytic enzymes (enzymes that break biological molecules). They are formed by the golgi body. It is bound by a single membrane.

What is the function of lysosomes?

They play an important role in the immune system as they can break down pathogens ingested by phagocytic cells. Used in apoptosis which is programmed cell death. Break down waste material such as worn-out organelles.

What is the structure of chloroplasts?

Surrounded by a double membrane. Contains a fluid called the stroma which is where some parts of photosynthesis occur. Have an internal network of membranes which form flattened sacs called thylakoids, which contain chlorophyll, which is also where light dependant reactions occur during photosynthesis. Several thylakoid stacks stacked together are called granum. Grana are linked together by lamellae. The starch produced by photosynthesis is present starch grains. Also contain ribosomes and DNA so can make their own proteins.

What is the function of the chloroplasts?

Site of photosynthesis.

What is the structure of plasma membrane/cell surface membrane?

Formed by a phospholipid which is the bilayer of phospholipids spanning a diameter of around 10nm. It is made up of mainly lipids and proteins.

What is the function of plasma membrane/cell surface membrane?

Controls the exchange of materials between in and out of the cell - so its described as partially permeable. It also has receptor molecules on it so it can respond to chemicals like hormones and detect signals from other cells.

What is the structure of the centrioles?