2.1.1 Structure of eukaryotic cells

What are the distinguishing features of eukaryotic cells?

• Cytoplasm containing membrane-bound organelles.

• DNA enclosed in a nucleus.

Which other cell types are similar to plant cells?

• Algal and fungal cells are similar to plant cells.

Describe the structure and function of the cell-surface membrane.

• Structure: phospholipids form a bilayer with hydrophobic fatty acid tails facing inwards and hydrophilic phosphate heads facing outwards.

• Function: selectively permeable to control substance passage, with molecules, receptors, or antigens on the surface allowing cell recognition and signalling.

What are the main structural features of the nucleus?

• Nuclear envelope with double membrane and nuclear pores.

• Nucleoplasm.

• Nucleolus.

• Histone-bound, linear DNA existing as chromatin (condensed) or chromosomes (highly condensed).

What are the functions of the nucleus?

• Holds genetic information in the form of DNA coding for amino acid sequences of polypeptides.

• Site of DNA replication

• Site of transcription, producing mRNA.

• Nucleolus makes ribosomes or rRNA.

Describe the structure and function of a ribosome.

• Structure: made of ribosomal RNA and protein with two subunits; not a membrane-bound organelle.

• Function: site of protein synthesis, specifically translation.

Describe the structure and functions of rough and smooth endoplasmic reticulum.

• Rough ER: ribosomes on surface synthesise proteins during translation; proteins are processed, folded, and transported inside rER, then packaged into vesicles for transport to the Golgi apparatus.

• Smooth ER: synthesises, processes, transports, and packages lipids and carbohydrates, for example cholesterol and steroid hormones.

Describe the structure and functions of the Golgi apparatus and Golgi vesicles.

• Golgi apparatus: flattened membrane sacs that modify proteins and lipids, package them into Golgi vesicles, and produce lysosomes.

• Golgi vesicles: small membrane sacs that transport proteins and lipids to their required destination, fusing with the cell-surface membrane.

Describe the structure and function of a lysosome.

• Structure: membrane-bound sac containing hydrolytic enzymes.

• Function: releases hydrolytic enzymes such as lysozymes to hydrolyse pathogens or worn-out cell components.

Describe the structure and function of mitochondria.

• Structure: outer membrane, cristae (inner membrane folds), and matrix containing small 70S ribosomes and circular DNA.

• Function: site of aerobic respiration, producing ATP to release energy for processes such as protein synthesis, vesicle movement, or active transport.

Describe the structure and function of chloroplasts.

• Structure: double membrane, stroma containing thylakoid membrane, small 70S ribosomes, circular DNA, and starch granules; grana are stacks of thylakoid; lamella are thylakoids linking grana.

• Function: pigments absorb light energy for photosynthesis to produce organic substances.

Describe the structure and function of the cell wall in plants, algae and fungi.

• Structure: composed mainly of cellulose in plants and algae; composed of chitin in fungi.

• Function: provides mechanical strength and prevents the cell changing shape or bursting under osmotic pressure.

Describe the structure and function of the plant cell vacuole.

• Structure: tonoplast membrane surrounding cell sap.

• Function: maintains turgor pressure to stop plant wilting and stores sugars, amino acids, pigments, and waste chemicals.

How are eukaryotic cells organised in complex multicellular organisms?

• Cells become specialised for specific functions.

• Tissue: group of specialised cells working together.

• Organ: aggregations of tissues performing specific functions.

• Organ system: group of organs working together.