GCSE Biology B (Combined) OCR

Cells and Genetic Material

Cells and Genetic Material

What are Cells?

• Every living organism is composed of basic building blocks known as cells.
• Cells contain different sub-units, or organelles, each with defined roles.
• In humans, body cells contain a nucleus which houses the chromosomes.
• Different types of cells include prokaryotic cells (like bacteria) and eukaryotic cells (in complex organisms like plants and animals).

Genetic Material in Cells

• The genetic material of a cell is stored within the nucleus in complex structures known as chromosomes.
• Chromosomes are composed of a long strand of DNA (deoxyribonucleic acid), coiled up tightly.
• DNA is made up of two stands twisted around each other to form a double helix.
• Sections of the DNA that code for particular traits are known as genes.

Genes and Variation

• Genes determine the characteristics that an organism has, like eye colour or blood type.
• Genes come in different versions known as alleles.
• Organisms inherit two copies of each gene, one from each parent.
• Different combinations of genes result in genetic variation.

DNA Structure

• DNA is made up of a sequence of nucleotides each composed of a sugar, phosphate and base.
• The order of these bases determines the information available for building and maintaining the organism.
• There are four types of bases in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G).
• Adenine always pairs with thymine (A-T), and cytosine always pairs with guanine (C-G), forming the base pairs.

DNA Replication

• DNA can make copies of itself in a process known as DNA replication.
• During replication, the DNA unwinds and the double helix separates into two individual strands.
• Each strand then acts as a template on which a new complementary strand is assembled.
• This ensures that every new cell has a complete set of identical DNA.

Genetic Code and Protein Synthesis

• The order of the bases in a gene forms the genetic code.
• This code provides the instructions for the production of specific proteins in a process called protein synthesis.
• Protein synthesis involves two key stages: transcription and translation.
• During transcription, a copy of the gene's code is made using a molecule called messenger RNA (mRNA).
• During translation, the mRNA is used as a template to assemble the protein.

This overview should help in the understanding of basic cell structure and the role and importance of genetic material within those cells. Remember, this knowledge forms the foundation for understanding more complex genetic processes.