Year 10 Human Biology Unit 1.2 Making new cells Year 10 Human Biology Unit 1.2

Why are cells important? Cells are the building block of organisms. Your life began as a single cell and over time that single cell has increased in number to create an organism that is now billions of cells. Each cell (except RBC) contains a nucleus and an exact copy of your DNA.

What role does DNA have? DNA contains the genetic code It is used to build proteins that are needed by the cells and develop characteristics seen at the organism level. Each time a cell divides to create two new cells, the DNA is copied so there is no loss to our genetic material.

How does this occur? The process of copying DNA is called REPLICATION. There are a number of steps involved to ensure that the new cells produced are genetically identical There are enzymes involved in this process as well

The steps… 1 – The DNA molecule unwinds and unzips, exposing the nitrogen base code

Next…? 2 – Free nucleotides pair up to the exposed bases following the complimentary base pair rule.

And then? 3 – The sugar phosphate molecules bond with neighbouring nucleotides and 2 strands of DNA are formed.

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Why is this important? Cell division is important for Growth and repair of the human body Creating gametes (sex cells) for reproduction DNA is important as it controls ALL activities of the cells.

Cell division Cell division for growth and repair is called MITOSIS The end result of mitosis is TWO Diploid daughter cells Genetically identical

MITOSIS DNA replication Chromosomes become visible, nuclear membrane disappears Chromosomes line up at the equator Chromatids are pulled to opposite poles The cell divides into 2 and the nuclear membrane reforms

Diploid vs Haploid? Diploid: the full compliment of DNA for a cell. Haploid: half the compliment of DNA for a cell. Therefore the diploid number for a human is 46 and the haploid is?? Why is this significant?

Making sex cells Cell division is also important in the production of gametes (sex cells) At fertilisation a sperm will unite with an ovum to create a zygote. If both the sperm and the ovum were diploid, how many chromosomes would the zygote end up with?

Fixing the problem 92 chromosomes is too much…! So the process of cell division to REDUCE chromosome number is called MEIOSIS End result of meiosis FOUR daughter HAPLOID cells Not genetically identical

MEIOSIS 1 - DNA replicates 2 – Chromosomes appear and the nuclear membrane disappears 3 – Chromosome PAIRS are pulled to opposite ends of the cell and the cell splits 4 – In Meiosis 2 the chromatids now separate and are pulled to opposite ends of the cells 5 - The 2 cells split again to form 4 haploid cells

Chromosome Terminology! Draw the following below and label the following: sister chromatids, centromere, gene. An unreplicated chromosome A replicated chromosome An unreplicated pair of homologous chromosomes A replicated pair of homologous chromosomes

Cell division in reproduction Asexual reproduction Sexual reproduction Offspring are genetically identical to their one parent This is achieved through mitosis Many plants and animals are able to reproduce asexually. Offspring are a mix of two parents This is achieved through meiosis and the formation of gametes The chromatids in each gamete are not exact copies of the parents chromosomes.