What is DNA?

O O=P-O Double stranded helix Antiparallel Made up of nucleotides N Nitrogenous base (A, G, C, or T) O O=P-O Phosphate Group CH2 C1 C4 C3 C2 5 Sugar (deoxyribose) Pentose O

DNA Double Helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

Recap DNA Replication DNA (helicase) unwinds to form 2 templates (RNA) primer is then bound to the starting DNA site. Begin of replication, an enzyme called DNA polymerase binds to the (RNA) primer, which indicates the starting point for the replication. Occurs at several locations on DNA strand DNA polymerase can only synthesize new DNA The DNA polymerase can only travel on one side of the original strand without any interruption (3’ to 5’). Since the DNA replication on the lagging strand is not continuous, the replicated DNA is fragmented with fragments added by the enzyme ligase. Semi-conservative replication!

Still not clear …..

Same but different .... Four of the many different types of human cells (a) Three muscle cells (partial) (b) A nerve cell (partial) They all share the same genome What makes them different? (c) Sperm cells (d) Blood cells

What things similar/different? 8

Why have specialised cells? Division of Labour Multicellular organisms have millions of cells To ensure all process carried out – division of labour where cells become differentiated and specialised to carry out 1 specific function

How many chromosomes/DNA? 10

Everything has the same DNA – so what happens to get Big Question Everything has the same DNA – so what happens to get Each and every cell? P12 The genotype of a cell is determined by the sequence of bases in its DNA. DNA is the molecule of inheritance and can direct its own replication. Structure of a DNA nucleotide (deoxyribose sugar, phosphate and base). Nucleotides bond to form a sugar–phosphate backbone. Base pairs (adenine, thymine and guanine, cytosine,) held by weak hydrogen bonds forming a double helix. Double stranded antiparallel structure with deoxyribose and phosphate at 3' and 5' ends of each strand.

Gene Expression; On and Off Once a cell becomes differentiated – the genes that code for only specific proteins to the workings of that cell are turned on. Only 3-5% of genes expressed in a typical human cell

Think! For a nerve cell neurotransmitters would be switched on, but mucus would be off What genes would be turned on for ... Goblet cell in lining of wind pipe Saliva cells White blood cells Ovary cells

Selective Gene Expression Once a cell becomes differentiated it only expresses the genes that produce the proteins characteristic for that type of cell. So what happens before .......

Review Genes are .... For different cells to become specialised ....