DNA Noadswood Science, 2016

DNA To describe what DNA is and what it’s purpose is Tuesday, August 07, 2018 DNA To describe what DNA is and what it’s purpose is

Precise Learning The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes In body cells the chromosomes are normally found in pairs.   Students should be able to describe the structure of DNA and define genome. The genetic material in the nucleus of a cell is composed of a chemical called DNA. DNA is a polymer made up of two strands forming a double helix. The DNA is contained in structures called chromosomes. A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.

Inherited Children usually look a little like their father, and a little like their mother, but they will not be identical to either of their parents Why is this? Offspring get half of their inherited features from each parent During fertilisation, the nucleus from the sperm cell joins with the nucleus in the egg cell, and a new nucleus is formed with all the genetic information needed…

Genetic Information nucleus The genetic information passed from parent to offspring is contained in genes, carried by chromosomes in the nucleus All body cells have a nucleus which contains all genetic information nucleus

Genetic Information In a fertilised egg there are 23 pairs of chromosomes (23 unpaired chromosomes from your mother and 23 unpaired chromosomes from your father)

Chromosomes & Genes A gene is a section of DNA that carries the code for a particular protein Different genes control the development of different characteristics of an organism – many genes are needed to carry all the genetic information for a whole organism Chromosomes, found in the cell nucleus, contain many genes

DNA DNA is a polymer – two strands coiled together in the shape of a double helix

Genes and Proteins A gene is a small section of DNA found on a chromosome – each gene codes for a particular sequence of amino acids which are put together forming a specific protein Only 20 amino acids are used, but they make thousands of proteins (based on the amino acid order)

Species The number of chromosomes and genes varies from species to species For example, cells in human beings have 46 chromosomes (23 pairs) that carry about 30,000 genes in each cell; and cells in fruit flies have eight chromosomes that carry about 13,600 genes

DNA Genes are made up of short lengths of DNA (deoxyribose nucleic acid) In the 1950’s Watson and Crick were the first to come up with the structure of DNA

DNA

Each chromosome is a very long molecule of tightly coiled DNA Chromosomes and their genes are made of a molecule called DNA DNA molecules carry the code that controls what your cells are made of and what they do Each chromosome is a very long molecule of tightly coiled DNA

DNA Investigation Complete the DNA extraction experiment: - Dissolve 3g of salt into 100cm3 of water in a 250cm3 beaker. Add 10cm3 of washing up liquid, and stir gently until it dissolves Mash your fruit pieces using the pestle and mortar – when it is as mashed as possible put it into another 250cm3 beaker and add an equal volume of the solution made in the previous step to it – stir the mixture Place the beaker inside a larger beaker of hot water, and leave for 15 minutes Pour the mixture through a filter funnel with filter paper inside – collect the juice in a small beaker. Tilting the beaker slightly pour ice-cold ethanol down the side very slowly – stop when you have added as much ethanol as you have juice

DNA Structure

Lobed (left) & lobeless (right) ears Inherited Some variations are inherited, whilst other variations are due to environmental factors Inherited variation is a characteristic you have got from your parents - what can you inherit? Gender Eye colour Hair colour Skin colour Lobed or lobeless ears Lobed (left) & lobeless (right) ears

Summary

Practice Questions Where in a cell is DNA found? What are chromosomes made up of? Explain why DNA molecules are described as a double helix

Answers Where in a cell is DNA found – in the nuclues What are chromosomes made up of – long molecules of coiled up DNA Explain why DNA molecules are described as a double helix – they are made up of two strands coiled together in a double helix shape