National 4 Biology Unit 1 Cell Biology Section

National 4 Biology Unit 1 – Cell Biology Section 2 – DNA, Genes and Chromosomes

We will be able to… • State that genes are located on chromosomes in the nucleus of every cell • State that a gene is a section of DNA which controls an inherited characteristic • State that genes are passed on from parents to offspring in the egg and the sperm • State that every individuals DNA is unique except for identical twins • State that DNA carries the instructions to make proteins and this is termed the genetic code • State that DNA is made up of building blocks made of sugar, phosphate and the four bases A, T, C and G • Give the complimentary base pair rule; A goes with T, C goes with G • Explain that by testing a DNA sample, this information can be used to identify a person’s father, or can be used to link people to a crime scene • State that testing for a particular gene can identify a genetic disorder • Discuss examples of inherited characteristics

Which of these Simpsons characters are related? How can you tell which characters are related even if you have never seen the Simpsons?

Inheritance • Characteristics like hair colour, eye colour, nose shape and many others are passed down from your parents. • This is called inheritance

How are Characteristics Inherited? The genetic information to make all of these characteristics is found in every cell in your body. It is hidden in the nucleus of each cell.

What makes Organisms Different? Organisms differ because they have different genes. l Humans have human genes l Gerbils have gerbil genes l Bananas have (yes, you’ve guessed it) banana genes! Nobody else in the whole world has the same DNA as you!

Genetic information The nucleus of living cells contain chromosomes which are made up of a sequence of genes.

Inside the Nucleus

Chromosome Strand Cytosine Adenine Strand Guanine Thymine

Your DNA • Your DNA is unique to you (unless you are an identical twin). • This is because sperm cells and egg cells are all genetically different, even from the same parents. • This is why you are not identical to your brother or sister.

Chromosomes • Humans have 46 chromosomes in each nucleus. • 23 of these came from the mother in the egg cell. • 23 came from the father in the sperm cell. • During fertilisation the 2 sets combined to give the full set of 46 chromosomes.

Identical twins • Identical twins have identical DNA. • This is because they came from the same fertilised egg which then split into two. • Non identical twins came from two eggs fertilised by two sperm, so they are genetically different.

How Twins are Formed

Structure of DNA Each molecule of DNA consists of 2 strands, where each strand is made up of repeating units called Nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. If you think of the double helix structure as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs.

Nucleotides Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). • Deoxyribose sugar • Phosphate • Organic Base

Chromosomes and their genes are made of a molecule called DNA stands for deoxyribonucleic acid. Each chromosome is a very long molecule of tightly coiled DNA. The DNA molecule looks like a twisted ladder this spiral shape is called a DOUBLE HELIX

DNA Bases The double helix ‘ladder’ of a DNA molecule is held together by ‘rungs’ made from pairs of chemicals called bases. A Adenine C Cytosine G Guanine T Thymine There are four types of bases, and they are usually identified by their initials.

Base pairs hold the two strands of the DNA helix together. C G A T It is the sequence of these bases along a DNA molecule that forms an organisms genetic code.

The ‘Rules’ Scientists discovered that in any sample of DNA: Number of A = number of T Number of C = number of G

DNA and Proteins The sequence of bases on a DNA molecule determines the sequence of amino acids in a protein A A T C T G C A T G G C A T C A G T

Coding for a Protein A different sequence of bases on a DNA molecule produces a different sequence of amino acids in a protein. A A T C T G C A T G G C A T C A G T

Proteins are large molecules made by joining small subunits called amino acids together. There are 21 different amino acids. Different proteins have different combinations of the amino acids.

Why do we need Proteins? • Enzymes are proteins that help us digest food. • Hair is protein. • Skin contains protein. • Antibodies which fight disease are proteins. • Our blood contains proteins. • Hormones – these are chemical messengers

DNA Profiling • Everyone’s DNA is unique. • It is because of this property that we are able to catch criminals using DNA samples. • DNA samples can also be used to identify the father of a child (paternity testing)

What Protein is Missing? The following people suffer from a condition because they cannot correctly code for a certain protein. Do you know what protein they might be missing? Simon is 11 years old. Suzy He was born with a condition called Albinism is 20 years old. She has suffered from a condition (Albino). called diabetes since she was 7 years old. The symptoms of diabetes are tiredness and extreme thirst. Simon’s body cannot make a protein that gives hair, skin and eyes their unique colour. he hasshe no can’t colourmake in his eyes, This Therefore condition means a hormone (protein) hair or skin. that removes the sugar from her blood after she eats. What protein is he missing? What is she missing? INSULIN Melanin

Genetic Code (T or F) 1. Your entire genome is found in every cell in your body (except the sperm and egg). True 2. A baby has exactly the same genes as his or her father and mother. False 3. Sperm and eggs have the same number of chromosomes as other cells; after they combine, the number is cut in half. False 4. Your genome is over 99% identical to every other human on earth. True 5. Genes are found on DNA, which makes up chromosomes in the nucleus of a cell. True 6. All living things on earth share certain identical sequences of bases on their genome. True 7. The more complex animals have more chromosomes and more DNA. False 8. The bases in DNA can be sequenced in an almost infinite number of ways to spell out the "sentence" of a living organism's genome. True 9. There is one base on each rung of the DNA "ladder. " False 10. Only animals have DNA in their cells. False

Questions • Where are genes located? • Where are chromosomes found? • What do genes contain the instructions for making? • Give 3 examples of proteins found in your body.

Summary Questions 1. What cell part controls the cells activities? Nucleus 2. What structures inside the nucleus contain genetic information? Chromosomes 3. How many chromosomes do humans have? 4. What are chromosomes made of? DNA 46

Can you make a DNA molecule? • Collect a DNA Origami sheet and instruction sheet. • Watch how to start then follow the instructions.

Research Activity Select a DNA scientist and research their work and life. Choose from the following list: • Francis Crick • James Watson • Rosalind Franklin • Maurice Wilkins

Now I can…. . • State that genes are located on chromosomes in the nucleus of every cell • State that a gene is a section of DNA which controls an inherited characteristic • State that genes are passed on from parents to offspring in the egg and the sperm • State that every individuals DNA is unique except for identical twins • State that DNA carries the instructions to make proteins and this is termed the genetic code • State that DNA is made up of building blocks made of sugar, phosphate and the four bases A, T, C and G • Give the complimentary base pair rule; A goes with T, C goes with G • Explain that by testing a DNA sample, this information can be used to identify a person’s father, or can be used to link people to a crime scene • State that testing for a particular gene can identify a genetic disorder • Discuss examples of inherited characteristics

Word Definition Cells Nucleus The building blocks of all living things Organelle in cells which controls the cell’s activities Gene Strand of DNA which codes for a protein Bases Parts of the DNA structure which pair up with one another Chromosomes Structures found in nucleus which carry genetic information DNA Amino Acids Mutation A molecule which carries the blueprint for life. Small chemical units which make up a protein and are coded for by triplets of DNA. This is caused by a mistake in the code on the gene and therefore a faulty protein. Hydrogen Bonds This type of pairing holds the two DNA strands together. Adenine A base found on DNA which is represented by the letter A. Thymine A base found on DNA which is represented by the letter T. Guanine A base found on DNA which is represented by the letter G. Cytosine A base found on DNA which is represented by the letter C