1. DNA and the Genome Key Area 1 The Structure of DNA

2. Learning Intentions By the end of this topic you should be able to:  Name the molecules in a DNA nucleotide and identify them in a diagram  Name the type of bond on the backbone of the DNA molecule  Give the names of the 4 DNA bases  Describe the base pairing rule for DNA bases  Describe the role of hydrogen bonds in the DNA structure  State the name of the coiled structure adopted by DNA

3.  Identify the positions of 3’ and 5’ carbons on a DNA nucleotide  Identify the positions of 3’ and 5’ ends on a DNA strand  Describe how 2 strands of DNA align themselves to each other Learning Intentions

4. You should already know that: DNA is inherited. DNA is the genetic material of living things. DNA is located within the nucleus of all cells apart from red blood cells. DNA is a long chemical sequence and this sequence contains the information needed for that living thing to develop, survive and pass its genetic information on to the next generation. The DNA chemical sequence differs between individuals. The pattern of this sequence is called the genotype.

5. What is DNA? DNA = Deoxyribonucleic acid DNA is the storage molecule found in ALL living cells whose sequence of bases determines the organisms genotype and the structure of its proteins. Chromosomes are made of DNA and are INHERITED Image source: http://ipkitten.blogspot.com

6. Structure of DNA A molecule of DNA has two strands of repeating units called nucleotides. 5’ end 3’ end deoxyribose sugar phosphate nitroegeous base 5’ pronounced “5 prime”

7. Carbon 1 Carbon 2 Carbon 3 Carbon 4 Carbon 5

8. Note the numbering of the carbons C1 has the base attached, C5 the phosphate

9. Structure of DNA DNA has four different types of nucleotides each with a different base (attached to C1). Thymine Adenine Cytosine Guanine

10. Base Pairs Each base can only join with one other type of base. Weak hydrogen bonds join each base to its complementary partner. Adenine (A) only pairs with Thymine (T) Guanine (G) only pairs with Cytosine (C)

11. A = adenineT =thymine G = guanineC = cytosine Strong chemical bond Weak hydrogen bonds A G T C Note that there are 2 hydrogen bonds between the bases A-T and 3 hydrogen bonds between G- C. This means more energy is required to break the G-C bonds in DNA than the A-T

12. Structure of DNA DNA molecules are made of two strands wound together like a spiral ladder, this is called the DOUBLE HELIX. The uprights are formed by ‘sugar- phosphate backbones’ and bases pair forming the rungs

13. DNA Strand DNA Nucleotide 5 Carbon Sugar (deoxyribose) Phosphate Group Base strong chemical bond Strong chemical covalent bonds (PHOSPHODIESTER BONDS) form between the phosphate group of one nucleotide (5C) and the sugar (3C) of another to form a permanent strand…(sugar-phosphate backbone)

14. The enzyme which links nucleotides in a chain is known as DNA Polymerase Phosphat e Organic Base Deoxyribose Sugar Strong chemical bond OH P O O O CH2 O H or OH O H H H N N 1 2 3 4 5 6 3 5 P O O O O CH2 O H or OH OH H H H N N 1 2 3 4 5 6 3 5 - 5’ 3’

15. A NUCLEOTIDE CHAIN The result of the joining of the nucleotides is the SUGAR PHOSPHATE BACKBONE with the bases attached

16. DNA is double stranded with the two strands running in opposite directions. This is known as an antiparallel arrangement. 5’ 3’ 5’

17. Identifying What The Genetic Material Was In the early 20 th century it was not known whether the genetic material responsible for inherited characteristics was DNA or protein Over the following years a series of experiments were carried out by various scientists to definitively show which of the 2 was the hereditary material The following slides and PowerPoints follow these scientists and their experiments in showing DNA and not protein is the inherited material

18. TRANSFORMING PRINCIPAL In 1928, Fredrick Griffith used 2 strains (S & R) of a bacterium called Streptococcus pneumonia – one of which caused pneumonia (S) and one which was harmless (R) – to show that some component had passed from one strain to the other. The cells had been said to be transformed. A second scientist named Avery proved this ‘transforming component’ was DNA and not protein and this was backed with evidence a few years later from Hershey and Chase who used bacteriophages (see later)

19. Griffith Experiment Some component from dead S cells has passed to live R cells

20. More details on these experiments can be found on the PowerPoints in the Extra PowerPoints folder

21. 1.What are the 3 components of a DNA nucleotide?

22. 2.Which carbons are the phosphate and base attached to?

23. 1.What are the 3 components of a DNA nucleotide? 2.Which carbons are the phosphate and base attached to? 3.What are the names of the 4 bases, how do they pair and what hold them together?

24. 1.What are the 3 components of a DNA nucleotide? 2.Which carbons are the phosphate and base attached to? 3.What are the names of the 4 bases, how do they pair and what hold them together? 4.Describe the structure of a DNA molecule

25. 1.What are the 3 components of a DNA nucleotide? 2.Which carbons are the phosphate and base attached to? 3.What are the names of the 4 bases, how do they pair and what hold them together? 4.Describe the structure of a DNA molecule 5.Which type of bond connects one nucleotide to the next, which carbons are involved and which enzyme catalyses this reaction?

26. 1.What are the 3 components of a DNA nucleotide? 2.Which carbons are the phosphate and base attached to? 3.What are the names of the 4 bases, how do they pair and what hold them together? 4.Describe the structure of a DNA molecule 5.Which type of bond connects one nucleotide to the next, which carbons are involved and which enzyme catalyses this reaction? A1 Phosphate, Deoxyribose sugar, Base A2 Phosphate – C5, Base – C1 A3 Adenine – Thymine, Cytosine – Guanine, Weak hydrogen bond A4 Double stranded helix A5 Phosphodiester bond, C3 – C5, DNA Polymerase

27. Organisation of DNA in Prokaryotic & Eukaryotic Cells

28. Learning Intentions By the end of this topic you should be able to: Identify prokaryotes and eukaryote cells from diagrams Describe the key similarities and differences between prokaryote and eukaryote cells Describe structure of a plasmid and can name the types of cells where they are found Describe structure of circular chromosomes and identify the location and types of cells where they are found Compare the DNA found in mitochondria and nucleus of eukaryote cells Describe the DNA in linear chromosomes found in nucleus of eukaryote cells

29. You should already know: DNA is the genetic material of living things DNA structure. Difference between a prokaryote and eukaryote.

30. Cell Size Remember 1m = 1000mm 1mm (10 -3 m ) = 1000µm 1µm (10 -6 m)= 1000nm 1nm (10 -9 m) = 1000pm

31. There are two main classifications of cells 1)Prokaryotic – bacteria 2)Eukaryotic – fungi, green plants and animal cells

32. Prokaryotic Cell Structure (Bacteria)

33. Prokaryotic DNA Prokaryotic DNA is different to eukaryotic DNA in that it is LINEAR (although sometimes forms a circle) and is associated with few (or no) proteins. It is not located in a nucleus but is instead found in a nucleoid region **Remember – bacterial cells also have extra genetic material in the form of PLASMIDS

34. Nucleoid – This is highly condensed DNA in the form of a single circular molecule. It is not enclosed in a membrane Cytosol – This is the watery gel making up the majority of the cell content and is the site of bacterial metabolism Ribosomes – Bacteria have many ribosomes suspended in the cytosol or attached to plasma membrane, essential due to bacterias high proliferation rate

35. Cell wall – Tough outer coat made of peptidoglycan Capsule – The bacterial has a mucilaginous coating known as the capsule which protects the cell and helps it adhere to other cells or surfaces Pili – appendage used to attach to surfaces, can be up to several hundred per cell Flagellum – allows the cell to move

36. Eukaryotic Cells May be unicellular or multicellular DNA is enclosed in a double nuclear membrane They contain numerous membrane-bound organelles They can be divided into fungi, animal or plant cells

37. Structure of a typical Eukaryotic animal cell

38. Nucleus This has a double membrane known as the nuclear envelope which encloses the liquid nucleoplasm. Arranged in the nucleoplasm is the chromatin made up of DNA and associated histone proteins. Within the nucleus is also found the nucleous, a spherical body where rRNA is transcribed The nucleus contain pores to allow large molecules pass to and from the cytoplasm

39. Endoplasmic reticulum - this is a series of membranes continuous with the nuclear membrane. The smooth ER (no ribosomes attached) synthesises lipids, metabolises carbs and detoxifies drugs/poisons The rough ER (ribosomes attached) folds and modifies proteins made on the ribosomes before going to the Golgi apparatus Golgi apparatus – This further modifies, stores and secretes proteins.

40. Mitochondrion – membrane bound organelle, site of aerobic respiration. Outer membrane is smooth, inner membrane has cristae folds. Mitochondria also contains small circles of DNA Plasma Membrane – controls entry and exit of materials via diffusion, osmosis and active transport. Ribosome – composed of two subunits which come together in the presence of mRNA for protein synthesis

41. Plant Cell

42. Like other eukaryotes, the plant cell is enclosed by a plasma membrane, which forms a selective barrier allowing nutrients to enter and waste products to leave. Unlike other eukaryotes, however, plant cells have retained a significant feature of their prokaryote ancestry, a rigid cell wall composed of cellulose. Chloroplasts convert light to chemical energy A single large vacuole acts as a water reservoir

43. Chloroplasts Like mitochondria, chloroplasts have a double membrane, but in addition chloroplasts have a third membrane called the thylakoid membrane. This is folded into thin vesicles enclosing small spaces called the thylakoid lumen. The thylakoid vesicles are often layered in stacks called grana..Chloroplasts also contain DNA and ribosomes and often store the products of photosynthesis as starch grains and lipid droplets.

44. Differences Between Prokaryote and Eukaryote Cells FeatureProkaryote (bacteria)Eukaryote (fungi, plant, animal) Size small, mean diameter 0.5 - 5  m Up to 40  m common Genetic material Circular DNA in cytoplasm DNA associated with proteins to form a chromosome, found within a nucleus Organelles Few present (mainly ribosomes) and none surrounded by a plasma membrane Many organelles; Some with double membranes e.g. nucleus, mitochondria and chloroplasts. Many with a single membrane e.g. golgi apparatus and endoplasmic reticulum Cell Walls Rigid formed from glycoproteins (mainly murein) Animal: none Fungi: Rigid, formed from chitin Plants: Rigid, formed from cellulose

45. 0.2-2 µm 4 cm Too small to show the real size, but you could fit 10,000 along the length of a fingernail! The length of DNA in one chromosome into this... The packaging of DNA in eukaryotic chromosomes

46. Stages of mitosis The organisation of DNA in a eukaryotic cell depends on the stage of mitosis they are in. Think back to National 5…what happens during cell division…

47. The stages of the mitosis have different names.

48. DNA is thousands of times longer than the cell it is going into so it must be arranged in such a way that it fits into the nucleus. To do this, the DNA is tightly coiled around a series of proteins called HISTONES Every 8 of these histones further coil together to make NUCLEOSOMES The nucleosomes then pack together to make CHROMATIN fibres which loop along a protein scaffold Eventually you have a tightly coiled and folded chromosome structure

49. Nucleosomes DNA double helix is wrapped around histone proteins forming nucleosomes (beads on a string)

50. The pieces of DNA between the nucleosomes is known as linker DNA and is a constant length. The combination of DNA and protein is called chromatin. This level of organisation is seen through out the cell cycle and mitosis.

51. Thick chromatin fibre The chain of nucleosomes then folds into a thicker chromatin fibre. Seen during interphase.

52. Looped fibres The thick chromatin fibre then folds again, on a non-histone protein scaffold, to form looped fibres. Seen in prophase.

53. More folds to make chromosome The folded chromatin then folds further. To produce a condensed chromosome – seen in metaphase.

55. 1. If a cell is 200nm long, how big is this in µm and mm?

56. 2.Give 2 ways in which a bacterial cells DNA differs from a eukaryotes

57. 1.If a cell is 200nm long, how big is this in µm and mm? 2.Give 2 ways in which a bacterial cells DNA differs from a eukaryotes 3.What is the function of a bacterial cells flagellum?

58. 1.If a cell is 200nm long, how big is this in µm and mm? 2.Give 2 ways in which a bacterial cells DNA differs from a eukaryotes 3.What is the function of a bacterial cells flagellum? 4.Name 3 double membrane and 2 single membrane structures found in eukaryote cells

59. 1.If a cell is 200nm long, how big is this in µm and mm? 2.Give 2 ways in which a bacterial cells DNA differs from a eukaryotes 3.What is the function of a bacterial cells flagellum? 4.Name 3 double membrane and 2 single membrane structures found in eukaryote cells 5.DNA can be wound around proteins. Name these proteins and name the structure these form when 8 wind together

60. 1.If a cell is 200nm long, how big is this in µm and mm? 2.Give 2 ways in which a bacterial cells DNA differs from a eukaryotes 3.What is the function of a bacterial cells flagellum? 4.Name 3 double membrane and 2 single membrane structures found in eukaryote cells 5.DNA can be wound around proteins. Name these proteins and name the structure these form when 8 wind together A1 0.2µm 0.0002mm A2 Linear and not within a nucleus (within nucleoid region) A3 Movement of bacterial cell A4 Double membranes – nucleus, mitochondria, chloroplast Single – ER, Golgi A5 Histones, Nucleosomes