Biology

1. Biology DNA Structure And Replication

2. The Components and Structure of DNA • DNA – deoxyribonucleic acid • Deoxyribose – simple sugar in DNA • DNA is made up of nucleotides • Nucleotide – made of simple sugar, phosphate and a nitrogen base • 4 Nitrogen Bases in DNA • Adenine • Guanine • Cytosine • Thymine purines – double ring pyrimidines – single ring

4. Nucleotides join together to form long chains • Phosphate and deoxyribose form the backbone of the chain (sides of the ladder) • Nitrogen bases are the steps of the ladder • The amount of adenine equals thymine • The amount of guanine equals cytosine

6. phosphate deoxyribose hydrogen bond nitrogen base nucleotide

7. History of DNA • Rosalind Franklin and Maurice Wilkins worked on the structure of DNA based on x-ray crystallography (pictures of DNA by x-rays). • James Watson and Francis Crick were also working on the structure of DNA • These scientists were trying to be the first to discover and prove the structure of DNA because they knew it would be one of the most important discoveries in the 20th century.

9. 1953 Watson and Crick proposed that DNA is made of two chains of nucleotides joined together by nitrogen bases • Two bases are held together by hydrogen bond • Two strands are complementary • Complementary base pairing • A and T • C and G • DNA is shaped in a double helix

11. A-A-G-C-T-T-G-C-C-A-T-C-A-G-T-G-G-A-C T-T-C-G-A-A-C-G-G-T-A-G-T-C-A-C-C-T-G

12. The Importance of Nucleotide Sequences • All living organisms are composed of A, T, C, G • How can organisms be so different from each other if their genetic material is made of the same four nucleotides? • Differences in organisms are from the sequence of the four different nucleotides and how many nucleotides • The closer the relationship between two organisms the greater the similarity in their order of DNA nucleotides • Scientists use nucleotide sequences to • Determine evolutionary relationships among organisms • Determine whether two people are related • Determine if DNA from a crime scene matches the DNA of a suspected criminal

13. Replication of DNA • Before a cell can divide by mitosis or meiosis it must first make a copy of its chromosomes • DNA Replication – DNA is copied • All organisms undergo replication

14. How DNA Replicates • During replication each strand serves as a pattern to make a new DNA molecule • The end result is the formation of two DNA molecules that are identical (duplicated chromosome)

15. Steps of Replication • Enzyme, DNA helicase, breaks the hydrogen bonds between nucleotides, this “unzips” the DNA molecule • Free nucleotides in the nucleus bond to the single strands. Enzyme, DNA polymerase glues the new strands together • This continues until the entire molecule has been unzipped and replicated • Each new strand formed is a complement of one of the originals or parent strand. • Two DNA molecules that are identical • Proofreading enzymes check the strand for mistakes and repair enzymes fix any mistakes that occur

18. From DNA to Proteins • Occurs in two steps – Transcription and Translation • Genes and Proteins • Proteins are key cell structures and regulators of cell functions • The sequence of nucleotides makes amino acids • Sequence of amino acids make proteins

19. RNA • RNA – ribonucleic acid • Differences Between DNA and RNA

20. DNA – A-C-G-T-G-A-A-G-C-T-G-T-A-C-A-G-T-C RNA – U-G-C-A-C-U-U-C-G-A-C-A-U-G-U-C-A-G

21. 3 Types of RNA that help to build proteins • Messenger RNA (mRNA) – takes information from the DNA in the nucleus to the ribosome • Ribosomal RNA (rRNA) – what ribosomes are made of • Transfer RNA (tRNA) – transports amino acids to the ribosome

22. Transcription • Transcription – make an RNA copy of a portion of a DNA strand • The process of transcription is similar to replication except • Transcription makes a single strand of RNA • Does not transcribe the entire strand of DNA

23. Steps of Transcription From DNA to RNA • An enzyme, RNA polymerase, unzips the molecule of DNA • As the DNA molecule unzips, RNA polymerase adds on RNA nucleotides to one strand of DNA. • Transcription continues until RNA polymerase reaches a special stop sequence - AAAAAAAA • mRNA molecule breaks away and leaves the nucleus

26. The Genetic Code • Proteins are built from amino acids • 20 different amino acids • Codon – each set of 3 nitrogen bases represents an amino acid • The order of nitrogen bases in DNA can determine the type and order of amino acids in a protein

27. 64 different combinations • 61 code for amino acids • 3 signal to stop protein synthesis • More than 1 codon can code for the same amino acid • Start codon is AUG (methionine) • Stop codons are UAA, UAG, UGA

29. Translation • From mRNA to Protein • Translation – the process of converting mRNA into a sequence of amino acids • Takes place at the ribosome

30. tRNA • Transfers amino acids to ribosome • One end of molecule carries amino acid • Other end carries anti-codon which complements the codon • Ex: mRNA – A-C-A • tRNA – U-G-U

31. Translating the mRNA Code • Steps of Translation • The first codon of the mRNA strand attaches to a ribosome • tRNA molecules carrying a specific amino acid approach the ribosome • tRNA anticodon pairs with mRNA codon • The first codon on mRNA is AUG which codes for amino acid methionine. AUG is the start codon for protein synthesis • A new tRNA molecule carrying an amino acid will pair with the next mRNA codon • As the process continues a chain of amino acids is made until it reaches a stop codon on the mRNA; UAA, UAG, UGA MOVIE

33. DNA T–A–C–A–G–G–T–C–G–T–T–A–C–G–G–A–C–T A–U–G–U–C–C–A–G–C–A–A–U–G–C–C–U–G–A mRNA U–A–C–A–G–G–U–C–G–U–U–A–C–G–G–A–C–U tRNA Amino Acids Meth. Serine SerineAspar. Alanine Stop

35. Mutations • Mutation: A Change in DNA • Mutation – any change in the DNA sequence • Mutations in Reproductive Cells • Mutation in egg or sperm can be passed on to offspring • Sometimes the mutation is so severe that the embryo does not survive • In rare cases a gene mutation may have positive effects

36. Mutations in Body Cells • This mutation would not be passed on to offspring • But the mutations can cause harm to the individual

37. DNA Mutations • Point Mutation • A change in a single base pair in DNA • A change in a single letter can change the amino acid, thus changing the protein made • 2. Frameshift Mutation • A single base is added or deleted from DNA • Can cause nearly every amino acid in the protein to be changed.

40. Chromosomal Mutations • Chromosomal Mutations – changes in the structure of chromosomes • They occur in all living organisms, but they are especially common in plants • Chromosomal mutations are rarely passed on to the next generation because: • The zygote usually dies • The mature organism is usually sterile

41. 4 Types of Chromosomal Mutations Deletion – a fragment of a chromosome breaks off, it can be lost

42. 2. Duplication – achromosome fragment attaches to its homologous chromosome, which will then carry two copies of a gene

44. 3. Inversion – fragment reattaches to the original chromosome in the reverse orientation

45. 4. Translocation – a fragment may join a nonhomologous chromosome

47. Causes of Mutations • Spontaneous Mutations – a mistake in base pairing during DNA replication. It occurs at random. • Mutagen – any agent that can cause a change in DNA • Ex. Chemicals, radiation, high temperatures

48. Repairing DNA • When mistakes do occur repair mechanisms fix mutations • Proofreading Enzymes – reads the DNA strand and checks it for mistakes • Repair Enzymes – fixes any mistakes in the DNA strand

49. Mistakes in Meiosis • Sometimes accidents occur during meiosis and chromosomes fail to separate correctly • Nondisjunction – failure of homologous chromosomes to separate • During meiosis I one chromosome from each pair is supposed to move to opposite poles but occasionally both chromosomes of a pair move to the same pole

50. Trisomy – 1 extra chromosome (47) • Ex: extra chromosome on pair number 21 – Down syndrome • Monosomy – missing 1 chromosome (45) • Ex: missing chromosome on pair number 23 – Turner syndrome • Tetraploid – 2 extra chromosomes (48) • Polyploids – organisms with more than the usual number of chromosome sets • Is rare in animals and almost always results in death.