Semester 2: Unit 1: Molecular Genetics

Transcription

1 Semester 2: Unit 1: Molecular Genetics

2 Information Overload : Cells store information in DNA. Information is used to build molecules needed for cell growth. As cell size increases, the demands on that information (DNA) grow too.

3 Exchanging Materials: Food, oxygen, & water enter a cell through the cell membrane. Waste products leave the same way. The rate of exchange depends on the surface area of a cell. The rate at which nutrients are used up & waste products are produced depends on the cell s volume.

4 In multicellular organisms: -cell division leads to growth -allows organisms to repair & maintain its body In single-celled organisms: -cell division is a form of reproduction Before a cell grows too large, it divides into 2 new daughter cells= cell division. Before cell division, the cell copies all of its DNA so that each new cell receives a complete set of DNA

5 Chromatin- long strands of DNA wrapped around protein *genetic material of a non-dividing cell

6 Chromosomes- short, thick coiled up strands of DNA and protein *genetic material of a dividing cell Homologous chromosomesmatching or corresponding chromosomes; *one from each parent; in diploid cells

7 Mitosis- cell division that maintains the number of chromosomes to produce somatic (body) cells. *responsible for growth in multicellular organisms *produces diploid cells- cells with the same number of chromosomes as the ordinal parent cell 2n= 2 sets of chromosomes

8 Meiosis- cell division that reduces the number of chromosomes by half to produce gametes- sex cells *prodcues haploid cells- cells with half the number of chromosomes as the original parent cell n = 1 set of chromosomes

9 Sexual Reproduction: offspring are produced by the fusion of 2 sex cells (sperm & egg unite = fertilization ) 1 from each of 2 parents. fuse into a new single dipolid cell (zygote) the offspring grows by cell division offspring inherit DNA from both parents. carried out by animals & plants, & a few onecelled organisms

10 Cancer cells do not respond to signals that regulate growth and therefore divide uncontrollably. Cancer is a disorder in which body cells lose the ability to control cell growth. Cancer cells divide uncontrollably to form a mass of cells called a tumor. Cancers are caused by defects in genes that regulate cell growth & division. Some sources of gene defects are: -smoking tobacco -radiation exposure -defective genes -viral infection

11 A benign tumor is noncancerous. -does not spread to surrounding healthy tissue. A malignant tumor is cancerous. -invades & destroys surrounding healthy tissue -can spread to other parts of the body. The spread of cancer cells- metastasis Cancer cells: -absorb nutrients needed by other cells -block nerve connections -prevent organs from functioning.

12 DNA -a nucleic acid made of nucleotides joined into strands/chains by covalent bonds. DNA= Deoxyribonucleic Acid Each DNA nucleotide is made of 3 parts: 1-Deoxyribose sugar 2-Phosphate group (PO 4 ) 3-Nitrogenous base (1 of 4): purines: Adenine(A), Guanine(G) (2 rings) pyrimidines: Cytosine(C), Thymine(T) (1 ring)

13 The DNA that makes up genes must: 1-store information- instructions that cause a cell to develop 2-copy information- the structure of DNA (its H Bonds) is the key to how it being copied 3-transmit the genetic info- passing on critical info in DNA to new daughter cella.

14 Nucleotides join by covalent bonds between their sugar & phosphate groups. nitrogenous bases stick out sideways from the chain nucleotides can join together in any order

15 Chargaff s rules: amount of [A] = amount of [T] amount of [G] = amount of [C] Rosalind Franklin revealed an X-shaped pattern showing 2 strands in DNA twist around each other. *Also suggested the bases are near the center

16 Watson & Crick- The Double-Helix Model: build a 3-D model that explained the structure & properties of DNA model was a double helix- two strands wound around each other like a twisted ladder explains Chargaff s rules accounted for Franklin s X-ray pattern the 2 strands of DNA are antiparallel - they run in opposite directions bases to come in contact at center each strand carries a series of nucleotides

17 Watson & Crick discovered that hydrogen bonds form between certain bases in the center of the molecule, holding the 2 DNA strands together H bonds are weak chemical forces that allow the 2 strands of the helix to separate and rejoin which is critical to DNA replication H bonds would form only between base pairs- A with T, & G with C (base pairing). Watson & Crick realized base pairing explained Chargaff s rule, told why the # of [A]=[T] & [G]=[C].

18 12.2- The Structure of DNA Hydrogen Bonding: 2 hydrogen bonds between A and T 3 hydrogen bonds between G and C

19 12.2- The Structure of DNA DNA Double Helix: 2 strands need to TWIST around each other.

20 Before a cell divides, it duplicates its DNA in a copying process called replication. The Replication Process: Results in 2 DNA molecules identical to each other with each molecule having 1 original strand & 1 new strand

21 12.3- DNA Replication The Replication Process: 1. Untwist the DNA molecule 2. Unzip the two strands of the double helix-separate by breaking the H bonds between the base pairs replications forks allow complimentary bases to be brought in following the rules of base pairing 4. Rezip- new H bonds formed 5. Retwist BOTH DNA molecules

22 12.3- DNA Replication The Role of Enzymes: Helicase- untwists & unzips the DNA The principal enzyme involved in DNA replication is DNA polymerase. *Has 2 jobs: joins individual nucleotides to produce a new strand of DNA. also proofreads each new DNA strand, making sure that each molecule is an exact copy of the original.

23 12.3- DNA Replication In eukaryotic cells, replication begins at many places on the DNA molecule, proceeding in both directions until each chromosome is copied.

24 13.1- RNA RNA- Ribonucleic Acid - a long chain of nucleotides - uses the base sequence copied from DNA to direct the production of proteins

25 13.1- RNA Comparing RNA and DNA : DNA vs. RNA Deoxyribose sugar ribose sugar Double-stranded single-stranded Thymine base uracil base In nucleus nucleus & cytoplasm master plan blue print *both contain phosphate groups & the bases A, G, and C

26 The three main types of RNA: messenger RNA (mrna) ribosomal RNA (rrna) transfer RNA (trna) involved in protein synthesis; each has a specific role controls the assembly of amino acids into proteins.

27 13.1- RNA Messenger RNA: carry information from DNA to other parts of the cell carry copies of instructions for assembling amino acids into proteins

28 Ribosomal RNA: make up ribosomes along with proteins Ribosomes- the sites where proteins are assembled.

29 Transfer RNA: transfers each amino acid to the ribosome as it is specified by coded messages in mrna

30 RNA Synthesis: transcription- creating mrna from DNA segments of DNA serve as templates to produce complementary RNA molecules Prokaryotes- RNA synthesis & protein synthesis occur in the cytoplasm. Eukaryotes- RNA is produced in the nucleus & then moves to the cytoplasm to play a role in the production of proteins.

31 13.1- RNA Transcription: RNA polymerase- uses 1 strand of DNA as a template to assemble nucleotides into a complementary strand of mrna RNA polymerase binds only to promotersregions of DNA that show RNA polymerase exactly where to begin making RNA.

32 13.1- RNA Transcription: 1. Unwind & unzip DNA 2. Promoter binds RNA polymerase on DNA 3. RNA polymerase uses 1 DNA strand to make RNA 4. mrna breaks away & leaves nucleus 5. Rezip & rewind DNA

33 13.2- Ribosomes & Protein Synthesis Proteins are made by joining amino acids together into long chains- polypeptides. 20 different amino acids in polypeptides RNA contains bases: A, C, G, & uracil (U). These bases form a language, or genetic code, with just 4 letters : A, C, G, and U.

34 13.2- Ribosomes & Protein Synthesis The Genetic Code: Each three-letter word in mrna is known as a codon. A codon consists of 3 RNA bases that specify 1 amino acid to be added to the polypeptide chain.

35 13.2- Ribosomes & Protein Synthesis 4 different bases in RNA, there are 64 possible 3-base codons (4 4 4 = 64). Most amino acids can be specified by more than 1 codon. Methionine, AUG, is the start codon for protein synthesis mrna is read 3 bases at a time until a stop codon is reached ending translation

36 13.2- Ribosomes & Protein Synthesis AUG=start UGA=stop UAA=stop UAG= stop Pg. 367 in textbook

37 13.2- Ribosomes & Protein Synthesis Translation: sequence of bases in mrna= instructions of the order of amino acids joining to form a polypeptide Proteins formed from polypeptide chains Ribosomes assemble amino acids into polypeptide chains. decoding of an mrna message into a protein is translation.

38 13.2- Ribosomes & Protein Synthesis Steps in Translation: 1- mrna is transcribed in the nucleus & enters the cytoplasm 2- a ribosome attaches to mrna 3- ribosome reads each mrna codon & directs trna to bring specific amino acid to the ribosome 4- ribosome attaches amino acid to chain

39 13.2- Ribosomes & Protein Synthesis Steps in Translation: Step 1 Step 2 Step 3 Step 4

40 13.2- Ribosomes & Protein Synthesis trna: each trna carries 1 kind of amino acid each trna molecule has 3 unpaired bases- anticodon- is complementary to the mrna codon. Ex: anticodon UAC pair with the codon AUG

41 13.2- Ribosomes & Protein Synthesis Ribosome forms a peptide bond between the amino acids bond holding the first trna molecule to its amino acid is broken; trna leaves ribosome moves down to next codon, and trna brings in amino acid specified by the codon

42 13.2- Ribosomes & Protein Synthesis polypeptide chain grows until a stop codon is reached ribosome releases the polypeptide & the mrna molecule, completing translation

43 Mutations- heritable changes in genetic info (DNA) Cells may make mistakes copying DNA Gene Mutations: point mutations- involve changes in 1 or a few nucleotides occur at a single point in the DNA sequence If a gene in 1 cell is altered, it can be passed on to every developing cell. Types: substitutions, insertions, deletions

44 Substitutions- 1 base is changed to a different base affect only 1 amino acid or NO effect.

45 13.3- Mutations Gene Mutations: Insertions- 1 base is inserted (added) into the DNA sequence. Deletions- 1 base is removed from the DNA sequence.

46 13.3- Mutations Gene Mutations: Insertions & Deletions result in frameshift mutations shift the reading frame of the genetic message- read 3 bases at a time, but shifts every codon that follows the mutation can change every amino acid that follows the point of the mutation, & alter a protein that its unable to perform its function.

47 13.3- Mutations Chromosomal Mutations: Deletion- involves the loss of all or part of a chromosome. *Part B of the chromosome is lost or deleted

48 13.3- Mutations Chromosomal Mutations: Duplication- produces an extra copy of all or part of a chromosome *Part B was doubled and added in to chromosome

49 13.3- Mutations Chromosomal Mutations: Inversion- reverses the direction of parts of a chromosome. *parts B and C were reversed or flip-flopped

50 13.3- Mutations Chromosomal Mutations: Translocation- occurs when part of one chromosome breaks off and attaches to another. *Part GH is added in from another chromosome

51 13.3- Mutations Effects of Mutations: Mutagens- chemical or physical agents in the environment that cause mutations Chemical: certain pesticides, tobacco smoke, & environmental pollutants Physical: X-rays & ultraviolet light Effects of mutations on genes vary: -little or no effect on organism -beneficial- resist pesticides; polyploid crops -negative- cancer or disease