* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download File
DNA sequencing wikipedia , lookup
Expanded genetic code wikipedia , lookup
Biochemistry wikipedia , lookup
Holliday junction wikipedia , lookup
Agarose gel electrophoresis wikipedia , lookup
Polyadenylation wikipedia , lookup
Messenger RNA wikipedia , lookup
Maurice Wilkins wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Genetic code wikipedia , lookup
Community fingerprinting wikipedia , lookup
Molecular evolution wikipedia , lookup
RNA polymerase II holoenzyme wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Bisulfite sequencing wikipedia , lookup
Non-coding RNA wikipedia , lookup
Epitranscriptome wikipedia , lookup
Gel electrophoresis of nucleic acids wikipedia , lookup
Molecular cloning wikipedia , lookup
Gene expression wikipedia , lookup
Transcriptional regulation wikipedia , lookup
Eukaryotic transcription wikipedia , lookup
Non-coding DNA wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Cre-Lox recombination wikipedia , lookup
DNA supercoil wikipedia , lookup
Use the guided notes sheet to make notes on the Primary – Tertiary structure of proteins on page 29 and then Fibrous and Globular proteins on page 31. All students will be able to describe the structure of DNA All students should be able to outline how DNA replicates All students could explain the function of the enzymes involved in replication DNA is made up of a chain of nucleotides Each nucleotide is comprised of a pentose sugar (deoxyribose in DNA, ribose in RNA) a phosphate a nitrogen containing base – adenine, thymine, guanine, cytosine The phosphate alternates with the deoxyribose sugar to form the backbone. It attaches to the OH groups at carbons 3 and 5 on the sugars to form phosphodiester bonds between them Two complementary chains are held together by weak forces. The two chains run in opposite directions Bases are inside the helix because they are hydrophobic A forms 2 hydrogen bonds with T G forms 3 hydrogen bonds with C Covalent bonds hold nucleotide together Phosphodiester bond (covalent) holds sugar phosphate backbone together This bond is made by a condensation reaction Hydrogen bonding between complementary base pairs holds the 2strands together Strands run anti-parallel – one is ‘upside down’ Happens during interphase DNA copying needs to be accurate so the genetic code can be passed correctly Helicase enzyme unwinds the helix and unzips the strands by breaking H bonds The strands of DNA act as templates for the new strands DNA replication is semi-conservative – what does this mean? Helicase RNA primase DNA polymerase III DNA polymerase I DNA ligase State a role for each of four different named enzymes in DNA replication. (Total 6 marks) Award [1] for any two of the following up to [2 max]. helicase; DNA polymerase / DNA polymerase III; RNA primase; DNA polymerase I; (DNA) ligase; 2 max Award [1] for one function for each of the named enzymes. helicase: splits / breaks hydrogen bonds / uncoils DNA / unwinds DNA; (DNA) polymerase III: adds nucleotides (in 5' to 3' direction) / proofreads DNA; (RNA) primase: synthesizes a short RNA primer (which is later removed) on DNA; 5. (DNA) polymerase I: replaces RNA primer with DNA; (DNA) ligase: joins Okazaki fragments / fragments on lagging strand / makes sugar-phosphate bonds between fragments; 4 max [6] Helicase holds the two strands apart Free floating nucleotides line up with the bases on the strands through complementary base pairing H bonds form between bases to hold nucleotide in place DNA polymerase catalyses condensation reaction between sugars and phosphates to form new backbone Now have two new strands of DNA that coil into a helix DNA polymerase proof reads molecule to make sure no mistakes have occurred The primer allows DNA polymerase III to bind and start replication DNA polymerase I removes the RNA primers and replaces them with DNA RNA primase adds short sequences of RNA to both strands (the primer) DNA ligase then joins the Okazaki fragments together to form a continuous strand One strand is replicated in a continuous manner in the same direction as the replication fork (leading strand) DNA polymerase III adds nucleotides to each template strand in a 5'→3' direction These nucleotides are initially deoxyribonucleoside triphosphates but they lose two phosphate groups during the replication process to release energy The other strand is replicated in fragments (Okazaki fragments) in the opposite direction (lagging strand) Helicase uncoils the DNA Helicase uncoils the DNA RNA primase adds short sequences of RNA to both strands (the primer) The primer allows DNA polymerase III to bind and start replication DNA polymerase III adds nucleotides to each template strand in a 5'→3' direction These nucleotides are initially deoxyribonucleoside triphosphates but they lose two phosphate groups during the replication process to release energy One strand is replicated in a continuous manner in the same direction as the replication fork (leading strand) The other strand is replicated in fragments (Okazaki fragments) in the opposite direction (lagging strand) DNA polymerase I removes the RNA primers and replaces them with DNA DNA ligase then joins the Okazaki fragments together to form a continuous strand Explain the significance of complementary base pairing. 5marks when DNA replicates the 2 strands separate; each single strand acts as template for base-pair matching; free nucleotides of adenine bond only with thymine nucleotides of cytosine bond only with guanine; This copies the opposite strand of the original DNA molecule; replication is semi-conservative; original order of bases is maintained; new DNA identical to parent molecule; significance of base-pair matching is that the information encoded in one DNA molecule is passed to others 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. What 3 things make up a nucleotide? Name the 4 bases Which bases pair up? What forms the back bone of the DNA? In which direction does the DNA polymerase add new nucleotides? What bonds hold the sugar and phosphate together? What bonds hold the 2 strands of DNA together? What enzyme adds the new nucleotides to the ? DNA replication is ______--______ What unwinds and unzips the helix? The DNA double helix contains major and minor grooves on its outer diameter, which expose chemical groups that can form hydrogen bonds The DNA of eukaryotes associates with proteins called histones DNA is wound around an octamer of histones (146 bases and 1.65 turns of the helix per octamer) The octamer and DNA combination is secured to a H1 histone, forming a nucleosome Nucleosomes serve two main functions: They protect DNA from damage They allow long lengths of DNA to be packaged (supercoiled) for mobility during mitosis / meiosis When supercoiled, DNA is not accessible for transcription Cells will have some segments of DNA permanently supercoiled (heterochromatin) and these segments will differ between different cell types 7.1.4 Distinguish between unique or single copy genes and highly repetitive sequences in nuclear DNA 7.1.5 State that eukaryotic genes contain introns and exons Intron: A non-coding sequence of DNA within a gene (intervening sequence) that is cut out by enzymes when RNA is made into mature mRNA Exon: The part of the gene which codes for a protein (expressing sequence) •Eukaryotic DNA contains introns but prokaryotic DNA does not (a) two genetically identical nuclei/daughter cells formed during mitosis (so hereditary information in DNA can be passed on); two copies of each chromosome/DNA molecule/chromatid needed; helicase unwinds the DNA/double helix; to allow the strands to be separated; helicase separates the two (complementary) strands of DNA; by breaking hydrogen bonds between bases; [4 max] (b) DNA replication is semi-conservative; DNA is split into two single/template strands; nucleotides are assembled on/attached to each single/template strand; by complementary base pairing; adenine with thymine and cytosine with guanine / A with T and C with G; strand newly formed on each template strand is identical to other template strand; DNA polymerase used; [5 max] Marks may be awarded for any of the above points if clearly presented in a well-annotated diagram. (c) hydrogen bonds between nucleotides of opposite strands/complementary bases/adenine and thymine and cytosine and guanine; covalent bonds between nucleotides within strands/between sugar/deoxyribose and phosphate; 7. (a) Draw a labelled diagram to show how two nucleotides are joined together in a single strand of DNA. [3] Objectives: 7.3.1 – State that transcription is carried out in a 5’ 3’ direction 7.3.2 – Distinguish between the sense and antisense strands of DNA 7.3.3 – Explain the process of transcription in prokaryotes, including the role of the promoter region, RNA polymerase, nucleoside triphosphates and the terminator. 7.3.4 – State that eukaryotic RNA needs the removal of introns to form mature mRNA Similar to replication in that it is carried out in the 5’ to 3’ direction. Helicase not involved RNA polymerase separates the 2 strands of DNA RNA polymerase only allows synthesis of RNA in the 5’-3’ direction Promoter (start) Transcription unit Terminator (stop) The terminator is a sequence of nucleotides that, when transcribed, causes the RNA polymerase to detach from the DNA. The transcript that carries the code of the DNA is called messenger RNA (mRNA). Transcription continues beyond the terminator fro a number of nucleotides. Eventually it is released from the DNA strand. NTPs (Nucleoside triphosphates) containing 3 phosphates and the 5-carbon sugar ribose, are paired with the appropriate bases of the antisense strand. mRNA is synthesis with the help of RNA polymerase and the release of 2 phosphates from NTP. This is often referred to as ELONGATION. Eukaryotic DNA is different from prokaryotic DNA in that within the protein coding regions there are stretches of non-coding DNA. These regions are called introns. To make a functional mRNA strand from eukaryotes, the introns are removed. Prokaryotic mRNA does not require processing because no introns are present. Use the worksheet provided to annotate and make notes as the animation progresses. A. Sigma factor helps to transport RNA polymerase to promoter region B. In eukaryotes the introns are removed from the mRNA leaving only the exons. C. RNA polymerases polymerises RNA in the 5’ 3’ direction D. NTPs are pairs with the appropriate DNA bases and 2 phosphates are released to provide energy for the pairing E. In prokaryotes the terminator region of the F. RNA polymerase binds to DNA at promoter region A. Sigma factor helps to transport RNA polymerase to promoter region C.RNA polymerases polymerises RNA in the 5’ 3’ direction D. NTPs are pairs with the appropriate DNA bases and 2 phosphates are released to provide energy for the pairing E. In eukaryotes the introns are removed from 7.4.1 Explain that each tRNA molecule is recognised by a tRNA-activating enzyme that binds a specific amino acid to the tRNA using ATP for energy 7.4.2 Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites and mRNA binding sites 7.4.3 State that translation consists of initiation, elongation, translocation and •Ribosomes are made of protein (for stability) and ribosomal RNA (rRNA - for catalytic activity) •They consist of two subunits: • The small subunit contains an mRNA binding site • The large subunit contains three tRNA binding sites an aminacyl (A) site, a peptidyl (P) site and an exit (E) site •Ribosomes can be either found freely in the cytosol or bound to the rough ER (in eukaryotes) •Ribosomes differ in size in eukaryotes and prokaryotes (eukaryotes = 80S ; prokaryotes = 70S) Translation occurs in four main steps: Initiation: Involves the assembly of an active ribosomal complex Elongation: New amino acids are brought to the ribosome according to the codon sequence Translocation: Amino acids are translocated to a growing polypeptide chain Termination: At certain "stop" codons, translation is ended and the polypeptide is A. Translation is initiatied by formation of an initiation complex consisting of the smaller ribosomal subunit, the first amino acid-tRNA and mRNA. B. The ribsome dissociates into the smaller and larger subunits and the messenger RNA and protein are released. C. The larger ribosomal subunit then joins the complex. Proteins called initiation factors are involved but aren’t shown in the diagram. D.Elongation of the polypeptide is terminated when the ribsome reachesa codon that does not for an amino acid, called a stop codon. E. The 70s ribosome has 2 sites to which transfer RNAcarrying amino acids can bind. One is called the A. Translation is initiatied by formation of an initiation complex consisting of the smaller ribosomal subunit, the first amino acid-tRNA and mRNA. C. The larger ribosomal subunit then joins the complex. Proteins called initiation factors are involved but aren’t shown in the diagram. E. The 70s ribosome has 2 sites to which transfer RNA-carrying amino acids can bind. One is called the peptidyl or P site and the other is called the acceptor or A site. H. The amino acid carried by the transfer RNA in the P site is then joined to the amino acid carried by the transfer RNA that just entered the A site. F. The ribsome now advances a distance of one 7.4.6 Explain the process of translation, including ribosomes, polysomes, start codons and stop codons 7.4.7 State that free ribosomes synthesise proteins for use primarily within the cell, and that bound ribosomes synthesise proteins primarily for secretion or for lysosomes Initiation: The small ribosomal subunit binds to the 5' end of mRNA and moves along until it reaches the start codon (AUG) Next, the appropriate tRNA molecule binds to the codon via its anticodon (according to complementary base pairing) Finally, the large ribosomal subunit aligns itself to the tRNA molecule at its P-site and forms a complex with the small ribosomal subunit A second tRNA molecule pairs with the next codon in the ribosomal A-site The amino acid in the P-site is covalently attached via a peptide bond to the amino acid in the A-site The ribosome moves along one codon position, the deacylated tRNA moves into the E-site and is released, while the tRNA bearing the dipeptide moves into the P-site Another tRNA molecules attaches to the next codon in the newly emptied A-site and the process is repeated The ribosome moves along the mRNA sequence in a 5' - 3' direction, synthesising a polypeptide chain Elongation and translocation continue until the ribosome reaches a stop codon These codons do not code for any amino acids and instead signal for translation to stop The polypeptide is released and the ribosome disassembles back into subunits The polypeptide may undergo posttranslational modification prior to becoming a functional protein Ribosomes floating freely in the cytosol produce proteins for use within the cell Ribosomes attached to the rough ER are primarily involved in producing proteins to be exported from the cell or used in the lysosome These proteins contain a signal recognition peptide on their nascent polypeptide chains which direct the associated ribosome to the rough ER