3 very important cell processes: DNA Replication Transcription Translation

DNA Replication Happen in the cell’s nucleus When a cell divides, the two daughter cells need a copy of the original cell’s DNA Makes an exact copy of the original DNA molecule C matches with G (or G with C) A matches with T (or T with A) Check this out: http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html

Transcription Message (or code) of DNA nucleotide sequences copied from DNA to mRNA (messenger RNA) C on DNA matches with G on mRNA (or G on DNA matches with C on mRNA T on DNA matches with A on mRNA (or A on DNA matches with U on mRNA) Completed mRNA carries message from DNA and leaves the cell nucleus to the cytoplasm (at the ribosomes) where next process occurs (translation)

Translation Message from mRNA (order of nucleotides came from DNA) is translated to a specific protein tRNA (transfer RNA) looks for a specific amino acid (ex: leucine) in the cytoplasm that it can take to the ribosome to join with a certain codon (3 letter mRNA sequence), joining other amino acids to form a polypeptide (protein) tRNA then free to find more of the same amino acid to make more protein

Questions 1-3, p 233 How many types of nucleotides are in DNA , and how do they differ? Four, their nitrogen-containing bases differ How are the base pairing rules related to Chargaff’s research on DNA? Because only A pairs with T and C pairs with G, DNA will always have approximately the same proportion of A and T and same proportion of C and G. Explain how the double helix model of DNA built on the research of Rosalind Franklin. - Franklin’s data suggested that DNA was a helix made of two strands an even width apart. From this, Watson and Crick realized that a base with one ring would bond with the base with two rings.

Questions 4-6, p 233 Infer – Which part of a DNA molecule carries the genetic instructions that are unique for each individual: the sugar-phosphate backbone or nitrogen-containing bases? Explain. The backbone is the same in all DNA. The nitrogen-containing bases provide the unique instructions. Predict – In a sample of yeast DNA, 31.5% of the bases are adenine (A). Predict the approximate percentage of C, G, and T. Explain. Matching A, T, is approximately 31.5 percent. Thus, C and G together make up 37 percent of the bases, so each makes up approximately 18.5 percent of the bases. Evolution – The DNA of all organisms contain the same four bases (adenine, thymine, cytosine and guanine). What might this similarity indicate about the origins of life on Earth? It suggests that the wide diversity of life that we see might have stemmed from a common ancestor.

Questions 1-3, p 238 Explain the function of replication. To make a copy of all of the DNA in a cell so it can be passed on to a new cell. Explain how DNA serves as its own template during replication. Both strands act as a template. Because base pairing is specific, the sequence of one strand dictates what the sequence of the other strand has to be. How do cells help ensure that DNA replication is accurate? Certain types of DNA polymerase have a built in proofreading function that corrects most mispaired nucleotides.

Questions 4-6, p 238 Summarize – Describe two major functions of DNA polymerase. DNA polymerase bond nucleotides together and proofread to ensure accuracy. Infer – Why is it important that human chromosomes have many origins of replication? Each chromosome in a eukaryotic cell is very long. If replication started at only one place, it would take a very long time to finish. Multiple origins of replication let the process happen more quickly. Cell Biology – DNA is replicated before mitosis and meiosis. How does the amount of DNA produced in a cell during mitosis compare with that produced during meiosis? Cells produced by mitosis typically have twice the amount of DNA as cells produced by meiosis.

Questions 1-3, p 242 What is the central dogma? - It is a statement that summarizes how information flows in one direction from DNA to RNA to proteins. Why can the mRNA strand made during transcription be thought of as a mirror image of the DNA strand from which it is made? The mRNA chain is complementary to the DNA molecule. Like a mirror image, the mRNA chain has a distinct relationship to the DNA molecule, but it is not identical to it. Why might a cell make lots of rRNA but only one copy of DNA? - rRNA is a component of ribosomes, and many ribosomes are needed to keep up with the level of protein synthesis needed by a cell. In contrast, each cell needs only one set of DNA, so it is copied only in preparation for cell division.

Questions 4-5, p 242 Apply – If a DNA segment has the nucleotide AGCCTAA, what would be the nucleotide sequence of the complementary RNA strand? UCGGAUU Synthesize – What might geneticists learn about genes by studying RNA? - Because mRNA codes for only a single gene, studying mRNA can help researchers learn where genes begin and end on a chromosome. It could also indicate what genes are active in specific types of cells.

Questions 1-3, p 247 Explain the connection between a codon and an amino acid. A codon is a sequence of three nucleotides that specifies a specific amino acid. Students may describe the physical connection between these two as the tRNA molecule. Each tRNA molecule binds to a specific amino acid and has an anticodon that binds to a specific codon. Briefly describe how the process of translation is started. The small ribosomal sub-unit binds to the mRNA strand at the start codon, which binds to the first tRNA molecule. Synthesize – Suppose a tRNA molecule had the anticodon AGU. What amino acid would it carry? That tRNA molecule would recognize the mRNA codon UCA, so it would carry the amino acid serine.

Questions 4 & 5, p 247 Hypothesize – The DNA of eukaryotic cells has many copies of genes that code for RRNA molecules. Suggest a hypothesis to explain why a cell needs so many copies of these genes. rRNA is critical for making ribosomes to carry out protein synthesis. rRNA must be made in sufficient quantities to keep up with a cell’s demands for various proteins. Biochemical Reactions – Enzymes have shapes that allow them to bind to a substrate. Some types of RNA also form specific three-dimensional shapes. Why do you think that RNA, but not DNA catalyzes biochemical reactions? DNA is usually in double-stranded form, wrapped up and condensed to make it compact, not in a catalytic form. In contrast, hydrogen bonds form between the nucleotides of a single strand of RNA, causing it to form a catalytic structure.