UNIT 1 INFORMATION METHODS OF A CELL

What do you know about DNA? Building blocks are called? –nucleotides The shape is ? –Double helix The three primary components of a nucleotide are? –Sugar, phosphate, nitrogen base Where are each of these found? –The sugar and phosphate are in the backbone; the nitrogen base is on the rungs between DNA strands The sugar is? –deoxyribose

DNA RNA

DNA Backbone Structure Alternate phosphate and sugar (deoxyribose), phosphate ester bonds

DNA Backbone Structure Alternate phosphate and sugar (deoxyribose), phosphate ester bonds

DNA RNA

DNA Primary Structure Summary Backbone (sugar+phophate with phosphate ester bonds and base side chains)

DNA RNA

What are the base pairing rules for DNA?

DNA Double Helix Base pairing by unique hydrogen bonds C - G and A - T pairs

DNA Double Helix Base pairing by unique hydrogen bonds C - G and A - T pairs

Each strand of the double helix is oriented in the opposite direction What is this arrangement called? “Antiparallel “ Figure 10.5B 5 end3 end 5 end P P P P P P P P

What process is used in the cell to make new strands of DNA? DNA Replication

DNA

What do you remember? What does semi conservative replication mean? –The resulting DNA includes one original strand and one new strand –One original strand is “conserved” or saved.

Untwisting and replication of DNA each strand is a template for a new strand Figure 10.4B helicase DNA polymerase

What is the job of the helicase enzyme? –To unzip the DNA What is the job of the DNA polymerases? –To build new DNA strands by attaching nucleotides to the parent strand What is the job of ligase? –To attach fragments of DNA together

DNA Replication Complementary base pairs form new strands.

DNA polymerase works in only one direction 5 end P P Parental DNA Figure 10.5C DNA polymerase molecule Daughter strand synthesized continuously Daughter strand synthesized in pieces DNA ligase Overall direction of replication 5 3 Telomere sequences are lost with each replication. Cancer, aging telomeres

So what is a telomere anyway? A telomere is a repeating DNA sequence (for example, TTAGGG) at the end of the body's chromosomes. The telomere can reach a length of 15,000 base pairs. Telomeres function by preventing chromosomes from losing base pair sequences at their ends. They also stop chromosomes from fusing to each other. Each time a cell divides, some of the telomere is lost (usually base pairs per division). When the telomere becomes too short, the chromosome reaches a "critical length" and can no longer replicate. This means that a cell becomes "old" and dies by a process called apoptosis.

So what do telomeres have to do with Cancer? Its all about the enzyme, telomerase. Telomerase causes the continued addition of DNA ends (telomeres) so cells with active production of telomerase continue to grow and divide. Body cells no longer produce telemerase. What kind of cells keep growing and dividing? Fetal cells, tumor cells including cancer cells

DNA replication begins at many specific sites How can entire chromosomes be replicated during S phase of the cell cycle? Figure 10.5A Parental strand Origin of replication Bubble Two daughter DNA molecules Daughter strand What are these sites called? Replication Bubbles

DNA

In transcription, DNA helix unzips –RNA nucleotides line up along one strand of DNA, following the base-pairing rules –single-stranded messenger RNA peels away and DNA strands rejoin –What are the 3 steps of transcription? RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation Elongation Termination Area shown in Figure 10.9A Growing RNA RNA polymerase Completed RNA Figure 10.9B

DNA

RNA Transcription In nucleus, DNA guides the synthesis of mRNA

RNA Transcription RNA polymerase and elongation reaction

RNA Transcription RNA polymerase and elongation reaction

Eukaryotic RNA is processed before leaving the nucleus Noncoding segments, introns, are spliced out A cap and a tail are added to the ends Figure DNA RNA transcript with cap and tail mRNA ExonIntron Exon Transcription Addition of cap and tail Introns removed Exons spliced together Coding sequence NUCLEUS CYTOPLASM Tail Cap

RNA vs. DNA RNA contains Uracil, not Thymine Sugar is Ribose Usually single stranded Nitrogenous base (A, G, C, or U) Sugar (ribose) Phosphate group

Types of RNA mRNA contains codons which code for amino acids.

DNA

Types of RNA rRNA - Ribosome - contains enzymes and keeps everything together

Types of RNA tRNA - Transfer RNA carries amino acid and read codons on m-RNA through its own anticodons.

Types of RNA tRNA - Transfer RNA carries amino acid and read codons on m-RNA through its own anticodons.

Protein Synthesis

Check The following section of DNA is used to build a strand of mRNA 3’ – GAA- CCC- TTT- 5’ What is the corresponding mRNA sequesnce? What are the anticodons on the tRNA in the next step? Modified from

Summary of transcription and translation Figure Stage mRNA is transcribed from a DNA template. Anticodon DNA mRNA RNA polymerase TRANSLATION Enzyme Amino acid tRNA Initiator tRNA Large ribosomal subunit Small ribosomal subunit mRNA Start Codon 2 Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 3 Stage Initiation of polypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. TRANSCRIPTION

Figure (continued) 4 Stage Elongation Growing polypeptide Codons 5 Stage Termination mRNA New peptide bond forming Stop Codon The ribosome recognizes a stop codon. The poly- peptide is terminated and released. A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. Polypeptide