KEY CONCEPT DNA structure is the same in all organisms.

We love D N A Made of nucleotides Sugar, Phosphate and a Base Bonded down one Side Adenine and Thymine Make a Lovely Pair Cytosine without Guanine Would feel very bare O-O-O deoxy-ribo-nucleic acid R-N-A is ribo-nucleic acid

DNA is made up of a long chain of nucleotides. Each nucleotide has three parts. a sugar – deoxyribose phosphate group a nitrogen-containing base phosphate group deoxyribose (sugar) nitrogen-containing base

The nitrogen containing bases - Adenine (A) - Thymine (T) - Cytosine (C) - Guanine (G)) * Purines – have 2 rings = Adenine & Guanine * Pyrimidines – have 1 ring = Cytosine & Thymine

Watson and Crick determined the three-dimensional structure of DNA 1953 Two nucleotide chains that wrap around each other to form a double spiral (double helix) - Temperature liable – a change in T can break apart the DNA strand

Rosalind Franklin and Erwin Chargaff. Franklin’s x-ray images suggested that DNA was a double helix of even width. Chargaff’s - Complementary Base Pairing - A=T and C=G.

Nucleotides always pair in the same way. Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. A-T C-G C G T A

The backbone is connected by covalent bonds. The bases are connected by hydrogen bonds. hydrogen bond covalent bond

8.3 DNA Replication KEY CONCEPT DNA replication copies the genetic information of a cell.

The rules of base pairing direct replication. 8.3 DNA Replication The rules of base pairing direct replication. A-T G-C DNA is replicated during the S stage of interphase. Happens inside the nucleus

DNA serves as a template. 8.3 DNA Replication DNA serves as a template. 1. Helicase – enzyme that breaks the Hydrogen bonds between the bases Replication Fork – point at which the two chains separate (last bond broken) nucleotide The DNA molecule unzips in both directions.

8.3 DNA Replication New complimentary nucleotide bases pair up on both sides of old DNA template DNA polymerase (enzyme) forms new Hydrogen bonds between the nucleotides DNA polymerase new strand nucleotide

8.3 DNA Replication Two new exact copies of DNA are formed, each with an original strand and a newly formed strand. original strand new strand Two molecules of DNA

Replication is fast and accurate. 8.3 DNA Replication Replication is fast and accurate. DNA replication starts at many points in eukaryotic chromosomes. There are many origins of replication in eukaryotic chromosomes. Mutation – change in the nucleotide sequence DNA polymerases can find and correct errors. Error Rate - one error per 1 billion nucleotides

8.4 Transcription RNA differs from DNA in three major ways. RNA – sugar = ribose 2. RNA has uracil instead of thymine. U - A 3. RNA is a single-stranded structure.

8.4 Transcription Three types of RNA. Mesenger RNA (mRNA) – single uncoiled chain carries genetic information from the DNA in the nucleus to the cytoplasm Transfer RNA (tRNA) – single chain of about 80 nucleotides folded into a hairpin shape binds to specific amino acids Ribosomal RNA (rRNA) – makes up the ribosomes where proteins are made

8.4 Transcription Process of copying DNA into mRNA Transcription starts when RNA polymerase – (enzyme) binds to a Promoter on DNA RNA polymerase breaks H-bonds and makes H-bonds One chain is used as a template (mRNA = transcript) Transcription stops when RNA polymerase reaches a terminator start site nucleotides transcription complex

Transcription vs Replication. Replication copies all the DNA; transcription copies a gene. growing RNA strands DNA one gene

8.5 Translation KEY CONCEPT Translation converts an mRNA message into a protein.

Amino acids are coded by mRNA base sequences. 8.5 Translation Amino acids are coded by mRNA base sequences. Codon – 3 nucleotides of mRNA AUG = start UAA, UAG, UGA = stop codon for methionine (Met) leucine (Leu)

8.5 Translation The genetic code matches each codon to its amino acid

8.5 Translation tRNA – transports amino acids to the ribosomes Anticodon – tRNA sequence of 3 nucleotides complementary to an mRNA codon.

8.5 Translation Translation takes place at the Ribosomes Ribosomes that are attached to the endoplasmic reticulum build proteins for use outside cell Ribosomes that are free floating make proteins for use inside cell

8.5 Translation For translation to begin - Ribosomes attaches to a start codon on mRNA (AUG) Start codon pairs with the anticodon on tRNA (UAC) codes for the first amino acid – methionine – may be removed later if not needed

8.5 Translation Amino acids are bonded together with peptide bonds

8.5 Translation Once the stop codon is reached, the ribosome releases the protein

8.6 Gene Expression and Regulation KEY CONCEPT Gene expression is carefully regulated in both prokaryotic and eukaryotic cells.

8.6 Gene Expression and Regulation A promotor is a DNA segment that allows a gene to be transcribed. An operator is a part of DNA that turns a gene “on” or ”off.” The lac operon was one of the first examples of gene regulation to be discovered. has three genes that code for enzymes that break down lactose – milk sugar

8.6 Gene Expression and Regulation RNA processing Introns are nucleotides that are removed from mRNA Exons are the nucleotides that are spliced together. Processed mRNA (transcript) goes to ribosome to be made into a protein

8.6 Gene Expression and Regulation Coding DNA (genes)  make proteins Humans = 20,000 Non-coding DNA (genes)  make RNA (transcribed but never translated) Human = 500 Human Total = ~ 20,500 genes