DNA, RNA & PROTEINS The molecules of life

DNA Deoxyribonucleic Acid (DNA) is the blueprint for life:

DNA structure DNA is a polymer of nucleotides Each nucleotide composed of _________________ _________________ _________________

Four DNA bases Four kinds of nitrogenous bases: Purine bases Pyrimidine bases

DNA: Complimentary base pairing Adenine pairs with ________ A Cytosine pairs with _________ C

DNA STRUCTURE DNA is a ________ helix Discovered by Watson and Crick

DNA REPLICATION (in the nucleus)

DNA Replication First an enzyme DNA topoisomerase untangles the coils Next: Enzymes called “Helicase” “unzip” the DNA molecule exposing both strands nitrogenous bases. The DNA is separated into two strands.

DNA Replication Then: (enzyme) DNA polymerase pairs the bases A-T and G-C. DNA Polymerase checks work and corrects mistakes …. Nucleotides are paired   DNA ligase (enzyme) follows behind and bonds the nucleotides together. Two strands of DNA are created.

DNA Replication The process is fast and accurate an error occurs in only about one of a billion nucleotides.

DNA replication begins at specific sites called origins of replication. The copying proceeds outward in both directions, creating replication "bubbles". The parent DNA strands open up as daughter strands grow on both sides of each bubble.

A eukaryotic DNA molecule has many origins where replication can start at the same time. This shortens the total time to copy all the DNA. Eventually, all the bubbles merge End product: two double-stranded DNA molecules, each with one new and one old strand.

DNA replication occurs before a cell divides, ensuring that the cells in a multicellular organism all carry the same genetic information. It is also the mechanism for producing the DNA copies that offspring inherit from parents during reproduction.

DNA replication The resulting double-stranded DNA molecules are identical; proofreading and error-checking mechanisms exist

RNA structure and synthesis RNA: RIBONUCLEIC ACID Is very similar to DNA (repeating subunits, nucleotides). Difference between RNA and DNA: 1. Each nucleotide contains a different sugar: RIBOSE instead of deoxyribose. 2. Bases are A, G, C, and U (URACIL) A pairs with U; G pairs with C

RNA 3. RNA is single stranded and shorter

CENTRAL DOGMA DNA RNA Proteins transcription DNA RNA Proteins 3 different RNA molecules involved in protein synthesis: mRNA (messenger RNA) rRNA (ribosomal RNA tRNA (transfer RNA) translation

PROTEIN SYTNESIS 1 step: Transcription occurs in the nucleus 2 step: Translation occurs in the cytoplasm

1st step Transcription: DNA  RNA Transcription occurs in the nucleus First: DNA unwinds in a section Next: mRNA (messenger RNA) is formed by base pairing with the parent strand of DNA. This begins transcription. Then: mRNA carries the message about what type of protein to make from the DNA in the nucleus to the ribosome

Transcription Once mRNA is formed, enzymes in the nucleus remove the Introns (noncoding message) and leave the Exons (good message)

The Genetic Code Each 3 consecutive bases on the mRNA is a code word, CODON, that specifies an amino acid. The genetic code consists of 64 codons, but only 61 code amino acids. Three codons act as signal to stop the process One codon, AUG, codes for methionine, and is also the Start signal for translation.

2nd step Translation: RNA  Protein Translation: synthesizing a code from amino acids, according to the sequences of the nucleotides in mRNA. Occurs at the ribosome, in cytoplasm of cell Ribosomal RNA, rRNA, is needed for protein synthesis – helps mRNA bind to the ribosome tRNA, brings specific amino acids to the ribosome to be assembled as proteins.

Translation Ribosomes are the sites of ______________

Transfer RNA (tRNA) Transport molecule that carries specific amino acid to a ribosome Each tRNA recognizes the correct codon on the mRNA molecule

Translation

Steps in Translation mRNA leaves the nucleus and migrates to ribosome mRNA binds to small ribosomal subunit tRNA brings an amino acid to the ribosome, where anticodon on the tRNA binds to the codon of the mRNA The amino acid bonds to its adjoining amino acid to form a growing polypeptide molecule The tRNA without the amino acid is released from the ribosome Other tRNA’s bring amino acids to the ribosome to complete the protein molecule

Protein translation

Protein synthesis Occurs in the cytoplasm of the cell

Summary:

Important Both DNA and RNA have a direction: one end is the 3’ the other is the 5’ end. Thus, codons are read in one direction only. Also, note there is redundancy in the genetic code: the different sequences can specify for the same amino acid. Example: _______________= Leucine

When things go wrong… Mutations: changes in the DNA sequence, that may be passed along to future generations. Point mutations: a single base substitution THE CAT SAW THE RAT THE CAT SAW THE HAT Deletion: a small DNA segment is lost Insertion: a segment of DNA is added Frame-shift mutation: modification of the reading frame after a deletion or insertion, resulting in all codons downstreams being different.

Somatic Mutations ___________ mutations: occur in body cells, or cells that do not lead to gametes. Somatic mutations that occur in leaves, roots or stems are usually not passed on to future generations… UNLESS the plant reproduces ____________