DNA and RNA

DNA is Made of subunits called nucleotides (monomer) Each nucleotide contains a phosphate group a 5-carbon sugar (deoxyribose) and a nitrogen base You will make this In your animation!

Structure of DNA DNA is shaped like a ladder A twisted ladder made of 2 sides. Sides: deoxyribose and phosphate groups. “Steps:” nitrogen base pairs. Because the ladder is twisted, the shape of DNA is referred to as a double helix.

The Base Pair Rule (Chargaff’s Rule) Adenine always pairs with thymine. Guanine always pairs with cytosine.

The percentage of guanine and cytosine in a cell are almost equal. The percentage of adenine and thymine are almost equal. The amount of purines = amount of pyrimadines.

The search for structure Rosalind Franklin—x-ray diffraction to study the shape of DNA James Watson and Francis Crick—double helix model of DNA 1962 Nobel Prize

Where in the cell is DNA? Eukaryotic cells—nucleus Prokaryotic cells—cytoplasm Regardless of location, DNA provides the “blueprint” for producing the organism.

Chromatin consists of DNA and RNA Sections of DNA, called genes, contain instructions for assembling proteins.

Why must DNA replicate? Every time a cell reproduces, DNA must be copied or replicated. Without DNA replication organisms could not grow and reproduce. DNA replication is making an 2 identical copies of your DNA!

DNA Replication Enzymes break the hydrogen bonds between the nitrogen base pairs. The “ladder” separates. Brown: Original DNA strand Blue: New strands being formed

Hydrogen Bonds

DNA Replication Continues Free nucleotides bond to each strand, following the base pair rule. The new strands are identical to the original molecule. Each copy of DNA has one new and one original strand.

How Does DNA Work? Genes are encoded DNA instructions to make proteins. DNA stays in the nucleus. But proteins are made at the ribosomes…..

RNA Carries the Code Because DNA cannot leave the nucleus, the genetic code must be transcribed into RNA. RNA stands for ribonucleic acid.

RNA Structure RNA is composed of a single strand of nucleotides instead of two strands. RNA contains ribose instead of deoxyribose. RNA contains uracil (U) instead of thymine (T.)

Types of RNA Messenger RNA(mRNA): copies DNA code and carries it to the ribosome Ribosomal RNA(rRNA): makes up part of the ribosome Transfer RNA(tRNA):transfers amino acids to the ribosome

Protein Synthesis Step 1: Transcription DNA code is copied into Messenger RNA DNA Base Pairs with this RNA Base Cytosine Guanine Thymine Adenine Uracil Once the DNA code is copied, mRNA leaves the nucleus and travels to the ribosome.

Protein Synthesis Step 2: Translation mRNA arrives at the ribosome. tRNA brings amino acids to the ribosome. Amino acids are joined together to form a protein.

Amino Acid to Protein Recall, proteins are made of amino acids. There are 20 different amino acids. How does tRNA know which amino acids are needed?

The Genetic Code The genetic code is read three letters at a time. Each set of three nitrogen bases represents a specific amino acid and is called a codon. 64 combinations are possible.

Codon Chart UUU = phenylalanine UGG = tryptophan AAC = asparagine

Codon Chart UUU = phenylalanine UGG = tryptophan AAC = asparagine

Keep to the code Codons code for only one amino acid. CCG always codes for proline. An amino acid can have more than one codon. AGC and AGU both code for serine.

tRNA tRNA has an anticodon that matches with the mRNA codon. This ensures that the correct amino acid is added to the protein chain.

Mutation – When mistakes are made Any mistake or change in the DNA sequence is called a mutation.

Types of Mutations Gene Mutations Point Mutations Frameshift Mutations Chromosomal Mutations Deletions Duplications/Amplifications Inversions Insertions Translocations

Point Mutations A point mutation occurs when a single base pair changes. Point mutations are also called substitutions.

Effects of Substitutions With a substitution, usually only one amino acid is affected. This can change the entire structure of a protein OR have no effect at all.

Point Mutation/ Substitution

Frameshift Mutations The addition or deletion of a nitrogen base is called a frameshift mutation. Every amino acid after the mutation may be affected. Proteins may be unable to perform normal functions.

Frameshift Mutation: Deletion

Chromosomal Mutations Chromosomal mutations affect multiple genes and involve changes in the number or structure of chromosomes.

Result of Mutations Causes of Mutations Usually random events Other causes: Exposure to X-rays Ultraviolet rays Radioactive substances Chemicals Result of Mutations 1. Birth defects 2. Cancer

Effects of Mutations Mutations occur in all living organisms. If a mutation does not change the amino acid sequence, it is called a silent mutation. Ex. CCG  CCC still codes for proline Mutations that change the amino acid sequence may be harmful or beneficial.

Source of Genetic Variability Mutations are the ultimate source of genetic variability. According to the theory of evolution, it is through mutations that species evolve over time. Beneficial mutations result in species survival.