Genetics and Protein Synthesis EOC Crash Course

Item 1: Describe the basic structure of the nucleic acids – DNA and RNA Nucleic acids are composed of nucleotides Nitrogen base + sugar + phosphate

Item 2: State the 3 structural differences between DNA and RNA RNA contains ribose; DNA contains deoxyribose DNA contains adenine (A), thymine (T), guanine (G), and cytosine (C) ; RNA contains A, G, C, and uracil (U) DNA is double stranded (double helix); RNA is single stranded (single helix)

Item 3: Summarize the relationship between DNA, genes, and chromosomes Chromosome – structure in the nucleus consisting of one long thread of DNA that is tightly coiled around special proteins called histones DNA – molecule composed of nucleotides, providing the blueprint for the making of proteins Gene – segment of DNA with the genetic code for making one protein Chromosomes are made of DNA (and protein), in which small segments code for the amino acid sequence of a protein

Item 4: Summarize DNA Replication

Enzyme unwinds DNA Enzymes breaks hydrogen bonds holding pairs bases together Another enzyme bonds new DNA nucleotides to each strand Each identical DNA molecule has ½ the original strand and ½ of a new strand This is called the semi-conservative model

Item 5: Summarize Protein Synthesis Consists of two steps: Transcription: DNA to mRNA Translation: mRNA to polypeptide (protein)

Transcription The two complementary strands of DNA separate by breaking the hydrogen bonds between paired bases An enzyme bonds RNA nucleotides to one DNA strand T bonds to G and A (on DNA) bonds to U (on RNA)

Translation Translation begins with mRNA attaching to a ribosome The first codon on mRNA is read (usually AUG) and the tRNA with the codon’s corresponding anticodon brings an amino acid to the ribosome A second codon is read and a second tRNA, also carrying the corresponding amino acid, attaches to the codon

The two amino acids bond together The first tRNA breaks away from the mRNA and the mRNA slides down to read the next codon This continues until one of the stop codons is reached The long chain of amino acids is a polypeptide

Amino acids bond by making peptide bonds

The Genetic Code

Item 6: Summarize steps of meiosis Meiosis is very similar to mitosis, except in meiosis, the daughter cells divide twice instead of once crossing over occurs during prophase I (mixes up genes) chromatids don’t separate until anaphase II all 4 daughter cells are genetically different, cells are haploid (1 chromosome per pair)

Stages of Meiosis: Meiosis I Prophase I: The chromosomes condense, and the nuclear envelope breaks down. crossing-over occurs Metaphase I: Pairs of homologous chromosomes move to the equator of the cell. Anaphase I: Homologous chromosomes move to the opposite poles of the cell Telophase I and Cytokinesis: Chromosomes gather at the poles of the cells. the cytoplasm divides.

Stages of Meiosis: Meiosis II Prophase II: A new spindle forms around the chromosomes. Metaphase II: Chromosomes line up at the equator. Anaphase II: Centromeres divides. Chromatids move to the opposite poles of the cells. Telophase II and Cytokinesis: A nuclear envelope forms around each set of chromosomes. the cytoplasm divides.

Item 7: Summarize Mendel’s Genetics Principles Principle of Dominant and Recessive – some genes can hide or mask others Law of Segregation – Mendel’s genetics principle that states that genes in pairs separate during gamete formation and gene pairs are reformed during fertilization Law of Independent Assortment – genes are inherited separately and that creates a variety in a population

Item 8: Complete Punnett Square to determine various modes of inheritance Monohybrid crosses – Punnett squares showing one trait at a time Genotype – the alleles (represented by a letter) Phenotype – the trait seen (physical description)

Sex-linked – genes found on the sex chromosomes In humans, females have 2 X chromosomes and males have 1 X chromosome and 1 Y Most sex-lined traits are on the X chromosome Example: hemophilia and Duchenne muscular dystrophy

Sex-Linked Punnett Square Example Allele for the trait is a exponent on the X chromosome Females have to have 2 h’s to inherit the recessive trait Males only need 1 h to inherit the sex-linked trait

Multiple Alleles Punnett Square Multiple Alleles – more than 2 alleles (forms of a gene) Example: blood types in humans; there are 3 alleles instead of 2; A gene, B gene, and O gene

Codominance Punnett Squares Codominance – 2 different alleles that are both dominant, so in a heterozygous gene pair, both traits show up Example: A and B genes in human blood type; if a person is AB genotype, they make both A and B proteins and have blood type AB

Incomplete Dominance Punnett Squares Incomplete Dominance – heterozygous genotype gives a different phenotype Example: red and white genes in Japanese four o’clocks; a red gene paired with a white gene makes a pink flower

Polygenic Traits – traits controlled by more than one pair of genes; example: human skin color and human height

Dihybrid Crosses – Punnett squares showing 2 traits; 16 square Punnett squares

RrYy Dihybrid Cross Advice On a dihybrid cross, if both parents are doubly heterozygous, the ratio in the offspring is 9:3:3:1 When determine parents’ potential gametes use the FOIL method First of each allele Outside alleles Inside alleles Last of each allele RrYy

Item 9: Explain Gene Linkage Discovered after Mendel; states that if genes are on the same chromosome and located close together, they are often inherited together Example: red hair and freckles in people Seems to violate Mendel’s independent principle, but as long as genes are on different chromosomes or found far apart on the same chromosome, his principle holds true

Item 10: Give examples of both chromosomal and gene mutations Chromosomal mutations affect a large part of a chromosome and therefore all of the genes on that section of the chromosome Gene mutations only affect one gene and therefore, one protein

Types of Mutations Deletion mutations – deletion of a section of chromosome or one small section of a gene Example: cystic fibrosis Substitution mutations – one base gets substituted for another one Example: in sickle cell

Nondisjunction mutations – chromatids or homologs fail to separate during meiosis; example: Down’s syndrome is caused from an extra 21st chromosome Point mutation – affects one amino acid Frameshift – changes a whole sequence of amino acids

Item 11: Explain the difference between somatic and germ cell mutations Somatic mutations take place in cells of the body (skin, muscle, etc.) and are not passed on to offspring germ cell mutations occur in sex cells and are passed from parent to offspring

Item 12: Identify Common Mutations Sickle cell anemia – causes abnormally shaped red blood cells; autosomal recessive Tay-Sachs – mutation in a gene for an enzyme that functions in the breakdown of a protein in neurons; autosomal recessive Cystic fibrosis – mutation in a Cl- transport protein; autosomal recessive Hemophilia – mutation in gene for blood clotting; sex-linked

More Disorders Caused by Disorders Huntington’s – progressive nervous deterioration; symptoms don’t occur until middle age; autosomal dominant Albinism – mutated gene for pigments; white hair; white skin; usually pink eyes

Mutations caused by nondisjunction Down’s – extra 21st chromosome Klinefelter’s – extra X chromosome; males; XXY Turner’s – missing X chromosome; females; XO

Interpret pedigrees to determine how a trait is inherited in a family

How is this trait inherited?

How is this trait inherited?

Questions?