Unit 7 Bio

Key Terms

Transformation-When a cell takes in external DNA, causing its traits to change

Okazaki Fragments-Short pieces of DNA that are made on the lagging strand during DNA replication

Leading Strand–The strand that is synthesized continuously as the DNA polymerase moves in that same direction

Lagging Strand-The strand that is synthesized discontinuously, and DNA is built in short segments

Nucleotides-Monomer of DNA and RNA

Amino Acids-Monomer of proteins 

Antiparallel-How two strands of DNA run in opposite directions

Purine-double ringed nitrogenous base

Pyrimidine-single ringed nitrogenous bases

Telomere Erosion-The gradual shortening of the telomere, which are protective caps at the end of each chromosome

  • Promotes aging by triggering DNA damage response which stops cells from dividing, causing tissues to lose functions and become unable to repair themselves

Transcription-The synthesis of RNA using a DNA template

Translation-The synthesis of a polypeptide using the genetic info encoded in a mRNA molecule. 

Central Dogma of Genetics-The flow of genetic information from DNA to RNA to proteins

Template strand-The strand used to produce an mRNA transcript

Start Codon-The three nucleotides that signal the beginning of translation (typically AUG)

5’ cap-Modified form of a guanine nucleotide that protects the mRNA and helps ribosomes attach (Occurs at the 5’ end during mRNA editing)

Poly-A-Tail-About 50-250 adenine nucleotides are added. It protects the mRNA and helps it leave the nucleus (Occurs at the 3’ end during mRNA editing)

Mitosis

  • Mitosis is the process of which the nucleus divides, which is essential for growth and repair

    • Makes cells identical to the parent cell

    • Makes all body cells (DOES NOT MAKE SPERM OR EGG CELLS)

    • Product of mitosis has the same amount of chromosomes as the parent cell (diploid)

  • Phases of mitosis

    • Interphase

    • M-phase

  • Interphase

    • G1-The first stage of interphase where the cell grows, makes proteins and organelles, and maintains cellular functions

    • S-The second stage of interphase where DNA is replicated, so each chromosome will have two sister chromatids joined by the centromere

    • G2-The last stage where the cell continues to grow, produces proteins needed for mitosis, and repair mistakes

    • G0-Resting phase where the cells still carry out their functions, but they do not prepare for mitosis.

      • Some cells are forever in this phase. Example-Nerve cell

      • Some cells move here when they do not receive the go-ahead signal to continue dividing 

  • Prophase

    • Chromosomes begin to condense 

    • Asters and spindles begin to form

    •  Nuclear envelope disappears

  • Metaphase

    • Chromosomes line up at the middle of the cell in a single file vertical line

  • Anaphase

    • Sister chromatids are pulled apart at the centromere and move to opposite sides of the cell

    • The spindle fibers attached to the chromatids help move the chromatids to opposite poles of the cell

  • Telophase

    • The chromosomes are at opposite ends of the cell and the nuclear envelope forms around the chromosomes

  • Cytokinesis

    • The cytoplasm is split, dividing the cell into 2

  • Animal Cytokinesis

    • Forms a cleavage furrow

  • Plant Cytokinesis

    • Forms a cell plate that turns into a cell wall

Meiosis 

  • Meiosis makes sex cells, gametes, (sperm and egg cells) which contribute to genetic variety

    • Gametes have half the amount of chromosomes of their parent cell (they are haploids) 

    • Meiosis is a type of reduction division as it goes from 46 chromosomes to 23 chromosomes (HUMAN EXAMPLE)

    • In meiosis PMAT occurs twice, once in meiosis one, and once in meiosis two

  • Meiosis 1

    • Prophase 1

      • Chromosomes condense and line up with their homologous pairs 

      • Crossing over occurs after homologous chromosomes are paired, which is the physical exchange of chromosomal material between homologous chromosomes.

        • This results in a new combination of alleles resulting in genetic variation

      • Crossing over must occur between nonsister chromatids because sister chromatids have the same DNA

      • Recombination also occurs in prophase 1 and is the result of crossing over which increases genetic variation

  • Metaphase 1

    • Chromosomes are lined up in their homologous pairs at the middle of the cell (NOT SINGLE FILE LINE)

  • Anaphase 1

    • Chromosomes are being pulled apart by spindle fibers 

  • Telophase 1

    • Results in 2 newly formed nuclei and 2 new cells

  • Cytokinesis 1

    • The cytoplasm splits

  • Meiosis 2

    • Prophase 2

      • Chromosomes condense and spindles begin to form  

  • Metaphase 2

    • Chromosomes are lined up in a single file line in the middle (NO PAIRS)

  • Anaphase 2

    • Chromatids are being pulled away from each other by the spindle fibers

  • Telophase 2

    • Nuclei forms and the 2 cells will each have 2 nuclei inside them (4 nuclei in total)

  • Cytokinesis 2

    • The cytoplasm of each cell divides, resulting in a product of 4 cells

Eukaryotic vs. prokaryotic cell division

  • Prokaryotic cells

    • DNA Form-Single circular chromosome

    • No nucleus

    • Process of binary fission

    • Simple, fast

    • No spindle fibers

    • Two identical daughter cells

  • Eukaryotic cells

    • DNA Form-Multiple linear chromosomes

    • Nucleus

    • Mitosis or meiosis

    • Complex, slower

    • Spindle fibers

    • Identical (mitosis) or different (meiosis)

Mendelian Genetics

  • A branch of genetics based on the principles of Gregor Mendel’s study of pea plants

  • He observed the pea plants…

    • Stem height- Tall vs. Short

    • Pod Shape- Round vs. Wrinkled

    • Flower Color-Purple vs. White

Law of Segregation

  • Every organism has two alleles for a trait, but during the process of meiosis, these two alleles separate, resulting in 1 allele per gamete. 

  • Then the two gametes create a zygote during fertilization that has two alleles per trait–one from mom and one from dad

Law of Dominance

  • All traits can only have two alleles and one is dominant and the other is recessive

  • The dominant allele will mask the expression of the recessive allele, resulting in the dominant allele being expressed as the organism’s phenotype

Law of Independent Assortment

  • States that different traits are passed down from parent to offspring independently of each other.

    • For example, this law believes that there is no connection between the eye color and person has and the skin color that person has

Dominant vs. Recessive Alleles

  • Dominant alleles are represented by a capital letter. Example-G

    • It only takes one dominant allele for the trait to be expressed, so the combination of alleles can be either heterozygous or homozygous. 

    • For example, for the dominant trait to be expressed, the combination can be GG (Homozygous) or Gg (Heterozygous)

      • Just because a trait is dominant does not mean it is more common; it just means the allele masks the recessive allele when both are present

  • Recessive alleles are represented by lowercase letters. Example-g

    • In order for a recessive allele to be expressed, there must be a homozygous combination of the recessive allele 

    • Example- gg (homozygous)

Punnett Squares

  • A Punnett squares are based on Mendel’s principles of genetics and is used to predict the genotype and phenotype of an offspring

  • PUNNETT SQUARES ARE A PREDICTION, AND NOT DEFINITIVE

    • A monohybrid cross focuses on one trait being expressed 

Key Figures of Unit 7

  • Alfred Hershey + Martha Chase

    • Proved DNA influences inheritance

  • Erwin Chargaff

    • Discovered base pairing rules- adenine with thymine and cytosine with guanine

  • Rosalind Franklin

    • Discovered that DNA had a helical structure using X-ray crystallization 

  • Watson + Crick

    • The fathers of DNA discovered the double helix shape of DNA

DNA 

  • DNA- Deoxyribonucleic Acid 

    • DNA is made of a phosphate group, a 5 carbon sugar, and a nitrogenous base (adenine, thymine, guanine, and cytosine)

    • The phosphate and sugar form a sugar-phosphate backbone

    • The nitrogenous bases are like the rungs of a ladder

    • Found is ALL organisms

    • Made of deoxyribose sugar

  • Nitrogenous bases

    • Base pairings

      • Adenine and thymine pair up together

      • Cytosine and guanine pair up together 

    • Purines are nitrogenous bases that have a double ring structure

      • Adenine and guanine 

    • Pyrimidines are nitrogenous bases that have a single ring structure

      • Thymine, cytosine, uracil (RNA)

    • This structure explains why adenine and thymine pair together and why cytosine and guanine pair together. As purine + pyrimidine keeps the width of DNA consistent and stable

  • DNA Structure

    • There is a 5’ end and a 3’ end on the DNA strands 

    • The DNA strands run antiparallel of each other as one strand runs from the 5’ to 3’ direction and the corresponding strand runs from the 3’ to 5’ direction

    • DNA is double strands and the two strands twist around each other forming a double helix structure

DNA Structure

Antiparallel strands

RNA

  • RNA has the same structure as DNA, but instead of deoxyribose sugar RNA has ribose sugar

  • RNA is single stranded

  • RNA is found in ALL organisms 

  • Instead of a thymine base, adenine pairs with URACIL 

  • RNA types

    • mRNA-Carries messages based off the DNA out of the nucleus and into the cytoplasm

    • rRNA-The type of RNA that combines with proteins to make ribosomes

    • tRNA–Reads the genetic code on mRNA and delivers the corresponding amino acid to a ribosome

      • When multiple amino acids are put together it creates a polypeptide chain

DNA Replication (In eukaryotic cells)

  • DNA replication occurs during S phase of the cell cycle 

  • Helpers involved in DNA replication (in order)

  1. Helicase–Unzips the two strands of DNA by breaking apart the hydrogen bonds, creating a replication fork

  2. Single-stranded binding proteins (NOT AN ENZYME)- Holds the DNA strands apart

  3. Primase–Adds a small piece of RNA onto the nucleotide bases 

  4. DNA Polymerase  lll –Binds the the primer and adds DNA nucleotides making a new DNA strand

  5. Topoisomerase-Prevents DNA from tangling during DNA replication

  6. Ligase–Seals the gaps between the Okazaki fragments and forms the final continuous sugar-phosphate backbone

  7. DNA Polymerase l-Removes RNA primer and replaces it with DNA

  • Steps of DNA replication

    1. Helicase unzips the double strand of DNA, creating a replication bubble

    2. Primase adds a small piece of RNA (primer) on both strands

    3. DNA polymerase builds a new strand, but it only does so in a 5’ to 3’ direction

      • This results in a leading strand, the 5’-3’ strand, which is made continuously

      • This also creates a lagging strand, the 3’-5’ strand,  which is made of Okazaki fragments (There are gaps between the fragments because DNA polymerase can only move from 5’-3’)

    4. DNA polymerase removes the RNA fragments and replaces them with DNA

    5. Finally ligase seals the fragments of DNA together (Think like glue)

Protein Synthesis

  • Genes code for protein which actual perform the trait

  • DNA DOES NOT CARRY OUT THE PHYSICAL TRAIT, PROTEINS DO

  • Steps of protein synthesis

    • Transcriptions (Starts with DNA, results in mRNA)

      1. The DNA in the nucleus is used as a template to make mRNA

        • RNA polymerase attaches RNA nucleotides to the matching bases on the DNA strand 

        • These RNA nucleotides link together to form mRNA 

      2. The finished mRNA leaves the nucleus, enters the cytoplasm, and attaches to a ribosome

    • Translation (Starts with mRNA, results in a polypeptide chain)

      1. tRNA molecules in the cytoplasm pick up and carry specific amino acid to a ribosome (THE tRNA WILL ALWAYS PICK UP THE SAME AMINO ACID)

      2. The codons on the mRNA determine which amino acid is added

      3. tRNA reads the mRNA in groups of three bases (codons)

      4. Each tRNA has an anticodon that pairs with the matching mRNA codon

      5. When the tRNA binds to the mRNA, the amino acid it carries is added to the growing chain

      6. As this repeats over and over, a full polypeptide chain is built

Mutations

  • A  mutation is a change in the DNA sequence 

    • Types of mutations 

    • Point mutation–When a single nucleotide base is replaced with another

    • Frameshift mutation–When nucleotides are either inserted or deleted from the nucleotide sequence 

      • Creates an issue because the nucleotides will no longer be grouped in three, which changes the number of codons and causes extra or missing nucleotides to be left out

    • Silent mutation-When the nucleotide sequence codes for the same amino acid

    • Nonsense mutation-When the nucleotide sequence codes for a STOP instead of an amino acid

    • Missense mutation-When the nucleotide sequence codes for a completely different amino acid

    • Chromosomal Inversion-When an entire section of DNA is reversed

Genetic Disorders

  • Nondisjunction-The failure of chromosomes to separate during anaphase

  • Karyotype-A graph of all the chromosome pairs, so it can be easily examined

  • Example-Tay-Sachs Disease which is a hereditary condition leading to many issues caused by enzyme deficiencies 

  • Pedigrees help analyze the passing down of traits within a certain family

Genetic Engineering

  • Gene Therapy-A technique aimed at correcting defective genes responsible for diseases

  • Genetic engineering-The human manipulation of a cell’s genetic material through recombinant DNA technologies

    • Recombinant DNA-DNA that's created by combining genetic material from different sources

    • Used in agriculture and medicine

  • Human Genome Project-Initiative aimed at mapping the entire gene sequence, facilitating the study of genetic diseases