Learning outcomes (Chapters 25, 5, 23, 24, 27)

Summarize the experiments that enabled scientists to determine that DNA made up the genetic material

James Watson and Francis Crick worked out the 3-dimensional structure of DNA, based on work by Rosalind Franklin

Describe the structure of the DNA molecule

Two strands make up a double helix

• strands are held together by hydrogen bonding

  • complementary base pairing

    • adenine (A) + thymine (T) (apples and trees)

    • guanine (G) + cytosine (C) (garage and cars)

Explain why DNA replication is called semiconservative

One strand is new, one is old

Summarize the events that occur during the process of DNA replication

1. strands start hydrogen bonded

2. DNA Helicase unwinds/unzips the double-stranded DNA

3. new strands built complementary base paring of nucleotides by DNA polymerase

4. DNA Ligase seals any breaks in sugar-phosphate backbone

5. the 2 double helix molecules are identical to each other and to the original DNA molecule

Describe the roles of RNA molecules in gene expression

• Messenger RNA (mRNA): carries genetic info from DNA to ribosomes

• Transfer RNA (tRNA): transports amino acids to ribosomes

• Ribosomal RNA (rRNA): forms structural and core of ribosomes

Summarize the sequence of events that occur during gene expression

Transcription: (copy)

• In the nucleus

• Part of DNA serves as a template for mRNA formation

  • A gene (sequence of DNA)

Translation: (new language)

• Takes place in cytoplasm

• Sequence of mRNA determines the sequence of amino acids in a polypeptide

• tRNA assists by bringing amino acids to the ribosome

Determine the sequence of amino acids in a polypeptide, given the messenger RNA sequence

Start codon: AUG

Stop codons: UAA, UAG, UGA

Describe the molecules necessary for translation

Codons (mRNA) base pair with anticodons (tRNA) carrying specific amino acids

• mRNA

• tRNA

• rRNA

Describe the steps of the process of translation

• Initiation

  • Initiation factors assemble ribosome components

    • Small ribosomal subunit, mRNA, initiator tRNA, and the large ribosomal  subunit

  • The initiator tRNA attaches to the start codon (AUG)

  • The ribosome has 3 binding sites for tRNA

  • P (peptide) site, A (amino acid) site, and E (exit) site

• Elongation

  • A tRNA with attached peptide is at the P site, and a tRNA carrying the next amino acid is arriving at the A site

  • Once the next tRNA is in place at the A site, the peptide chain will be transferred to this tRNA

  • Translocation- mRNA shifts one codon, and the peptide-bearing tRNA is now at the ribosome P site

  • “Spent” tRNA exits, new codon is at the A site and ready for next complementary tRNA

• Termination 

  • New protein, rRNA, tRNA, and mRNA separate

  • Occurs at a stop codon

  • Last tRNA and polypeptide dissociate from one another

  • The ribosome dissociates into two subunits

Summarize the causes of gene mutations

• Errors in replication

  • DNA replication errors are a rare mutation source

• Mutagens

  • Environmental influences can cause mutations

    • Radiation, x-rays, UV radiation, certain chemicals

• Transposons - jumping genes

  • Specific DNA sequences that move within and between chromosomes

• Viruses - insert their DNA into host chromosomes

Describe the effect gene mutations can have on cells

• Point mutations: change in a single DNA nucleotide

• Substitution:

  • May change a specific amino acid

  • May have no effect - silent mutation

  • May produce an abnormal protein

    • Sickle cell due to abnormal globin protein

  • May produce an incomplete protein

• Frameshift mutations

  • One or more nucleotides are either inserted (insertion) or deleted (deletion) from DNA

  • The result can be a completely new sequence of codons and a nonfunctional protein

Describe why cancer is a failure of genetic control

Mutations disrupt the genes that regulate the cell cycle, which can lead to uncontrolled cell division and tumor formation

Describe the characteristics of cancer cells

• genetically unstable

• do not regulate cell cycle

• can escape signals for cell death

• can survive and proliferate elsewhere in the body

Describe the stages of the cell cycle and what happens in each stage. 

Interphase- divided into 3 stages

• G1: growth and acquire material for DNA synthesis

  • Checkpoint - if DNA is damaged then apoptosis

  • G0 - occurs in some cells, such as nerve and muscle (which do not go on to reproduce)

• S: each chromosome consists of one DNA molecule - chromatid

  • after DNA replication, each chromosome consists of two sister chromatids

• G2: the cell synthesizes proteins for cell division

  • Checkpoint - of DNA is damaged then apoptosis

Miotic Stage - division of the nucleus

• prophase

  • DNA condenses into chromosomes

  • miotic spindle begins to form

• prometaphase

  • nuclear envelope breaks down

  • tips of spindle microtubules attach to kinetochores on chromosomes

    • kinetochores - groups of motor proteins that can pull the chromosome spindle fiber

• metaphase

  • chromosomes aligned in the center of cell, forming metaphase plate

• anaphase

  • centromeres of each sister chromatid separate

  • kinetochores drag sister chromosomes toward opposite poles using motor proteins

  • spindle shortens

• telophase

  • spindle fibers reduce

  • nuclear envelope reforms

  • chromosomes uncoil and lengthen

• cytokinesis

  • cytoplasm divides into 2 separate cells

Describe the reasons for and process of apoptosis.

• occurs during development to remove unwanted tissue

• decreases number of cells

distinguish between internal and external controls of cell cycle

Internal

• inside the cell

• check whether the cell is ready to move to the next stage of the cell cycle

External

• outside the cell

• signals from other cells or the environment tell when to grow or divide

describe the checkpoints of the cell cycle

• G1: growth and acquire material for DNA synthesis

  • Checkpoint - if DNA is damaged then apoptosis

• G2: the cell synthesizes proteins for cell division

  • Checkpoint - of DNA is damaged then apoptosis

differentiate between proto-oncogenes and tumor suppressor genes in their regulation of the cell cycle

proto-oncogenes (gas)

• encourage cell growth and division

• helps cells move through the cell cycle when needed

• when mutated/overactive, they can become oncogenes, causing cells to divide uncontrollably

tumor suppressor genes (brakes)

• slow down/stop cell division

• can repair DNA damage/trigger cell death when damage is too severe

• when these genes stop working, cells make divide uncontrollably

describe how oncogenes and mutated tumor suppressor genes work

oncogenes (gas pedal on)

• oncogenes are mutated/overactive version of proto-oncogenes

• send signals telling cells to grow and divide too much

• even when a cell doesn’t need to divide, oncogenes may keep telling it to multiply

mutated tumor suppressor genes (broken brakes)

• when mutated, they stop working properly (usually slow down/stop cell cycle)

• damaged cells can continue to divide instead of being stopped

explain the role of mitosis in the cell cycle

divides the nucleus

explain how mitosis maintains the chromosome number from the mother cell to the daughter cells

makes sure that each daughter cell receives an identical set of chromosomes from the mother cell

list and summarize the events of the phases of mitosis and cytokinesis

• prophase

  • DNA condenses into chromosomes

  • miotic spindle begins to form

• prometaphase

  • nuclear envelope breaks down

  • tips of spindle microtubules attach to kinetochores on chromosomes

    • kinetochores - groups of motor proteins that can pull the chromosome spindle fiber

• metaphase

  • chromosomes aligned in the center of cell, forming metaphase plate

• anaphase

  • centromeres of each sister chromatid separate

  • kinetochores drag sister chromosomes toward opposite poles using motor proteins

  • spindle shortens

• telophase

  • spindle fibers reduce

  • nuclear envelope reforms

  • chromosomes uncoil and lengthen

• cytokinesis

  • cytoplasm divides into 2 separate cells

compare and contrast mitosis and cytokinesis in plant and animal cells

• Cytokinesis in Animal Cells

  • Cleavage furrow forms between daughter nuclei

  • Contractile ring contracts, deepening the furrow

  • Process continues until separation is complete

• Cytokinesis is Plant Cells

  • A new cell wall created

    • A flattened, small disk appears between daughter cells

    • A cell plate forms

    • Vesicles release molecules to build new cell walls

    • Vesicle membranes complete plasma membranes

name the phase of mitosis a cell is in from a diagram or micrograph

ex: prophase, metaphase, anaphase, telophase, cytokinesis

describe the purpose of meiosis

• Reduces chromosome number in half

• Provides offspring with different combination of traits from that of either parent

  • Genetic variation

• Begins with one diploid parental cell

• Ends with four haploid daughter cells

explain what is meant by the term homologous chromosomes

a pair of chromosomes that have the same size, shape, and genes in the same locations, with one chromosome inherited from each parent

describe the important events of meiosis that cause the halving of the chromosome number in daughter cells

• Meiosis I

  • Homologues line up side by side at equator (synapsis)

  • When homologous pairs separate, each daughter cell receives one member of the pair

  • The cells are now haploid

    • Prophase I

      • Homologous chromosomes come together as pairs by synapsis

      • Each pair, with 4 chromatids, called tetrad

      • Nonsister chromatids exchange genetic material by crossing over

    • Metaphase I

      • Tetrads align at cell equator

    • Anaphase I

      • Homologous pairs separate and move toward opposite poles of the cell

    • Independent assortment occurs when these homologous separate from each other during anaphase I

    • FIRST DIVISION

    • Metaphase and Anaphase I

      • Independent assortment - gametes get different combinations of maternal and paternal chromosomes

      • In humans, with 23 pairs of chromosomes, the number of possible combinations is 2^23, or 8,388,608

      • This value does not include genetic recombination due to crossing-over

    • Telophase I

      • Daughter cells have one chromosome from each homologous pair

• Meiosis II

  • Sister chromatids migrate to opposite poles to become individual chromosomes

  • Each of the four daughter cells produced has the haploid chromosome number

  • SECOND DIVISION

  • Phases of meiosis II

    • Prophase II

      • Cells have one chromosome from each homologous pair

      • Each duplicated chromatid attaches to spindle

    • Metaphase II

      • Sister chromatids line up at metaphase plate

    • Anaphase II

      • Sister chromatids separate and become daughter chromosomes that migrate toward the spindles

    • Telophase II

      • Spindle disappears

      • The nuclear envelope re-forms

      • Cytokinesis occurs

describe the important events of meiosis that cause the genetic diversity of gamete cells

crossing over - swapping DNA

independent assortment - random chromosome combinations

outline the major events that occur during meiosis I and II, focusing on activities of chromosomes

Meiosis I

• Homologues line up side by side at equator (synapsis)

• When homologous pairs separate, each daughter cell receives one member of the pair

• The cells are now haploid

Meiosis II

• Sister chromatids migrate to opposite poles to become individual chromosomes

• Each of the four daughter cells produced has the haploid chromosome number

compare and contrast the processes of meiosis and mitosis

• Meiosis occurs only at certain times

  • After the reproductive organs mature to produce gametes

• Mitosis takes place almost continuously in all tissues as part of growth and repair

describe the human life cycle in terms of haploid and diploid cells

diploid (2n): cells have two sets of chromosomes, one set from each parent (humans have 46 chromosomes)

haploid (n): cells have one set of chromosomes (human sperm & egg cells have 23 chromosomes)

explain the process of gamete production in male and female humans

humans produce gametes (sex cells) through gametogenesis. This happens through meiosis and produces haploid cells with 23 chromosomes

spermatogenesis: production of sperm in males

• in testes

• produce sperm

oogenesis: production of eggs in females

• in ovaries

• produces eggs

Describe how Mendel’s law of segregation and law of independent assortment are related to the movements of chromosomes during gamete formation. 

LoS: homologous chromosomes separate, so alleles separate

LoIA: homologous pairs line up randomly, creating different combinations of chromosomes

Define the term allele and explain what it means for an allele to be dominant or recessive. 

Allele: determine variations in inherited traits

• dominant allele: expressed whenever at least one copy is present

  • represented by a capital letter

  • only one copy is needed for the trait to show

• recessive allele: expressed only when two copies are present

  • represented by a lowercase letter

  • two copies are needed for the trait to show

contrast the terms genotype and phenotype

genotype

• an organism’s genetic makeup

• allele combination

phenotype

• observable traits

• what the trait looks like

predict the outcome ratios and probabilities for genotypes and phenotypes of problems based on Mendelian patterns of inheritance

Bb X Bb

Four possible combinations:

BB, Bb, Bb, bb

genotype ratio - 1:2:1

phenotype ratio - 3:1

Genotype: BB

probability: 25%

Genotype: Bb

probability: 50%

Genotype: bb

probability: 25%

use a pedigree to determine if a trait is autosomal dominant or autosomal recessive

look at slides

describe the mode of inheritance, symptoms, and physiological actions of the genetic disorder Tay-Sachs, cystic fibrosis, sickle cell disease, and Huntington’s disease

Tay-Sachs: autosomal recessive, fat buildup in nerve cells

Cystic Fibrosis: autosomal recessive, thick, sticky mucus

Sickle Cell: autosomal recessive, abnormally shaped red blood cells

Huntington’s: autosomal dominant, damage to brain nerve cells

explain how the phenotypes for incompletely dominant and codominant traits differ from dominant/recessive traits

describe polygenic inheritance and the kinds of traits that might be polygenic

explain the special characteristics of inheritance of alleles of the ABO blood group

describe ways a scientist might determine if a trait is strongly affected by the environment