Unit 3 - Molecular Biology & Genetics Flashcards
The Cell Cycle
Life cycle of body (SOMATIC) cells. Does not include gametes.
Organization of Genetic Material
All genetic info contained in DNA. Each cell’s nucleus contains chromosomes, each chromosomes is made up of DNA.
–> DNA is wrapped around HISTONE proteins.
–> Histone forms a bead like structure called CHROMATIN.
–> Chromatin forms loops and scaffolds which forms a condensed CHROMOSOME.
Homologous Choromosome
Contain the same genes (sections of DNA containing genetic info) at the same locations.
–> Similar in physical appearance; size, band patterns, same position of centromeres.
Alleles
Homologous chromosomes could contain different forms of the same gene.
–> Ex. one hc carries blue eyes while the other carries brown eyes.
Ploidy
If a cell contains unpaired chromosomes, they are HAPLOID (n).
–> If a cell contains pairs of homologous chromosomes (like humans), they are DIPLOID (2n).
–> Some organisms are polyploid which contains sets of more than 2 chromosomes. (3n = Triploid, 4n = Tetraploid, etc.)
Karyotype
Complete set of an individual’s chromosomes.
–> Normal Human Somatic Karyotype: 22 pairs of autosomes + 2 sex chromosomes.
Phases of Cell Cycle
1) Interphase
2) Cell Division
Interphase Stages
1) G1 Phase (Gap/Growth)
2) S Phase (Synthesis)
3) G2 Phase (Growth)
G1 Phase (Gap/Growth)
Replication of cellular organelles (NOT INCLUDING DNA) - Mitochondria, ribosomes, etc.
–> Cell grows in size.
–> Accumulates structures for DNA replication (S Phase).
S Phase (Synthesis)
DNA REPLICATION (Doubled)
–> In humans, single-stranded (unduplicated) chromosomes in somatic cell to form 46 double-stranded (duplicated) chromosomes.
–> These double-stranded chromosomes are made up of SISTER CHROMATIDS.
G2 Phase (Growth)
Replenishes energy to prepare for cell division.
–> The cell manufactures proteins and structures required for cell division.
What is Mitosis?
Division of DNA inside nucleus.
Mitosis Stages
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase
Prophase (Mitosis)
Chromatin condenses into chromosomes (double stranded, 2 sister chromatids held together by centromere).
–> Nuclear membrane and nucleolus breakdown.
–> Centrioles move to opposite ends of cell, spindle fibres form.
Metaphase (Mitosis)
Spindle fibers attach to centromere of each chromosome to equator of cell.
–> Each sister chromatid faces one end of the cell.
Anaphase (Mitosis)
Spindle fibers shorten, centromere splits, sister chromatids pulled apart to opposite ends of cell.
Telophase (Mitosis)
Begins when chromatids reach opposite poles of cell.
–> Chromosomes unwind into chromatin.
–> Nuclear membrane and nucleus reforms.
–> Spindle fibers breakdown.
Cytokenesis
Division of cytoplasm and organelles into 2 separate cells.
–> Forms 2 new DAUGHTER CELLS with the same genetic information as PARENT CELL.
ANIMALS: Indentation forms in cell membrane, cell is pinched in the middle form 2 daughter cells.
PLANTS: Cell plate forms in the middle of the cell, reinforced by cellulose for a new cell wall separating daughter cell.
Cancer
Uncontrolled cell division; Failure of regulatory mechanisms of cell division.
What is Meiosis?
Formation of gametes (egg and/or sperm).
Reduction Division
Daughter cells contain half of the number of chromosomes of parent cell (2n=46 –> n=23).
Recombination
Daughter cells are NOT genetically identical to parent cell, offspring organisms are genetically identical to either parent organism.
Phases of Meiosis
1) Interphase
2) Meiosis I
3) Meiosis II
Interphase (Meiosis)
Germ cells (cells which produces gametes) goes through growth and synthesis. Basically not much different from the interphase in mitosis.
Meiosis I
Homologous chromosomes pair up and separate from each other.
Meiosis II
Sister chromatids separate from each other (similar to mitosis).
–> No interphase (no DNA replication between I and II).
–> End with four daughter cells, haploid, single stranded.
n(ds) –> n (ss)
Prophase I *
Nuclear membrane disappears, spindle fibers form, etc.
–> In the nucleus, homologous pairs come together and CROSSOVER, exchanging genetic info.
–> This process is called SYNAPSIS.
–> Crossover occurs between non-sister chromatids.
–> Increases genetic variation.
–>Crossover is random, may not happen in all chromosomes.
Metaphase I
Spindle fibers guide homologous pairs to line up at equator.
Anaphase I
Spindle fibers shorten, homologous chromosomes separate.
Telophase I
Nuclear membrane forms, spindle fibers disappears, etc. Results in two haploid cells 2n(ds) –> n (ds).
Crossover*
During Prophase
Independent Assortment *
During METAPHASE I
Nondisjunction
Homologous chromosomes or chromatids don’t separate properly , happens during anaphase (I or II).
Anaphase I: both homologous chromosomes go to one end (4 gametes affected).
Anaphase II: both sister chromatids go to one end (2 gametes affected).
Can result in TRISOMY (3 homologous chromosomes) or MONOSOMY ( 1 homologous).
Spermatogenesis Stages *
The creation of sperm from a diploid germ cell called a SPERMATOGONIUM.
Spermatogonium then undergoes MITOSIS to produce PRIMARY SPERMATOCYTE during puberty.
Primary undergoes MEIOSIS I to produce SECONDARY SPERMATOCYTE which goes under MEIOSIS II to become 4 SPERMATIDS (sperm) in testicles.
Oogenesis Stages *
Starts with diploid germ cell: OOGONIUM.
Oogonium undergoes mitosis to become PRIMARY OOCYTE (diploid).
During puberty, primary undergoes meiosis I to become SECONDARY OOCYTE (haploid). Due to unequal cytoplasmic distribution, 1st polar body is released which may or ma not go through division.
Meiosis II only occurs if egg is fertilized. When it does happen, secondary becomes OVUM. Second polar body is released.
Oogenesis *
Egg at ovulation is considered secondary oocyte.
–> Oogenesis produces 1 ovum, not 4.
Twins
IDENTICAL: Same egg, same sperm. During cleavage, zygote splits into two.
FRATERNAL: 2 separate eggs and sperm. 2 eggs gets released during ovulation and both are fertilized by different sperms.
Sexual Reproduction
Uses gametes from different parents, which higher genetic variation.
Asexual Reproduction
When the offspring is identical to the parent (little to no genetic variation).
Thomas Hunt Morgan
Discovered that genes are located on chromosomes.
Rosalind Franklin
Contributed greatly to present day model of DNA. She used x-ray crystallography to produce images of DNA.
James Watson and Francis Crick
They used Franklin’s results to publish DNA structure. They discovered two important features about the structure of DNA:
1) DNA is a helix.
2) DNA contains repeating units
Structure of DNA
DNA: Deoxyribonucleic Acid
–> Unique because it can replicate itself.
–> Made up of a long chain of NUCLEOTIDES.
Contains: 2 strands of nucleotides, connected by H bonds on nitrogenous bases.
Nitrogen bases are found in the helix and the sugar-phosphate backbone is located outside.
4 Nitrogenous Bases
1) Adenine (A)
2) Guanine (G)
3) Cytosine (C)
4) Thymine (T)
Nucleotides
Made up of PHOSPHATE, SUGAR MOLECULE (Deoxyribose), and one of the four NITROGENOUS BASES.
Anti - Parallel
One strand runs to 5’ to 3’, the other runs to 3’ to 5’.
Complementary
Nitrogenous bases pair up.
Chargaff’s Rule *
A = T, G = C
–> 2 H bonds between A and T.
–> 3 H bonds between C and G.
–> These H bonds are the weakest in DNA molecule, can be broken to separate strands.
RNA
Ribonucleic Acid
–> The sugar is RIBOSE instead of deoxyribose.
–> URACIL (U) is paired with adenine instead of thymine (RNA doesn’t have T).
–> Single stranded but can sometimes fold on itself to to produce complementary base pairs.
Human Genome
Genome: All DNA carried in human cells, 46 chromosomes.
–> Each chromosome carries genes which contains genetic info.
–> Each chromosome contains sections of non-coding DNA.
DNA Replication
Considered SEMI-CONSERVATIVE because after replication, each DNA molecule contains one original parent strand and one new daughter strand.
–> Occurs in 5’ to 3’ direction.
–> Occurs in 3 stages: INITIATION, ELONGATION, TERMINATION.
Initiation
A protein called HELICASE binds to DNA, unwinds (“unzips”) helix, breaks H bonds.
–> Forming many replication bundle section of DNA which has been separated.
Elongation *
DNA POLYMERASE adds nucleotides complementary to parent stand in the 5’ to 3’ direction.
PRIMASE lays down a few bases of RNA primer which gives DNA polymerase a starting point.
ON LEADING STRAND: as helicase unwinds more DNA, DNA polymerase keeps adding nucleotides in the same direction.
ON LAGGING STRAND: DNA polymerase replicates away from replication fork.
Replication happens in segments called OKAZAKI FRAGMENTS.
–>LIGASE glues fragments together.
–> Another enzyme changes RNA to DNA.
Termination
New DNA molecules completed, enzymes detach and disassemble.
–> Multiple REPLICATION BUBBLES on DNA expand until they meet, forming 2 separate DNA molecules.
Replication Enzymes (DNA)
–> Helicase
–> Primase
–> DNA Polymerase
–> Ligase
Protein Synthesis
Genes Code for Proteins (ex. hemoglobin, melanin, insulin, etc.): sequences of nucleotides corresponds to sequence of amino acids that make a protein.
Expressing the Gene –> Protein is Produced.
Transcription
mRNA (messenger RNA) is transcribed to form a section of DNA.
–> mRNA is a complementary copy of a gene, takes DNA info out of the nucleus.
Translation
Sequence of mRNA is used to put amino acids together to make protein in the cytoplasm.
–> Amino acid are brought to ribosome by tRNA.
Genes from the mRNA are expressed as a polypeptide chain which occurs in the cytoplasm.
2 DNA Strands (Transcription) *
Info from DNA is transcribed into mRNA.
–> in a gene, there are 2 DNA strands:
1) TEMPLATE STRAND: only one strand that is transcribed.
2) NON-TEMPLATE/CODING STRAND: the other strand that does not get transcribed.
DNA is unwound and separated, RNA POLYMERASE binds at promoter region (start of gene) and lays down RNA nucleotides complementary to template strand.
–> mRNA produced is complementary to template strand, but equal to coding strand.
–> When RNA polymerase reaches end of gene, it detaches, new mRNA strand also detaches.
The Genetic Code
mRNA is read in groups of 3 nucleotides called CODON.
–> Ex. In RNA codon: AUC = Isoleucine (iso), GGC = Glycine (gly).
Characteristics of the Genetic Code *
1) Redundant
2) Unambiguous
3) Continuous
4) Universal
Redundant
More than one codon codes for the same Amino Acid. (Ex. CCU/CCC = Proline).
Unambiguous
Codons are exclusive. Each codon can only code for one amino acid.
Continuous
Codons are read without spaces or nucleotides in between, and cannot overlap.
Universal
Nearly all organism use the same genetic code (eg. CCU = proline in humans, insects, bacteria, etc.)
Translation *
Amino acid are brought together in the ribosome by tRNA.
–> Each tRNA contains an anticodon complementary to mRNA codon, and carries an amino acid corresponding to the mRNA codon.
–> First tRNA (carrying met/AUG) attaches to a site inside ribosome. (INITIATION)
–> As subsequent tRNAs arrive, all previous amino acids are passed to the new tRNA, forming a chain. (ELONGATION)
–> When a stop codon is reached, ribosome disassembles, amino acids detaches. (TERMINATION)
Mutations
A change or error/mistake in the genetic material which can be passed to daughter cells through cell divisions.
–> Caused by MUTAGENS: Physical, Chemical
Can occur spontaneously (mistakes made during DNA replication) or they can be induced (caused by physical or chemical mutagens).
Physical Mutagens
Physically changes structure of DNA molecules.
–> Ex. UV, x-rays
Chemical Mutagens
Changes nucleotide sequence ex. heavy metals.
–> Often CARCINOGENIC (causes cancer).
Somatic Cell Mutations
Can be passed from cell to cell but not organism to organism.
–> Key cause of cancer.
Germ Line/Gamete Mutations
Occurs in gametes, can be passed to offspring organism.
Point Mutation
A change in 1 or few nucleotides.
SUBSTITUTION: nucleotides A –> nucleotide B. May cause change in amino acid sequence but not always because of genetic code redundancy.
INSERTIONS & DELETIONS: cause frameshift. Affects ALL amino acids after the mutation points. (Can cause much more serious affects than substitution.)
Mitochondrial DNA (mtDNA)
Mitochondria and chloroplast have a separate set of DNA.
–> mtDNA is identical to maternal mtDNA which can be used to trace maternal ancestry.
Recombinant DNA
DNA contains genetic material from different sources (different species).
Restriction Enzymes
Recognizes specific DNA sequences, and cut at these sequenes, and create complementary sticky ends.
–> Another piece of DNA is cut with same restriction enzyme, creating the same sticky ends.
–> Ligase is used to glue the 2 pieces of DNA together, creating recombinant DNA.
DNA Fingerprinting
DNA is cut with restriction enzymes, put throught GEL ELECTROPHORESIS to separate cut pieces.
–> The pattern created by separated pieces is unique (except for identical twins).
–> Used for identifying victims/perpetrators of crime, or for paternity.
Gregor Mendel
Studied how traits are passed down through generations of pea plants.
–>He crossed the TRUE-BREEDING plants: plants that exhibit the same characteristics through generations.
Monohybrid Cross
Inheritance of one traits. Every organism has two copies of each gene, different forms are called ALLELES.
Dominant Allele
“Hides” the expression of the RECESSIVE ALLELE.
Genotype (Monohybrid)
Two letter combination of alleles for a trait. Uppercase is dominant, lowercase is recessive.
Phenotype
Which version of the organism will show.
Mendel’s First Law: Law of Segregation
Each individual has two copies of every trait but when gametes are formed, the copies segregate randomly and each gamete carries one copy of every trait.
Test Cross
If an individual shows the dominant phenotype, they could be hom, dom, or het. To find out, cross the unknown individual with a hom.rec.
Incomplete Dominance
Blend/mix which result is a lack of dominance for both traits.
Codominance
The traits lack dominance, but instead they are intermingled together.
Mendel’s Second Law: Independent Assortment
Two alleles for each gene segregates independently of alleles for other genes.
Epistatsis
Two genes interact with each other and affect each other’s expression. It is like a regular dihybrid cross, except phenotypic ratio may not be 9:3:3:1.
Thomas Hunt Morgan
Studied sex-lined traits in fruit flies.
Linked Genes
Found on the same chromosome. Distance between two genes is related to likelihood of separation during crossover. Closer is most likely to stay together, while far apart is likely to separate.
Chromosomes Mapping
Determining relative position of genes on a chromosome. Distance between genes is measured in map units (MU).
Pedigree
Shows how a trait is inherited through generations in a family.
1) Autosomal Dominant
2) Autosomal Recessive
3) X-Linked Dominant
4) X-Linked Recessive
Autosomal Dominant
Unaffected parents (hom.rec) cannot produce affected children. Affected parents (het) can produce unaffected children.
Autosomal Recessive
Unaffected parents can produce affected children. Affected parents cannot produce unaffected.
Can skip generations.
X-Linked Recessive
Affected mothers will always have affected sons.
X-Linked Dominant
Affected fathers will always have affected daughters.
