Molecular Genetics and Cell division

DNA

Deoxyribonucleic acid

Functions and location of DNA

-found in nucleus of all cells of all organisms

-codes for characteristics

-regulates production of proteins

-only molecule that can replicate itself

Rosalind Franklin

-took pictures of DNA using x-ray diffraction

-discovered the double helix

Erwin Chargaff

-noticed that % of A and T matched and % of C and G matched

Watson and Crick

-built a structural model of DNA

-double helix

-complementary base pairs

DNA backbone

alternating sugar and phosphate molecules

DNA “rungs”

Nitrogen bases

4 possible nitrogenous bases

Adenine, Thymine, Guanine and Cytosine

Antiparallel

the 2 strands run parallel to each other in opposite directions

DNA is read in ____ direction

3’→ 5’

DNA is built in ____ direction

5’→ 3'

3’

the 3rd carbon on Deoxyribose starting at N base

5’

the 5th carbon on Deoxyribose starting at N base

Semiconservative Model

DNA replication that results in 2 DNA molecules with 1 new strand and 1 original parent strand

Helicase function

unzips the 2 strands of parent DNA by breaking H bonds between the base pairs

RNA primer function

added so that DNA polymerase can attach

DNA polymerase functions

-attaches to the RNA primer and build the new complimentary strand (5’→ 3’)

-cuts out RNA primer later and replaces it with DNA

-proofreads at the end

Leading Strand

DNA polymerase follows Helicase and builds the new DNA strand in one continuous piece

Lagging Strand

-DNA polymerase has to build in opposite direction of Helicase

-slower

-short segments called Okazaki Fragments

Ligase funtion

-forms a bond where DNA Polymerase left a gap (when primer was removed)

Mutations

-missed errors in DNA replication

-a source of new gentic variation

Genome

all the DNA within an organism

RNA

-ribonucleic acid

-3 types

-single stranded

-Uracil base in place of Thymine

The Central Dogma

the flow of genetic information from DNA to RNA to proteins

Gene expression (protein synthesis)

transcription and translation

Transcription

-happens in the nucleus

-use the template DNA strand to write complimentary mRNA transcripts

Translation

-happens in Cytoplasm

-mRNA moves out of nucleus

-mRNA codons are read by the Ribosome to make a polypeptide chain which then folds into a protein

mRNA codons

-3 nucleotides that code for 1 amino acid in translation

-DNA triplet is complimentary

Initiator codon

AUG

Redundancy

each amino acid has more than one codon which protects against mutations

tRNA

-transfers the amino acid to the polypeptide chain

-has the anticodon

Somatic Mutations

-in body cells

-will not be passed on to offspring

Germ-line Mutations

-in sperm or egg

-will be carried by all cells in offspring

-will stay in family

Mitochondrial DNA

-passed on through mother (egg)

-close it is to another person, the closer related you are

Mitosis

the process that produces 2 new nuclei with the same number and kind of chromosomes as original

Chromosome

-structure that holds DNA strand and proteins

-made up of chromatin

-can be condensed or uncondensed

-can be duplicated or unduplicated

-count by counting centromeres

Centrioles

-cylindrical organelle

-located near the nucleus

-occur in pairs

-involved in the development of spindle fibers

Spindle fibers

-seperate chromosomes during mitosis and meosis

Interphase

-90% of the cell cycle\

-DNA replication

G1: cell grows

S: DNA duplicates

G2: more growth

Prophase

-chromatin condenses to form visible chromosomes

-centrioles move to opposite sides of cell

-spindle fibers form

-nuclear membrane and nucleolus disapear

Metaphase

-sister chromatids align in the middle (equitorial plate) with the help of spindle fibers

Anaphase

centromeres divide and sister chromatids seperate

Telophase

-chromosomes uncondense

-spindle fibers dissolve

-nuclear membrane beings to reform

Cytokinesis

-cell divides into 2 equal sized cells

-in animal cells a microtubule tightens around middle and pinches cell in half

-in plant cells a new cell is formed in the middle

Cancer

-when cells go through uncontrolled rapid cell growth

-speed through the cell cycle and become non-functioning mass of cells called a tumor

Cloning

producing a genetically identical organism

Identical twins

-originate from a single egg and sperm cell

-during mitosis, one cell breaks free from the cell cluster and develops into a seperate baby

Meiosis

-cell division that forms gametes (haploid cells)

-2 stages

Ploidy

number of sets of chromosomes in a cell

Haploid

-half the typical number of chromosomes (n)

-chromosomes are unpaired (not unduplicated)

Diploid

-2 sets

-typical number of chromosomes (2n)

Homologus chromosomes

chromosomes that have the same size, shape and genes

Somatic cells

-non-reproductive cells

-have a homologus pair of each type of chromosome,1 from mom, 1 from dad (diploid)

-divide by mitosis

Sex cells (gametes)

-haploid

-created by meiosis

-combine with another sex cell during fertilization to make a zygote (2n)

Prophase I

-chromatin condenses into chromosomes (duplicated)

-nuclear membrane dissapears

-synapsis of homologus chromosomes forming tetrads and result in crossing over

Metaphase I

-homologus pairs line up side by side on metaphase plate

Anaphase I

homologus chromosomes are pulled apart but sister chromatids stay together

Telophase I

-chromosomes decondense

-nuclear envelope forms temporarily

-cytokinesis then produces 2 haploid cells

Prophase II

-same as Prophase I except cells are now haploid and there is no crossing over

Metaphase II

-spindle fibers pull duplicated chromosomes to metaphase plate

Anaphase II

-centromeres seperate

-sister chromatids move to opposites poles

Telophase II

-chromosomes decondense into chromatin

-nuclear envelope reappears

-Cytokinesis then produces 4 genetically different haploid gametes (in females only 1 usable egg is produced)

Down Syndrome

results froms trisomy 21

Karotype

a picture of chromosome arranged in homologus pairs

Autosomal chromosomes

chromosome 1-22

Y chromosome purposes

produces a male baby (xy)

Nondisjunction in Meiosis

-occurs when a pair of homologus chromosomes do not seperate properly

Non-disjuncunction in Anaphase I

-homologus chromosomes pair pulls to one side

-results in two n+1 and two n-1 gametes

Non-disjunction in Anaphase II

-sister chromatids fail to seperate

-results in two normal n gametes, one n+1 and one n-1 gamete

Alternation of Generations

-a pattern of reproduction involving a regular alternation between sexual (haploid) or asexual (diploid) forms