deoxyribonucleic acid - dna found primarily in the nucleus in chromosomes - stores and transmit...
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Nucleic Acids
Deoxyribonucleic Acid - DNA Found primarily in the nucleus in chromosomes - stores
and transmit information to make proteins. Structure
Consists of two strands of nucleotide monomers Parts of a nucleotide
Deoxyribose - 5-carbon sugar Phosphate group Nitrogen base
Nucleic Acids
Nitrogen base Purine - nitrogen base with a double ring of
carbon and nitrogen atoms. AdenineGuanine
Pyrimidine - nitrogen base having a single ring of carbon and nitrogen atoms.
ThymineCytosine
Nucleic AcidsTwo strands of nucleotides twist around a central axis to form
a double helixFirst described by Watson and Crick in 1953. Similar to a twisted ladder
Sides of alternating sugar and phosphateRungs consist of pairs of nitrogen bases -
equal in length. Purine always pairs with a pyrimidine -have hydrogen bonds.
Adenine bonds with thymine Guanine bonds with cytosine
Nucleic Acids
Base sequence one strand is exact complement of base sequence in second strand.
1st Strand Sequence A - G - C - T - T - A - G - C
2nd Strand Sequence T - C - G - A - A - T - C - G
Nucleic Acids
Replication
Process of duplicating the DNA molecule
Each strand serves as a template or mold for new complementary strand to be built.
Nucleic Acids
Process of Replication
DNA helicase attaches to DNA molecule - "unzips" the 2 strands - breaks hydrogen bonds between bases.
Unpaired bases of strands react with complementary bases of nucleotides in nucleus - hydrogen bonds form.
DNA polymerase catalyzes formation of sugar to phosphate bonds - connect one nucleotide to the next.
Result - two new DNA molecules - each consists of 1 "old" strand and 1 "new" strand.
Process doesn't begin at one end and proceed to the other - may occur simultaneously at many points.
Nucleic Acids
DNA may be damaged by body heat, radiation, chemicals, etc.
Cell can "proofread" for mistakes
Can be repaired and corrected
Nucleic AcidsRibonucleic Acid – RNA
Nucleic acid that uses information stored in DNA to synthesize proteins.
StructureConsists of a single strand of nucleotide monomers.Parts of nucleotide
Ribose - 5-carbon sugarPhosphate groupNitrogen base
Nucleic Acids
RNA differs from DNA in 3 ways RNA consists of only one strand of
nucleotides instead of the 2 strands of DNA. RNA contains the 5-carbon sugar, ribose,
instead of deoxyribose RNA contains the nitrogen base, uracil,
instead of thymine.
Nucleic AcidsTypes of RNA Messenger RNA (mRNA) - single, uncoiled strand,
transmits information from DNA for protein synthesis; acts as template for amino acid assembly during protein synthesis at ribosomes.
Transfer (tRNA) - single strand of RNA folded back on itself in hairpin fashion; allows some bases pairing; exists in 20 or more varieties each for only 1 specific type of amino acid.
Ribosomal RNA (rRNA) - globular form of RNA; major constituent of ribosomes.
Nucleic Acids Transcription
Process where mRNA is produced from the DNA - transcribed according to the information coded in the base sequence of DNA. Base sequence of mRNA complementary to sequence of DNA from which it was transcribed. Directed by enzyme, RNA polymerase
Process Enzyme binds to DNA causing strands to separate. Hydrogen bonds to form between DNA template and complementary RNA nucleotide bases. Enzyme moves to next section of DNA, bonds form between phosphate groups and ribose. RNA molecule released when enzyme reaches DNA sequence that acts as a termination signal.
Nucleic AcidsProtein Synthesis Structural and functional characteristics of proteins are determined by the
sequence of amino acids in the protein
Sequence of amino acids in a protein encoded in DNA
Genetic Code - System that contains information needed by cells for proper functioning; built into the arrangement of nitrogen bases in a particular sequence of DNA.
Codon - series of three bases in mRNA that codes for a specific amino acid.
Anticodon - series of three bases in tRNA, complementary to a codon; pairs with the codon during translation
Nucleic AcidsTranslation - process where protein molecules are made from
information encoded in mRNA. mRNA moves out of nucleus through a nuclear pore mRNA migrates to a group of ribosomes Amino acids in the cytoplasm are transported to the ribosomes by tRNA
- each specific for an amino acid. Assembly of polypeptide begins when A - U - G codon attaches to the
ribosome. Codon pairs with its anticodon adding specific amino acid to the
growing polypeptide chain. Process continues until a "stop" codon reaches the ribosome. mRNA is released and polypeptide is complete and released
Nucleic Acids
Gene - region of DNA that directs the formation of a polypeptide.
Proteins usually consist of more than
one polypeptide.
Several genes may direct protein synthesis
Cell DivisionProcess by which cells reproduce. Cell Theory
Cell is basic unit of life Living things are made of cells or cell
fragments. All cells come form existing cells.
Reasons Cells Divide Maintenance Repair Growth Reproduction
Cell DivisionNucleus Organelle that directs the everyday metabolic activities of the cell. Composed of Chromatin
Normally - grainy mass of material During cell division appear as bodies called chromosomes. Composed of DNA and protein Carries the "genetic code" Individual heredity units are genes - determine cell characteristics
and how cell functions - by proteins that are synthesized. Each time the cell divides the genetic material must be replicated – makes
exact copy Must then be distributed to the new cell. Replication occurs during interphase.
Cell DivisionChromosome Number The number of chromosomes found in the nucleus.
Varies from one organism to another. Man - 46 Fruit Fly - 8 Bullfrog - 26
All cells of an organism will have the same number of chromosomes.
Exception is the sex cells or Gametes Egg - female Sperm - male
Body cells called Somatic Cells or Somates.
Cell DivisionHumans 23 pairs of chromosomes - total of 46 chromosomes. Pairs of chromosomes are known as being Homologous.
Individual members of the pair are called Homologs. Get one homolog of each pair from each parent Each homolog of pair has same size and shape.
Number of pairs of chromosomes in a somate is expressed as "n" - total number of chromosomes expressed as "2n"
Humans: n = 23; 2n = 46 Total number of chromosomes is Diploid Number = 2n Total number of different pairs in cell is its Haploid Number
(Monoploid) = n Features of the cell's chromosomes including size and number
make up cell's Karyotype - arranged by size and shape.
Cell DivisionActually talking about division of nuclear
material
Two types of nuclear division MitosisMeiosis
Cytokinesis - division of the cytoplasm
MitosisProcess by which the nucleus divides to produce 2 new nuclei, each with the
same number of chromosomes as the parent nucleus. From the Greek - Mitos - Thread Occurs in somatic cells.
Requirements Precise replication of the genetic material Distribution of a complete set of chromosomes to each new cell -
called Daughter Cells Five Phases of Cell Cycle - continuous
Interphase Prophase Metaphase Anaphase Telophase
MitosisInterphase – not really a part of mitosis
Once called the "resting" stage Cell performing various metabolic activities Occupies about 2/3 of cell's life cycle Genetic material replicates during phase. Nucleus clearly defined by membrane Chromosomes not visible - chromatin appears grainy. Consists of 3 subphases
G1 Phase - first phase of interphase; cell doubles in size; enzymes and organelles,roughly double in size.
S Phase - DNA in the chromatin replicates G2 Phase - Cell undergoes rapid growth that prepares it for
mitosis, synthesizing necessary enzymes and structures.
MitosisProphase
Early prophase - chromatin coils; forms chromosomes. Chromosomes appear as rod-like structures. Nucleolus and nuclear membrane breakdown and disappear. Centrioles appear next to the disappearing nucleus - move to
opposite ends or poles of cell (not plants). Spindle fibers form - asters radiate from centrioles in animal
cells. Chromosomes appear as double stranded structure
Each strand is a Chromatid Two chromatids are joined at a Centromere.
MitosisMetaphase
Chromosomes arrange themselves on equator of spindle
Chromosomes attach to spindle fibers at the centromere.
Centromeres aligned on the equator.
MitosisAnaphase Centromere divides - one chromatid
moves toward 1 pole of spindle while other chromatid moves to the opposite pole.
MitosisTelophase
Two identical sets of chromatids are clustered at opposite ends of the cell.
Centrioles and spindle fibers disappear.
Chromatids unwind and elongate into chromatin - chromosomes disappear
Nuclear membrane and nucleolus reappear.
Mitosis Process completed with cytokinesis - get two
distinct cells Animals – Cleavage Furrow forms from
outside toward the center – pinches cell in two.
Plants – Cell Plate forms from center and grows to the outside.
No reduction in chromosome number Parent Cell = 2n ----> Each Daughter Cell =
2n
MeiosisProcess by which the cell nucleus divides resulting in a reduction of
chromosome number from the diploid number (2n) to the haploid number (n)
Involves 2 divisions Chromosome number reduced in first division - Meiosis I Second division - mitotic - Meiosis II
Cell division that results in formation of gametes or sex cells. Occurs in the Gonads (sex organs)
Ovary - female Testes - male
Process in males - called Spermatogenesis Process in females - called Oogenesis
MeiosisPhases
Interphase Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II
MeiosisProphase I DNA strands coil, shorten, and thicken- Chromosomes become
visible. Nuclear membrane disappears, spindle fibers appear. Homologous pairs of chromosomes move together - Homologs
pair Pairing movement is called Synapsis Two double stranded chromosomes are so close
they appear to be joined at their centromeres. Looks like 4 chromatids connected – group called a
Tetrad. Crossing Over of chromatids may occur during synapsis
Meiosis
Metaphase I Tetrads align on the equator of the cell
Have 2 chromosomes with 4 chromatids attached to single spindle fiber.
Meiosis
Anaphase I Homologous pairs of chromosomes separate -
one chromosome of the pair goes to each pole - centromeres do not divide.
Each chromosome still consists of 2 chromatids joined by a centromere.
Meiosis
Telophase I Cytoplasm divides to form 2 daughter cells. Nuclear membrane begins to reappear, double
stranded chromosomes disappear; spindle may disappear.
Each daughter cell contains one half the original number of chromosomes that parent cell had.
Cells may enter resting state – Interkinesis
Meiosis
Metaphase II Chromosomes move to cell's equator. Centromere attaches to spindle fiber. Each chromosome composed of sister
chromatids joined at centromere.
Meiosis
Anaphase II Centromere joining chromatids divides. Each chromatid moves toward the
opposite pole.
Meiosis
Telophase II Spindle disappears Nuclear membrane forms around
chromosomes of each daughter cell. Each of the 4 cells formed from the original
parent cell has 1/2 the number of chromosomes of the parent.
Meiosis
Summary First Meiotic Division - produces 2 haploid
cells; double stranded chromosomes. Second Meiotic Division - 2 haploid cells
divide to produce 4 haploid cells. 4 haploid cells can develop into gametes.
Spermatogenesis and Oogenesis
Cells at the end of Prophase I
Male - Primary Spermatocyte – at puberty Female - Primary Oocyte - formed as early as
3rd month of development - meiosis stops until sexual maturity
Spermatogenesis and Oogenesis
Two cells at the end of Telophase I Male - secondary spermatocyte
Female - cells unequal - 1 secondary oocyte, 1 polar body
Spermatogenesis and Oogenesis
Cells at end of Telophase II Male - 4 haploid cells – Spermatids
Female - 1 Ootid and 3 Polar Bodies (die) - ootid has most of the cytoplasm.
Spermatogenesis and Oogenesis
Importance
Ensures that chromosome number remains constant in sexual reproduction
Egg (n) + Sperm (n) -- Fertilization --> Zygote (2n)
Chromosome number of zygote is thus the same as the two parents.
Types of Reproduction
Asexual - production of offspring from one parent
No fusion of gametes Offspring is identical to parent. Occurs due to mitosis. No genetic variation between parent
and offspring
Types of Reproduction
Sexual - production of offspring through meiosis and subsequent fusion of gametes from two parents
Offspring is different from either parent Half of genetic material has come from one
parent; other half has come from the other parent.
Introduces variation between the parents and offspring.