dna, mitosis and meiosis lindsey bily anatomy & physiology austin high school
TRANSCRIPT
History of DNA
Frederick Griffith
-1928 experimented with Strep bacteria and was able to transform them from one form to another. Found a “ transforming factor”.
History of DNA
• Rosalind Franklin– 1952: took a picture of DNA by X-ray diffraction
which was used to determine the double helical structure of DNA
History of DNA
• Watson & Crick
– 1953: Used the image of DNA by Rosalind Franklin to determine that the structure of DNA is in a double helix.
DNA Structure
• Nucleotides differ in their nitrogenous base component.
Purines: Adenine and guanine
Pyrimidines: Cytosine and thymine
Transcription
• DNA cannot exist outside of the nucleus. It will be degraded by enzymes in the cytosol.
• DNA’s “message” has to get out to the cytoplasm where proteins are made.
• mRNA is used to transcribe DNA’s message.
Transcription
• DNA unzips at the gene where the DNA is to be transcribed.
• RNA nucleotides attach to the DNA strand.
• Complimentary Base Pairing
A binds with U (uracil, no thymine)
G binds with C
Transcription
• The mRNA has to be edited before it can leave the nucleus.
• Introns are areas of noncoding DNA. These are removed from the mRNA.
• The coding parts (exons) are kept on the mRNA and spliced or joined together.
We can now leave the nucleus!
Transcription
• Animation (click on website)
http://content.dnalc.org/content/c15/15510/transcription_basic.mp4
Translation
• The mRNA moves into the cytoplasm and it attracts lots of ribosomes.
• Let’s translate the DNA code!
Translation
• tRNA (transfer RNA) molecules carry amino acids. – Each tRNA carries 1
amino acid– The tRNA’s anticodon
binds to the codon on the mRNA strand
Translation to Protein
• Once the polypeptide chain has been formed, the enzymes in the Rough ER, Golgi, and cytoplasm help them to fold in their 1, 2, 3, or 4 structure.
Cell Growth and Reproduction
• Cell Growth: using the DNA to make the proteins needed for survival.
• Cell Reproduction: DNA is passed from one generation of cells to the next and from one generation of organisms to the next.
Cell Growth
• The cell produces new structural proteins and all the enzymes needed to make lipids, carbohydrates, and other substances.
Cell Growth
• The cell must make additional cytoplasm and plasma membrane as the cell grows.
• Membranous organelles (ER, Golgi, lysosomes, peroxisomes) are made up of the same material as the plasma membrane and must also be made as the cell grows.
• Mitochondria have their own DNA
and replicate themselves.
DNA Replication
• As a cell becomes larger, this triggers the replication of DNA.
• Replication of DNA is very similar to the formation of mRNA (transcription)
DNA Replication
2. Nucleotides floating in the nucleus pair with the unzipped bases in the DNA strands.
DNA Replication
4. As nucleotides bind to the DNA strands, two new, identical DNA molecules are formed. These are called chromatids.
Practice
The original DNA strand is shown below. Please write down the sequence of the complimentary strand that forms during DNA Replication.
ATTCGTAGGCC
TAAGCATCCGG
DNA Replication
• Click on the website for animation.
http://www.dnalc.org/resources/3d/03-mechanism-of-replication-basic.html
Cell Reproduction: Mitosis
• One parent cell becomes 2 daughter cells.
• The plasma membrane splits into two via cytokinesis (“cell movement”).
Cell Reproduction: Mitosis
• Phase 1: InterphaseThe cell is not growing, but is not reproducing
either. It is PREPARING for reproduction. DNA is being replicated.
Cell Reproduction: Mitosis
Phase 2: ProphaseThe nuclear envelope falls apart. The paired chromatids form chromosomes. The centrioles move towards the “poles” of the cell. Spindle fibers are formed between them.
Cell Reproduction: Mitosis
• Phase 3: Metaphase“Position changing phase”.
Chromosomes are no longer in the nucleus and line up at the “equator” of the cell. One chromatid faces one pole, the sister chromatid faces the other pole and become attached to spindle fibers.
Cell Reproduction: Mitosis
• Phase 4: Anaphase“Apart Phase”. The
spindle fibers pull the sister chromatids apart from each other towards the opposite poles of the cell.
Cell Reproduction: Mitosis
• Phase 5: Telophase“End Phase”. DNA is
returned to its original form. The nuclear envelope rebuilds. Chromosomes elongate into chromatin again. Spindle fibers disappear. Cytokinesis happens.
Cell Reproduction: Meiosis
• Cell division that occurs in the sex cells ONLY.
• Primitive sex cells (spermatogonia and oogonia) become mature gametes (sperm and an ovum).
Cell Reproduction: Meiosis
• DIPLOID: All somatic (body) cells have 46 chromosomes that are in 23 pairs.
• HAPLOID: Meiosis reduces the number of chromosomes in the primitive sex cells by half. 23 total chromosomes.
Two Phases: Meiosis I And Meiosis II