DNA, Mitosis and Meiosis Lindsey Bily Anatomy & Physiology Austin High School.

DNA, Mitosis and Meiosis

Lindsey Bily

Anatomy & Physiology

Austin High School

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

• Deoxyribonucleic Acid: a HUGE molecule and the most important molecule in the world!

DNA Structure

• DNA is a polymer made up of millions of nucleotides. (phosphate, sugar, and base)

DNA Structure

• Nucleotides differ in their nitrogenous base component.

Purines: Adenine and guanine

Pyrimidines: Cytosine and thymine

DNA Structure

• Obligatory Base Pairing– A binds T

– C binds G

ALWAYS!!

DNA Structure

• Guanine pairs with Cytosine via 3 Hydrogen bonds (lit area)

DNA Structure

• Adenine pairs with Thymine via 2 Hydrogen bonds (lit area).

DNA Structure

• Sugar Phosphate backbone.

• Base pairings are the rungs of the “ladder”.

Genes

• Genes are a segment of DNA that code for proteins.

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

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!

Ribosomes on mRNA

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 Animation

•http://content.dnalc.org/content/c15/15501/translation_basic.mp4

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

1. DNA uncoils or “unzips” except for small segments.

DNA Replication

2. Nucleotides floating in the nucleus pair with the unzipped bases in the DNA strands.

DNA Replication

3. DNA Polymerase causes the new nucleotides to bind with the unzipped 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”).


• Phase 1: InterphaseThe cell is not growing, but is not reproducing

either. It is PREPARING for reproduction. DNA is being replicated.


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.


• 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.


• Phase 4: Anaphase“Apart Phase”. The

spindle fibers pull the sister chromatids apart from each other towards the opposite poles of the cell.


• 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.

Mitosis Animation

• Click on the website for Mitosis animation.

• http://vimeo.com/8333643

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).


• 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

DNA, Mitosis and Meiosis Lindsey Bily Anatomy & Physiology Austin High School.

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