Cell Division and DNA Replication

• Test 4 covers asexual and sexual reproduction, cell cycle and mitosis, DNA, DNA replication, and protein synthesis.

Sexual and Asexual Reproduction

• Asexual reproduction involves offspring having DNA from one parent, creating clones, common in bacteria, plants, and many invertebrate animals.
• Sexual reproduction involves mating; offspring are different from their parents, common in most animals and plants.
• Sexual reproduction occurs when cells from both parents combine, two gametes unite to form a zygote; gametes include sperm and egg.

Advantages and Disadvantages of Asexual and Sexual Reproduction

• Asexual reproduction enables faster offspring production without needing a partner
• Asexual reproduction results in genetically identical offspring, limiting adaptation to environmental changes
• Asexual reproduction increases the risk of entire populations being wiped out due to a single disease.
• Sexual reproduction introduces variation, enabling species to adapt better
• Sexual reproduction takes longer and requires finding a partner
• Sexual reproduction means offspring only receive half of each parent’s DNA

Cell Cycle and Mitosis

• Multicellular organisms undergo cell division for growth, wound repair, replacing old cells, reproduction, and fighting infection

Stages of the Cell Cycle

• G1 phase is for growth until the cell doubles in size; new proteins and organelles are made
• S phase is for DNA synthesis where chromosomes are replicated into two identical sister chromatids attached by a centromere
• In cell division, chromatids separate, giving each new cell one chromatid
• G2 phase produces organelles and molecules for cell division, preparing for mitosis

Mitosis: Division of the Cell Nucleus

• Prophase condenses chromosomes from chromatin. Condensation of the centrioles occur, which move to opposite poles and spindle fibers begin to form. The nuclear envelope starts to break down here.
• Metaphase sees spindle fibers attach to sister chromatids at the kinetochore region and chromosomes line up single-file at the cell's center.
• Anaphase involves the cell elongating. Shortening of the Microtubules pull apart sister chromatids, which move towards opposite sides
• Telophase involves two new nuclear envelopes forming around the chromosomes; spindle fibers disintegrate and chromosomes decondense into chromatin.

Cytokinesis: Division of the Cytoplasm

• In animal cells, the cell membrane pinches to form two daughter cells, each with identical DNA
• In plant cells, a cell plate forms midway between the divided nuclei
• Interphase occupies most of the cell's life cycle; mitosis is swift
• It's important to know the appearance of cells and chromosomes during mitosis stages.

Cell Division

• During cytokinesis, animal cells divide via the cell membrane pinching inward to form two daughter cells; each with an identical DNA set
• Plant cells divide a cell plate forms midway between the divided nuclei.
• Daughter cells from mitosis are identical to the parent cell

Cell Cycle Regulation

• The cell cycle is regulated at three checkpoints (G1, G2, and mitosis checkpoint) and G0 phase
• Cells decide whether to proceed with cell division based on internal and external conditions

Cell Cycle Checkpoints

• The G1 checkpoint assesses cell size, nutrients, growth factors, and DNA damage before S phase
• The G0 phase is entered if a cell decides not to divide again
• Cells in G0 perform normal functions without dividing, such as muscle and brain cells
• The G2 checkpoint occurs before mitosis, checking for DNA damage and complete replication during S phase; it allows time for repairs or apoptosis
• The mitosis checkpoint, between metaphase and anaphase, ensures all sister chromatids are attached to the spindle at the metaphase plate. APC promotes anaphase

Failed Cell Cycle Regulation

• Failed regulation can lead to cancer, which is uncontrolled cell division

DNA

• DNA is a nucleic acid; its monomer is a nucleotide
• DNA elements include carbon, hydrogen, oxygen, nitrogen, and phosphorus

Nucleotide Components

• Nucleotides include a 5-carbon sugar (deoxyribose or ribose), a nitrogenous base, and a phosphate group'
• Chargaff's rule states that [A]=[T] and [C]=[G]
• Given the amount of one base, determine the percentage of A, T, C, or G, the fact to note here is A=T, C=G

DNA Functions and Location

• DNA stores genetic information and codes for traits (proteins) and is located in the cell nucleus
• The DNA structure has a sugar-phosphate backbone and bases as rungs, held by hydrogen bonds

DNA Organization

• The arrangement from smallest to largest is nucleotide, gene, chromatid, chromosome, and nucleus
• Hydrogen bonds are weak bonds connecting DNA strands

DNA Replication

• DNA replication is needed to give daughter cells an identical DNA set as the parent cell

DNA Replication Steps

• Helicase unwinds the double helix by breaking hydrogen bonds between base pairs (unzips)
• DNA polymerase adds new nucleotides to the original strand by base pairing to synthesize a new DNA strand (complementary)

DNA Enzymes

• Ligase connects Okazaki fragments on the lagging strand
• Helicase unwinds the double helix
• DNA polymerase adds new nucleotides to synthesize strands

Additional Replication Facts

• Each strand in the original DNA molecule is a template for new, complementary strands
• The replication fork is the area where two DNA strands separate

DNA Polymerase

• DNA polymerase synthesizes DNA in the 5' to 3' direction, presenting challenges during replication
• The leading strand is synthesized continuously
• Lagging strands are made in short Okazaki fragments
• The leading strand synthesizes in the same direction as the replication fork and is continuous
• The lagging strand starts at the replication fork, moves in the opposite direction, and is discontinuous
• Semiconservative replication is when each DNA strand is half new, half old

RNA

• RNA is a nucleic acid; its monomers are nucleotides

Comparing DNA and RNA

• RNA's sugar is ribose, not deoxyribose.
• RNA is single-stranded, not double-stranded
• RNA contains uracil instead of thymine

RNA Functions

• mRNA (messenger RNA) carries code from gene to ribosome
• tRNA (transfer RNA) carries amino acids to ribosomes for protein synthesis. rRNA (ribosomal RNA) comprises ribosomes.

Protein Synthesis

• Two key steps include transcribing DNA into RNA then translating it into a peptide.
• Transcription synthesizes mRNA from DNA in the nucleus
• Translation synthesizes proteins from mRNA in the ribosomes in/of the cytoplasm

Test your knowledge of cell division, including mitosis, and DNA replication processes. Questions cover the phases of the cell cycle, enzyme functions, and the differences between sexual and asexual reproduction. Also covers Okazaki fragments and the role of the centromere.