Sexual vs Asexual Reproduction

• Study notes for sexual and asexual reproduction, cell cycle and mitosis, DNA and RNA structure and replication, and protein synthesis

Sexual and Asexual Reproduction

• Asexual reproduction involves one parent.
• Offspring in asexual reproduction have the same DNA as their parent.
• Asexual reproduction is present in bacteria, some plants, and many invertebrates.
• Sexual reproduction involves two parents.
• Mating is required for sexual reproduction.
• Sexual reproduction is common in most animals and plants.
• Offspring in sexual reproduction differ from their parents.
• Sexual reproduction combines cells from both parents.
• Two gametes (sperm and egg) unite to form a zygote (fertilized egg).

Advantages and Disadvantages of Sexual and Asexual Reproduction

• Sexual reproduction leads to variation, enabling species to adapt.
• Asexual reproduction allows for faster offspring production without needing a partner.
• Sexual reproduction requires more time to find a partner.
• Offspring in sexual reproduction only receive half of each parent's DNA.
• Asexual reproduction results in genetically identical offspring that cannot adapt.
• One disease can wipe out an entire population in asexual reproduction.

Cell Cycle and Mitosis

• Body/somatic cells are all cells in the body except sperm and egg cells.
• Multicellular organisms undergo cell division for growth.
• Cell division is used for wound repair/healing.
• Cell division helps fight infection.
• Cell division aids reproduction.
• Cell division replaces old or dead cells.
• The cell cycle includes interphase and cell division.
• Interphase is a period of growth and preparation between cell divisions.

Interphase

• G1 phase: Cell grows until it doubles in size, makes new proteins and organelles, and carries out its functions.
• S phase: DNA is replicated during DNA synthesis so the new cell has directions for its function.
• G2 phase: Organelles and molecules required for cell division are produced, and the cell checks for mistakes.

Cell Division - Mitosis

• Prophase: Chromosomes condense, the nuclear envelope breaks down, centrioles move to opposite poles, and spindle fibers form.
• Metaphase: Spindle fibers attach to sister chromatids, and chromosomes line up at the center of the cell.
• Anaphase: The cell elongates, microtubules shorten, and sister chromatids are pulled apart toward opposite sides.
• Telophase: Two new nuclear envelopes form around the chromosomes, spindle fibers disintegrate, and chromosomes decondense.
• Cytokinesis: The cell's cytoplasm divides into two separate cells, resulting in two new daughter cells from one parent cell.
• Cells will not divide if conditions are not right, such as when there is not enough space or if DNA is damaged.

Timing and Differences in Cell Division

• Cells spend most of their life in interphase.
• Mitosis/cytokinesis takes around 1 to 2 hours.
• In plants, a cell plate forms during cytokinesis.
• In animals, the cell membrane pinches to form two daughter cells.
• Daughter cells are genetically identical to the parent cell in mitosis.

Cell Cycle Regulation

• The cell cycle includes interphase, mitosis, and cytokinesis

Cell Cycle Checkpoints and Regulation Failure

• G1 checkpoint: Determines whether a cell will divide and commits the cell to divide.
• G2 checkpoint: Checks for DNA damage and complete copying during S phase, pausing for repairs or apoptosis if needed.
• Mitosis checkpoint: Ensures that all sister chromatids are attached to spindle fibers at the metaphase plate.
• G0 phase: Cells enter this phase if they decide not to divide, carrying on normal functions.
• Some cells stay in G0 forever, like muscle and brain cells.
• Abnormal cell division can occur when regulation fails.
• Cancer cells grow without signals, differing from normal cells in cell division behavior.

DNA

• DNA stands for deoxyribonucleic acid.
• RNA stands for ribonucleic acid.
• DNA is a nucleic acid macromolecule, and its monomer is a nucleotide.
• Nucleotides are joined into long strands or chains by covalent bonds.
• DNA is composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus.

Nucleotide Components and Chargaff's Rule

• Nucleotides contain a 5-carbon sugar (deoxyribose or ribose), a nitrogen base, and a phosphate group.
• Chargaff’s rule states that [A] = [T] and [C] = [G] (A=adenine, T=thymine, C=cytosine, G=guanine).
• Chargaff’s rule helped discover the structure of DNA.

DNA Structure

• The function of DNA is to store genetic information and code for traits (proteins).
• DNA is located in the nucleus.
• DNA consists of two strands bound together by hydrogen bonds in a double helix shape.
• DNA has a sugar-phosphate backbone made of alternating deoxyribose and phosphate.
• Bases in the middle of the DNA molecule are attached to their pairs by hydrogen bonding.
• Complementary base pairing means that specific bases always pair: A = T and G = C.
• Antiparallel DNA strands run in opposite directions, allowing base pairs to align properly and form the double helix.

DNA, Genes, Chromosomes, Nucleotides, and Chromatids

• Genes are coded DNA instructions that direct the productions of proteins within the cell.
• Chromosomes are tightly coiled pieces of DNA found in the nucleus.
• A nucleotide is the basic building block of DNA
• A chromatid is one of the two identical halves of a chromosome that has been replicated in preparation for cell division.
• Nucleotides are inside genes, genes are on chromosomes, and chromosomes create sister chromatids during replication; all are in the nucleus.
• Hydrogen bonds are the weak bonds that connect the two strands of DNA.

DNA Replication

• DNA needs to be replicated so that each daughter cell has a full set.

Steps of DNA Replication

• Helicase unwinds the double helix by breaking hydrogen bonds.
• DNA polymerase adds new nucleotides to the open DNA strand, using each strand as a template.
• Ligase connects Okazaki fragments in the lagging strand.
• Helicase unwinds the double helix.
• DNA polymerase adds new nucleotides.
• Ligase connects fragments.
• The replication fork is the area where two DNA strands are being separated.
• DNA polymerase synthesizes DNA only in the 5’ to 3’ direction.

Leading vs Lagging Strand

• The leading strand is synthesized continuously in the same direction as the growing replication fork.
• The lagging strand starts at the replication fork and moves in the opposite direction discontinuously.
• Okazaki fragments are small sections of DNA formed during discontinuous synthesis of the lagging strand.
• DNA replication is semi-conservative because half of each DNA strand is new, and half is old.
• The old strand acts as a template for the new strand, allowing for fast, accurate replication and easy repair.

RNA Structure Differences and Functions

• RNA is composed of nucleotides which each have a ribose sugar, a phosphate group, and a nitrogenous base (adenine, cytosine, guanine, or uracil)
• The sugar in RNA is ribose instead of deoxyribose.
• RNA is single-stranded, not double-stranded.
• RNA contains uracil while DNA contains thymine.
• DNA = deoxyribonucleic acid.
• RNA = ribonucleic acid.
• mRNA (messenger RNA) carries instructions from DNA in the nucleus to ribosomes in the cytoplasm.
• rRNA (ribosomal RNA) makes up ribosomes.
• tRNA (transfer RNA) brings amino acids to the ribosomes.

Protein Synthesis

• Protein synthesis involves transcribing DNA into RNA and translating the RNA into a polypeptide.
• Transcription copies a gene from DNA into mRNA in the nucleus.
• Translation uses the mRNA code to make a protein (polypeptide) at the ribosomes in the cytoplasm.

Notes about sexual and asexual reproduction. Includes the advantages and disadvantages of each method. Sexual reproduction leads to variation, enabling species to adapt. Asexual reproduction allows for faster offspring production without needing a partner.