Cell Cycle and Nucleic Acids Overview

The Cell Cycle

• A polypeptide's amino acid sequence is programmed by a gene, which is made of DNA.
• DNA is a nucleic acid made of nucleotides.
• Nucleic acids come in two types: DNA and RNA.
• DNA provides instructions for its replication.
• Nucleic acids are polymers called polynucleotides.
• Each polynucleotide is made of monomers called nucleotides.
• A nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups.
• There are two families of nitrogenous bases: pyrimidines (single ring) and purines (double ring).
• Pyrimidines include cytosine, thymine, and uracil.
• Purines include adenine and guanine.
• Thymine is found only in DNA, and uracil is found only in RNA.
• The sugar in DNA is deoxyribose; in RNA, it is ribose.
• DNA has thymine; RNA has uracil.
• Adjacent nucleotides are joined by a phosphodiester linkage.
• DNA is a double helix with two polynucleotides spiraling around an imaginary axis.
• The two backbones in DNA run in opposite directions (antiparallel).
• DNA molecules are typically long, with thousands or millions of base pairs.
• Adenine pairs with thymine; guanine pairs with cytosine.

Somatic vs. Gamete Cells

• Gamete cells are reproductive cells.
• Somatic cells are any cell of a living organism other than reproductive cells.

Cell Division

• Cell division allows organisms to produce more of their kind.
• In unicellular organisms, cell division reproduces the entire organism.
• In multicellular eukaryotes, cell division enables development, renewal, and repair.
• DNA is passed down from one cell generation to the next with remarkable accuracy.

Cell Cycle Summary

• Interphase (chromosome copying): G1 phase, S phase, G2 phase.
• Mitosis (chromosome division).
• Cytokinesis (cell division).
• The cell cycle's phases are Prophase, Prometaphase, Metaphase, Anaphase, and Telophase. The Phases are abbreviated by P-P-M-A-T

Mitotic Spindle

• The mitotic spindle is made of microtubules and associated proteins.
• It controls chromosome movement during mitosis.
• The centrosome is a microtubule-organizing center (in animal cells).
• Spindle microtubules grow out from the centrosomes.

Binary Fission

• Prokaryotes reproduce via binary fission.
• The single chromosome replicates.
• The two daughter chromosomes separate as the cell elongates.
• The plasma membrane pinches inward, dividing the cell into two.

Sexual vs. Asexual Reproduction

• Asexual reproduction produces genetically identical offspring (clones).
• Sexual reproduction involves the fusion of gametes from two parents, creating genetically diverse offspring.

Chromosome Sets in Human Cells

• Human somatic cells have 23 pairs of chromosomes (46 total).
• A karyotype is an ordered display of the homologous pairs of chromosomes.
• Homologous chromosomes are the same length and shape, carrying the same genes.
• The sex chromosomes are called X and Y. Females have XX, males have XY.
• The remaining 22 pairs are called autosomes.
• A diploid cell has two sets of chromosomes (2n); in humans, 2n=46.
• A haploid cell has one set of chromosomes (n); in humans, n=23.

The Human Life Cycle

• Meiosis and fertilization alternate to maintain chromosome number in sexually reproducing organisms.
• The three types of sexual life cycles differ in timing of meiosis and fertilization.

Haploid-Dominant Life Cycle

• In some fungi and algae, the multicellular organism is haploid.
• The zygote is the only diploid stage.
• Haploid cells grow into multicellular forms through mitosis, which produce gametes through mitosis.

Alternation of Generations

• Plants and some algae have both diploid and haploid multicellular stages.
• The diploid stage, called the sporophyte, produces haploid spores by meiosis.
• These spores grow into haploid multicellular forms called gametophytes that produce gametes via mitosis.
• Fertilization of the gametes produces a diploid sporophyte, completing the life cycle.

Origins of Genetic Variation Among Offspring

• Independent assortment of chromosomes.
• Crossing over.
• Random fertilization

The Stages of Meiosis

• Meiosis I separates homologous chromosomes.
• Meiosis II separates sister chromatids as in mitosis but resulting in haploid cells.
• Crossing over and synapsis during prophase I.
• Four haploid cells are produced at the end of meiosis.
• Meiosis reduces the number of chromosome sets from two to one per gamete.

Mendel's Experiments

• Mendel's experiments on pea plants led to principles of inheritance.
• He studied contrasting traits in pea plants.
• He followed the inheritance of these traits across generations.

Mendel’s Laws

• Law of Segregation.
• Law of Independent Assortment.
• Heterozygous vs Homologous

Genetic Vocabulary

• Homozygous - Two identical alleles for a particular gene.
• Heterozygous - Two different alleles for a particular gene
• Phenotype- Observable physical traits.
• Genotype - Genetic Makeup.

Incomplete Dominance

• The heterozygote's phenotype is intermediate between the homozygotes'.
• Example: pink flowers from red and white parent flowers.

Multiple Alleles

• More than 2 alleles exist for a given gene.

Polygenic Inheritance

• More than one gene affects a phenotype trait.

Nature vs Nurture

• Phenotypes determined by both genetic factors and environmental factors.

Recessively Inherited Disorders

• Many genetic diseases are inherited recessively.
• Recessive disorders appear only in individuals homozygous for the recessive allele.
• Carriers are heterozygous for the disorder, but they show no traits.

Pedigree Analysis

• Pedigree analysis tracks traits across family members.
• Pedigree patterns provide clues to inheritance mode.

Sex-Linked Inheritance

• Some genes are located on sex chromosomes.
• Males have one X and one Y; females have two X's.
• X-linked traits show different patterns in males and females.
• Examples of X-linked traits are Red-green colorblindness, and Duchene muscular dystrophy.

Sex Determination and Chromosome Structure

• X-inactivation in female mammals, one of the two X chromosomes in each cell is randomly inactivated.
• Chromosome structure changes can alter phenotype.
• Genetic disorders can arise from changes in chromosome number or structure.

Chromosome Alterations and Disorders

• Large-scale chromosomal alterations often lead to developmental disorders.
• Aneuploidy, a change in the number of chromosomes.
• Polyploidy, more than two sets of chromosomes.

Other Important Considerations

• Environmental factors influence the expression of genetic traits.
• Genetic and environmental factors are involved in many diseases.

This quiz focuses on the cell cycle and the structure of nucleic acids, including DNA and RNA. It covers the composition of nucleotides, the differences between pyrimidines and purines, and the characteristics of DNA and RNA. Test your understanding of these fundamental biological concepts.