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KEY CONCEPT Cells have distinct phases of growth , reproduction , and normal functions. The cell cycle is a regular pattern of growth , DNA replication, and cell division. The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis.
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KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.
The cell cycle is a regular pattern of growth, DNA replication, and cell division.
The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis. • Gap 1 (G1): cell growth and normal functions • DNA synthesis (S): copies DNA • Gap 2 (G2): additional growth • Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis) • Mitosis occurs only if the cell is large enough and the DNA undamaged.
Cells divide at different rates. • The rate of cell division varies with the need for those types of cells. • Some cells are unlikely to divide (G0).
DNA andhistones SupercoiledDNA DNA doublehelix Chromatin Chromosomes condense at the start of mitosis. • DNA wraps around proteins (histones) that condense it.
chromatid telomere centromere telomere Condensed, duplicated chromosome • DNA plus proteins is called chromatin. • One half of a duplicated chromosome is a chromatid. • Sister chromatids are held together at the centromere. • Telomeres protect DNA and do not include genes.
Parent cell centrioles spindle fibers centrosome nucleus with DNA Mitosis and cytokinesis produce two genetically identical daughter cells. • Interphase prepares the cell to divide. • During interphase, the DNA is duplicated.
During prophase, chromosomes condense and spindle fibers form. • Mitosis divides the cell’s nucleus in four phases.
During metaphase, chromosomes line up in the middle of the cell.
During anaphase, sister chromatids separate to opposite sides of the cell.
During telophase, the new nuclei form and chromosomes begin to uncoil.
In animal cells, the membrane pinches closed. • In plant cells, a cell plate forms. • Cytokinesis differs in animal and plant cells.
KEY CONCEPTCell cycle regulation is necessary for healthy growth.
Factors inside & outside cell can regulate cell division. • Death of nearby cells can speed upcell division. • Proteins & hormones can both activate and/or preventcell division. • Over crowding can slow cell division.
webbed fingers • Apoptosis is programmed cell death. • a normal feature of healthy organisms • caused by a cell’s production of self-destructive enzymes • Human embryos have webbing between their fingers and toes. Before the baby is born the cells undergo apoptosis and they are born with unwebbed fingers and toes.
normal cell cancer cell bloodstream Cell division is uncontrolled in cancer. • Cancer cells form disorganized clumps called tumors. • Benign tumors remain clustered and can be removed. • Malignant tumors metastasize, or break away, and can form more tumors.
Carcinogens are substances known to promote cancer. • Standard cancer treatments typically kill both cancerous and healthy cells.
parent cell DNA duplicates cell begins to divide daughter cells Binary fission is similar in function to mitosis. • Asexual reproduction is the creation of offspring from a single parent. • Binary fission produces two daughter cells genetically identical to the parent cell. • Binary fission occurs inprokaryotes (cells without a nucleus).
KEY CONCEPT Cells work together to carry out complex functions.
SYSTEMS leaf shoot system stem vascular tissue CELL TISSUE ORGAN root system lateral roots primary root Multicellular organisms depend on interactions among different cell types. • Tissues are groups of cells that perform a similar function. • Organs are groups of tissues that perform a specific or related function. • Organ systems are groups of organs that carry out similar functions.
Inner: intestines Outer: skin cells Middle: bone cells Specialized cells perform specific functions. • Cells develop into their mature forms through the process of cell differentiation. Cells differ because of genes and location in an embryo. • Stem cells have the ability to • divide and renew themselves • remain undifferentiated in form • develop into a variety of specialized cell types
The use of stem cells offers many current and potential benefits. • Stem cells are used to treat leukemia and lymphoma. • Stem cells may cure disease or replace damaged organs. • Stem cells may revolutionize the drug development process.
KEY CONCEPT Gametes (sex cells) have half the number of chromosomes that body (somatic) cells have.
Your cells have autosomes and sex chromosomes. • Your body cells have 23 pairs of chromosomes; homologous pairs of chromosomes have the same structure; for each homologous pair, one chromosome comes from each parent. • Chromosome pairs 1-22 are autosomes. • Sex chromosomes, X and Y, determine gender in mammals.
Body cells are diploid; gametes are haploid. • Fertilization between egg and sperm occurs in sexual reproduction. • Diploid (2n) cells have two copies of every chromosome. • Body cells are diploid. • Half the chromosomes come from each parent.
Haploid (n) cells have one copy of every chromosome. • Gametes are haploid. • Gametes have 22 autosomes and 1 sex chromosome.
Meiosis differs from mitosis in significant ways. • Meiosis has two cell divisions while mitosis has one. • In mitosis, homologous chromosomes never pair up. • Meiosis results in haploid cells; mitosis results in diploid cells.
KEY CONCEPT Mendel’s research showed that traits are inherited as distinct units.
Mendel laid the groundwork for genetics. • Traits are distinguishing characteristics that are inherited. • Genetics is the study of biological inheritance patterns and variation. • Gregor Mendel showed that traits are inherited as discrete units. • Many in Mendel’s day thought traits were blended.
Mendel’s data revealed patterns of inheritance. • Mendel made three key decisions in his experiments. • use of purebred plants • control over breeding • observation of seven“either-or” traits
Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. • Mendel used pollen to fertilize selected pea plants. • P generation crossed to produce F1 generation • interrupted the self-pollination process by removing male flower parts
Mendel allowed the resulting plants to self-pollinate. • Among the F1 generation, all plants had purple flowers • F1 plants are all heterozygous (same gene type expressed) • Among the F2 generation, some plants had purple flowers and some had white
The same gene can have many versions. • A gene is a piece of DNA that directs a cell to make a certain protein. • Each gene has a locus, aspecific position on a pair ofhomologous chromosomes.
An allele is any alternative form of a gene occurring at a specific locus on a chromosome. • Each parent donates one allele for every gene. • Homozygous describes two alleles that are the same at a specific locus (location on DNA). • Heterozygous describes two alleles that are different at a specific locus.
Genes influence the development of traits. • All of an organism’s genetic material is called the genome. • A genotype refers to the makeup of a specific set of genes. • A phenotype is the physical expression of a trait.
Alleles can be represented using letters. • A dominant allele is expressed as a phenotype when at least one allele is dominant. • A recessive allele is expressed as a phenotype only when two copies are present. • Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.
Punnett squares illustrate genetic crosses. • The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. • The axes representthe possible gametesof each parent. • The boxes show thepossible genotypesof the offspring. • The Punnett square shows the possible genotypes and phenotypes. Usually shown as a percentage or fraction.
Probability = number of ways a specific event can occur number of total possible outcomes Heredity patterns can be calculated with probability. • Probability is the likelihood that something will happen. • Probability predicts an average number of occurrences, not an exact number of occurrences.
