Nucleus
• Information Central |
• It houses most of the cell’s DNA |
• It contains most of the genes in the eukaryotic cell |
• Most conspicuous (noticeable) structure in eukaryotic cells (5 μm) |
Nucleolus (Nucleoli)
Non-membranous structure involved in production of ribosomes |
Nucleus has one or more nucleoli |
Nuclear envelope
Encloses the nucleus |
Separates its contents from the cytoplasm |
Double membrane |
Perforated by pores |
Pore complex lines regulates entry and exit of proteins, RNAs, and large complexes of macromolecules |
Continuous with ER |
Chromatin
Consist of DNA and proteins |
Makes up chromosomes |
Visible in a dividing cell as individual condensed chromosomes |
Endomembrane system
Includes: nuclear envelope, ER, Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, plasma membrane |
ENDOPLASMIC RETICULUM (ER)
Biosynthetic Factory |
endoplasmic - within the cytoplasm |
It is continuous with the nuclear envelope |
reticulum - little net |
Rough ER |
Smooth ER |
Ribosomes on the outer surface |
Lacks ribosomes on outer surface |
Synthesis of lipids, metabolism of carbohydrates |
Synthesis of secretory and other proteins on bound ribosomes |
Ca²+ storage |
adds carbohydrates to proteins to make glycoproteins |
Detoxification of drugs and poisons |
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Golgi apparatus
Shipping and Receiving Center |
Active in synthesis, modification, sorting, and secretion of cell products |
Warehouse for receiving, sorting, shipping, and even some manufacturing |
Cis face |
Trans face |
receiving face, in which the vesicles empty their content |
through which the vesicles leave the Golgi apparatus |
Lysosome
Digestive organelle where macromolecules are hydrolyzed |
hydrolytic enzymes that an animal cell uses to digest (hydrolyze) macromolecules. |
Peroxisome
Oxidation |
Contain enzymes that remove hydrogen atoms from various substrates and transfer them to oxygen |
Produces hydrogen peroxide as a by-product, then converts it to water |
Ribosomes
Protein Factories |
Made of ribosomal RNA and protein |
Free ribosomes (Cytosol) |
Carry out protein synthesis |
Bound ribosomes (ER and Nuclear Envelope) |
Not membrane bounded and thus are not considered organelles |
Ribosomes in the cytoplasm translate the genetic message, carried from the DNA in the nucleus by mRNA, into a polypeptide chain. |
Centrosome
Contains a pair of centrioles |
Where the cell’s microtubules are initiated |
Chromosome
A structure within the nucleus containing one long DNA molecule |
Mitochondrion
Chemical Energy Conversion |
common to plant and animal cells |
Organelle where cellular respiration occurs |
Cellular respiration - uses oxygen to generate ATP by extracting energy from sugars, fats, and other fuels |
Nuclear Lamina
Maintains the shape of the nucleus |
Supports nuclear envelope |
Plasma membrane
Membrane enclosing the cell |
Microvilli
Projections that increase the cell’s surface area |
Cytoskeleton
Reinforces cell’s shape |
Functions in cell movement |
Components are made of protein |
It is a network of fibers that organizes structures and activities in the cell |
Includes: Microfilaments, Intermediate filaments, Microtubules |
Microfilaments
Thin rods functioning in muscle contraction |
Intermediate filaments
Support cell shape and fix organelles in place |
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In animal cells but not plant cells
Lysosomes |
Centrosomes w/ centrioles |
Flagella (present in some plant sperm) |
Eukaryotic Cell (Animal Cell)
In plant cells but not animal cells
Chloroplasts |
Central vacuole |
Cell wall |
Plasmodesmata |
Chloroplast
site of photosynthesis |
Converts energy of sunlight to chemical energy |
thylakoids - stacked like poker chips |
Capture of Light Energy |
granum - each stack of thylakoids |
Contains chlorophyll |
stroma - contains the chloroplast DNA and ribosomes |
Central vacuole
Include storage, breakdown of waste products, hydrolysis of macromolecules |
Enlargement of vacuole is a major mechanism of plant growth |
Cell wall
Outer layer that maintains cell’s shape and protects cell from mechanical damage; made of cellulose, other polysaccharides, and protein |
Plasmodesmata
Cytoplasmic channels through cell walls that connect the cytoplasms of adjacent cells |
Chromosomes
chroma - color |
soma - body |
Where DNA molecules are packaged into |
Each eukaryotic chromosome: One long, linear DNA molecule associated with many proteins |
Made of protein and a single molecule of deoxyribonucleic acid (DNA) |
Human somatic cells have 46 chromosomes, two sets of 23 inherited from each parent |
Maternal set (from your mother) Paternal set (from your father) |
Gametes (sperm and eggs): Have half as many chromosomes as somatic cells, one set of 23 in humans |
Sex Chromosomes
Determine individual's sex (X and Y chromosomes in humans) |
Females have a homologous pair of X chromosomes (XX) |
Males have one X and one Y chromosome (XY). |
Autosomes Chromosomes
Carry genetic information unrelated to sex determination |
The other 22 pairs of chromosomes |
Number of chromosomes
n |
number of chromosomes in a single set |
Diploid cell |
Two sets of chromosomes; diploid number of chromosomes (2n) |
Haploid cell |
Single chromosome set; haploid number of chromosomes (n) |
Humans: haploid number is 23 (n = 23) |
Humans: diploid number is 46 (2n = 46) |
Condensation of chromosomes
When the cell is not dividing |
Each chromosome exists as a long, thin chromatin fiber |
DNA replication occurs in preparation for cell division |
Chromosomes condense, becoming densely coiled and folded |
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Makes them shorter and thicker, visible under a light microscope |
Genome
The complete set of DNA |
A cell's endowment of DNA, its genetic information |
Prokaryotic genome |
Single DNA molecule |
Eukaryotic genomes |
Multiple DNA molecules |
Prokaryotes
Single-celled organisms lacking a nucleus and other membrane-bound organelles |
Eukaryotes
Organisms with cells that contain a nucleus and other membrane-bound organelles |
Gametes
Reproductive cells (eggs or sperm) containing half the chromosome number of somatic cells |
Gametes
Reproductive cells in plants and animals that carry genes to the next generation |
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Rudolf Virchow
German physician |
1855 |
“Where a cell exists, there must have been a preexisting cell, just as the animal arises only from an animal and the plant only from a plant.” |
Latin axiom “Omnis cellula e cellula,” |
meaning “Every cell from a cell.” |
Cell Division
The process by which a parent cell divides into two or more genetically identical daughter cells |
Involves distribution of DNA to ensure each daughter cell receives a complete set of genetic material |
Roles of Cell Division
Reproduction |
Growth and development |
Renewal and repair |
Daughter cells
The cells resulting from cell division, each containing a complete set of genetic information inherited from the parent cell |
Sister chromatids
Joined copies of the original chromosome |
Each duplicated chromosome has two sister chromatids |
Attachment known as sister chromatid cohesion |
Arms of chromatid
The portions of a chromatid on either side of the centromere |
Centromere
A region of DNA sequences where sister chromatids are closely attached. |
Mitotic (M) phase
Shortest phase |
Includes mitosis and cytokinesis |
Mitosis
The division of genetic material in the nucleus of a cell |
The nucleus divides into two daughter nuclei, each with the same number of chromosomes as the parent nucleus |
five stages of mitosis (Animal)
Prophase |
Chromatin fibers - become more tightly coiled |
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Nucleoli - disappear |
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Each duplicated chromosome appears as two identical sister chromatids |
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Mitotic spindle - Begins to form |
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Centrosomes move away from each other |
Prometaphase |
Nuclear envelope - fragments (Breaks) |
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Chromosomes - more condensed |
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Microtubules - invade the nuclear area |
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Kinetochore on microtubules |
Metaphase |
Centrosomes - opposite poles of the cell |
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Chromosomes convene at the metaphase plate |
Anaphase |
Shortest stage of mitosis |
Telophase |
Nucleoli - reappear |
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Nuclear envelopes- arise |
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chromosomes - less condensed |
Cytokinesis
The division of the cytoplasm, resulting in the formation of two daughter cells |
involves the formation of a cleavage furrow, which pinches the cell in two |
Interphase
Longer Phase (90% of the cycle) |
Cell growth, DNA replication, and preparation for cell division |
three stages: G1 phase, S phase, G2 phase |
Interphase
G1 phase |
cell growth and production of proteins and organelles |
S phase |
where DNA synthesis occurs, resulting in the duplication of chromosomes |
G2 phase |
cell continues to grow and prepares for cell division |
Meiosis
A type of cell division that reduces the chromosome number by half, occurring in reproductive cells to produce gametes |
From diploid to haploid |
Ttwo consecutive cell divisions: |
meiosis I and meiosis II |
Meiosis I
Separates homologous chromosomes |
Prophase I |
Synapsis and crossing over |
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synapsis - Replicated homologs pair up and become physically connected along their length, by synaptonemal complex, |
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Crossing over - genetic rearrangement between nonsister chromatids |
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After synapsis, two homologs pull apart slightly but remain connected by at least one Xshaped region called a chiasma (plural, chiasmata) |
metaphase I |
Alignment of homologs on the metaphase plate |
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pairs of homologous chromosomes line up on the metaphase plate |
anaphase I |
Separation of homologs |
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replicated chromosomes of each homologous pair move toward opposite poles, while the sister chromatids of each replicated chromosome remain attached |
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sister chromatids separate |
Note: |
anaphase I - cohesins are cleaved along the arms, allowing homologs to separate |
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anaphase II - cohesins are cleaved at the centromeres, allowing chromatids to separate. |
Mitosis II
Prophase II |
Spindle apparatus forms; Chromosomes, each still with two chromatids, move toward the metaphase II plate via microtubules |
Metaphase II |
Chromosomes align at the metaphase plate, similar to mitosis; Due to crossing over in meiosis I, sister chromatids are not genetically identical. - Kinetochores of sister chromatids attach to microtubules from opposite poles. |
Anaphase II |
Proteins holding sister chromatids together at the centromere break down. - Chromatids separate and move toward opposite poles as individual chromosomes. |
Telophase II and Cytokinesis |
Nuclei form, chromosomes start decondensing, and cytokinesis happens. - One parent cell's meiotic division yields four daughter cells, each with a haploid set of unduplicated chromosomes. - The four daughter cells are genetically distinct from each other and from the parent cell. |
mitosis vs meiosis
Meiosis |
Mitosis |
Halves the total number of chromosomes, reducing the number of sets of chromosomes from two (diploid) to one (haploid), with each daughter cell receiving one set |
Conserves the number of chromosome sets |
Produces cells that differ genetically from the parent cell and from each other |
Produces daughter cells that are genetically identical to the parent cell and to each other |
Binary fission
A type of asexual reproduction in prokaryotes where a cell grows and then divides into two daughter cells |
Genetics
It is the scientific study of heredity and hereditary variation |
Genes
Coded information passed from parents to offspring in the form of DNA |
Genome
Complete set of genes inherited from both parents |
Heredity
It is the transmission of traits from one generation to the next |
Gregor Mendel
He deduced the fundamental principles of genetics by breeding garden peas |
hybridization or a genetic cross
Offspring from different varieties are hybrids |
F1 generation
Hybrid offspring |
F stands for "filial," which means "son" in Latin |
Locus (plural, loci)
refers to a specific spot on a chromosome where a gene is located |
Genetics
- Genes have different forms called alleles.
- Alleles and genes can be used interchangeably.
- A gene pair refers to a set of alleles for the same gene.
- Each allele determines a specific characteristic or trait.
- Genotype refers to the combination of alleles (genetic makeup).
- Phenotype refers to observable traits, like behavior or physical appearance, resulting from the genotype.
- Homozygote for a particular allele means having two identical alleles (e.g., PP or pp).
- Heterozygote means having two different alleles for the same gene (e.g., Pp). |
Mendelian and Non-Mendelian
Mendelian:
1. Incomplete Dominance:
- Results in intermediate phenotypes.
- Example: In flowers, RR is red, rr is white, and Rr is pink.
2. Law of Independent Segregation:
- Alleles of a gene pair separate during meiosis.
- Example: In seed shape, Rr alleles segregate independently.
3. Law of Independent Assortment:
- Alleles of different gene pairs segregate independently during meiosis.
- Example: Alleles for seed color and seed shape assort independently.
Non-Mendelian:
4. Multiple Alleles:
- Many genes have more than two alleles.
- Example: ABO blood groups in humans with three alleles (IA, IB, i).
5. Codominance:
- Both alleles in a heterozygote are fully expressed.
- Example: ABO blood type where IA and IB are codominant.
6. Pleiotropy:
- One gene influences multiple traits.
- Example: A gene affecting coat color also influences eye color.
7. Polygenic Inheritance:
- Many genes contribute to one phenotype.
- Example: Skin color influenced by multiple genes.
8. Epistasis:
- One gene's expression depends on another gene's presence.
- Example: The expression of one gene (like fur color) depends on the presence of another gene (like pigment production). |
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