Bio chapter 12-14 - biology notes grade 12 PDF

Preview

Summary

biology notes grade 12...

Description

Chapter 12: The Cell Cycle 12.1 Genetically Identical Daughter Cells Cellular Organization of Genetic Material -

Every cell must duplicate genetic material (chromosomes) and other cellular constituents for replication Cells collection of genetic information is called genome DNA is packaged into chromosomes Each chromosome contains one very long linear DNA molecule associated with many proteins Cohesins: protein that attaches two sister chromatids together DNA molecules carry few thousand genes Chromatin consists of DNA and its proteins and when condensed becomes a chromosome Somatic cells carry 46 chromosomes, two sets of 23 Reproductive cells (Gametes) have one set of 23 chromosomes Each duplicated chromosome has two sister chromatids - Joined copies of original chromosome

Binary Fission -

Cell roughly doubles size, then divides and replicates Bacteria have circular DNA DNA begins to replicate on chromosomal point called origin of replication, producing two origins Replication begins when one origin moves to opposite end of cell Cell elongates when chromosome is replicating When replication is done, and cell is about 2x in size. The plasma membrane will pinch inwards and divide the two cells

12.2 Mitotic Phase Interphase -

G1 Phase - Cell grows in size and prepares for division S Phase - DNA is replicated G2 Phase - Cell continues to grow and replicates organelles - Nuclear envelope forms around nucleus - 2 centrosomes present in animal cells, helps organize the microtubules of spindle fibre - Each centrosome contains 2 centrioles - Completes new set of proteins and organelles needed for second cell

Prophase -

Chromatin condenses and chromosomes now observable Nucleoli disappears Duplicated chromosomes have 2 sister chromatids joined at centromeres Mitotic spindle begins to form Centrosomes move away from each other

Prometaphase -

Nuclear envelope fragments Microtubules extending from centrosomes can now invade nuclear area Chromosomes more condensed Each two chromatids of chromosome has kinetochore, a protein structure at centromere which allows microtubules to attach onto Nonkinetochore tubules interact with those from opposite pole of spindle

Metaphase -

Centrosomes at opposite ends of cell

-

Chromosomes aligned at metaphase plate Each chromosome has kinetochores from sister chromatids attached to kinetochore microtubules coming from opposite poles

Anaphase -

-

Shortest phase, lasts a few minutes Begins when cohesin proteins are cleaved, this allows two sister chromatids to separate - Each chromatid becomes a distinct chromosome Separase cleaves and separates two chromatids Liberated daughter chromosomes move to opposite ends of cell by kinetochore microtubules shortening Cell elongates as nonkinetochore microtubules lengthen End of anaphase, two ends of cell has equivalent and complete collections of chromosomes

Telophase -

Nucleoli reappears 2 daughter nuclei forms in cell Remaning microtubules is depolymerized

Cytokinesis -

In animal cells, cleavage furrow forms and pinches 2 cells apart Cytoplasm divides and two new cells are formed In plant cells there is no cleavage furrow Vesicles made from golgi apparatus during telophase will move to middle of cell along microtubules, producing cell plate Cell plate will enlarge and fuse its membrane with plasma membrane

Mitotic Spindle -

Spindle fibre forms during prophase, consists of microtubules and associated proteins Microtubules elongates by incorporating more units of tubulin and shortens by removing tubulin Microtubules attaches to kinetochore of chromosome and pulls towards pole of cell Kinetochores contain motor proteins that shorten at kinetochore end, not spindle end. Requires ATP Chromosome walks along microtubule and depolymerizes

12.3 Regulation of Eukaryotic Cell Cycle -

Cell cycle is driven by signalling molecules present in cytoplasm Cell cycle control system contains multiple checkpoints that needed to be passed for cell to continue through division 3 main checkpoints - G1 checkpoint, G2 checkpoint, M checkpoint

Cell Cycle Control System -

-

-

Regulated by two main protein molecules - Protein kinases and cyclins Protein kinases activate/deactivate other proteins by phosphorylating Kinase is only active when binded to cyclin, thus it is called a cyclin-dependent kinase or Cdk Activity of Cdk is dependent on concentration of cyclin Concentration of cyclin follows same peak activity patterns as MPF (Maturation Promoting Factor) - Cyclin level rises during S and G2 phase, falls in M phase

MPF triggers cell to pass checkpoint in G2 to M phase During G2 when cyclin associates with Cdk, MPF is produced. The MPF complex will phosphorylate proteins and initiating mitosis - MPF activity peaks during metaphase MPF cyclin component degraded during anaphase, terminates M phase and cell enters G1 During G1, degradation of cyclin continues and Cdk component of MPF is recycled

Checkpoints -

A checkpoint is a control point where stop/go signals regulate cycle G1 checkpoint usually dictates if cell will go through all the other checkpoints, therefore a go signal in G1 is important If no go then it will reach G0 - Cells do not divide. Many cells actually in G0 such as muscle cells M phase checkpoint - Anaphase doesn’t begin until all chromosomes properly attached - Cell in mitosis reaches stop signal when any chromosome is not attached to spindle fibre - Once activated checkpoint, separase will cleave the cohesins

Growth Factors -

Growth factors are proteins that stimulates other cells to divide Cells need required nutrients for division, growth factors provide proteins and stimulate other cells to divide

Platelet Derived Growth Factor -

PDGF are blood cell fragments and is a type of connective tissue Triggers signal transfuction pathway that allow cells to pass G1 checkpoint and divide Density dependent inhibition will stop it from dividing uncontrollably - When cell borders are crowded, cell division stops

Loss of Cell Cycle Controls in Cancer Cells -

Uncontrolled cell division causes cancer Cancer cells divide as long as nutrients are present and ignore apoptosis signals Tumors are forms of clumps of cancer cells - Benign tumor is when cancer cell remains in singular area and can be surgically removed - Can also be treated with high energy radiation which damages DNA in cancer cells but not normal cells - Malignant tumor is when cell can spread to other areas in body, such as tissues - Impedes organ functions

Chapter 13: Meiosis -

Diploid: cell contains two sets of chromosomes Haploid: cell containing one set of chromosomes

13.1 Stages of Meiosis Types of Reproduction -

-

Asexual - Production of offspring that is genetically identical to single parent, doesn’t require other individual for mating Sexual - Produces genetically unique offspring, fusion of gametes

Prophase 1 -

-

Occurs for 90% of total time Synapsis: homologous chromosomes pair up and align gene by gene. Synaptonemal complex holds it together - Homologous: same numbered chromosome, positions of genes are the same however can contain different alleles Crossing over occurs at point called chiasmata Microtubules attach to 2 kinetochores, one in each centromere of homologous chromosome

Metaphase 1 -

Tetrads line up on metaphase plate Both chromatids of homologue are attached to kinetochore microtubules in one pole and the other homologue has chromatids attached to kinetochore microtubules in other pole

Anaphase 1 -

Pair of homologous chromosomes are separated by microtubule depolymerization

Telophase 1 -

Two haploid cells formed Sister chromatids are attached to each other still in the chromosome

Meiosis II

13.2 Crossing Over and Synapsis Crossing Over and Synapsis -

-

After interphase, sister chromatids are held together by cohesins - These proteins are removed in metaphase (mitosis), metaphase 2 in (meiosis) After two chromosomes are crossed over, the DNA is broken at the same point along the chromatid Synaptonemal complex holds the homologues tightly together When DNA breaks are closed up and joined to corresponding segment, this is called synapsis

13.3 Meiosis vs Mitosis Mitosis (both diploid/haploid cells)

Meiosis (only diploid)

DNA rep. is in Interphase

DNA rep. is in Interphase

1 division

2 divisions

Synapsis doesn’t occur

Synapsis in prophase I

Produces 2 diploid cells, exact copy of parent

Produces 4 haploid cells, genetically varied

Produces cells for growth, repair and in some species asexual reproduction; produces gametes in gametophyte plant

Produces gametes in animals, spores in sporophyte plant. Also reduces # of chromosomes in half

13.4 Genetic Variation and Evolution Origins of Genetic Variation -

3 mechanisms contribute to genetic variation - Independent Assortment - Crossing Over - Random Fertilization

Independent Assortment of Chromosomes -

During metaphase 1, each chromosome is aligned on plate Each pair may orient with its maternal or paternal Each pair is independently oriented 50% chance daughter cell will get maternal and 50% daughter cell will get paternal chromosome when cell splits Total chromosome combination is 2n, n = # chromosomes

Genetic Variation in Crossing Over -

Produces recombinant chromosomes - Recombinant chromosomes: individual chromosomes that carry DNA from both parents

Random Fertilization -

Refers to the probability of fertilizing one sperm with one egg to produce a zygote 70 trillion combinations of zygotes from both male and female gametes

Genetic Variation in Chromosome Number -

-

-

Polyploid: organisms with more than two complete sets of chromosomes - Triploidy (3n), tetraploidy (4n) Nondisjuction: error in separation of chromosomes or chromatids in meiosis - Causes aneuploidy, irregular number of chromosomes in one of the gametes Monosomic Zygote: one copy of particular chromosome Trisomic Zygote: three copies of particular chromosome

Nondisjuction -

Breakage of spindle fibres causes abnormal chromosome count in daughter cells, this can cause diseases in offspring Down Syndrome - Trisomy 21: three copies of 21 chromosome Klinefelters Syndrome - result of extra X chromosome in males, producing XXY Turner’s Syndrome - Monosomy X : produces X0 females, making them sterile

Chapter 14: Mendel and Gene Idea Terms -

True Breeding: producing same variety type offspring Hybridization: crossing two true breeding varieties P Generation: true-breeding parents F1 Generation: offspring of P generation F2 Generation: offspring of F1 generation Character: heritable feature Trait: variant for a character, such as pink flowers

14.1 Two Laws of Inheritance Inheritance and Genes -

Alternate genes account for variation in characters Alternative versions of genes are called alleles Each gene resides on specific part of locus on specific chromosome Organism inherits two alleles, one from each parent

Mendelian Inheritance -

Dominant Allele: determines organisms appearance Phenotype: observable characteristics of organism Genotype: set of two alleles for a specific gene, based on this a phenotype is expressed Recessive Allele: recessive gene will not be expressed Homozygous: two of the same alleles, can be either homozygous dominant or homozygous recessive Heterozygous: one dominant and one recessive allele

Law of Segregation -

Allele pairs for a character segregate during gamete formation and end up in different gametes Therefore during fertilization, only one allele is from one parent for that character, and the other character is gained by the other parent Occurs during anaphase 2 of meiosis

Law of Independent Assortment -

-

The way an allele pair gets separated into two daughter cells in meiosis, has no effect on how other alleles get separated. This is because genes reside on different chromosomes. Occurs during metaphase 1 because chromosomes are lined up in random assortment Mendel formulated this principle after performing dihybrid crosses, between plants that differed in two traits - Dihybrid Crosses: mating between two organisms that are identically hybrid in two traits, two heterozygous traits

14.3 Predicting Inheritance Patterns with Simple Mendelian Genetics Degrees of Dominance -

Complete dominance: one allele completely masks the other and shows its phenotype Incomplete dominance: where the recessive trait is also showing and the dominant trait doesn’t completely mask Codominance: two alleles affect phenotype in separate, distinguishable ways

Multiple Alleles -

More than two allelic forms Ex. ABO blood group, the group can be A, B or O - Three alleles for the one enzyme that attaches to A or B carbohydrates

Polygenic Inheritance -

Additive effect of two or more genes on a single phenotype Skin colour and height are quantitative characters, therefore the more additive effect on them the darker/taller the character will become

14.4 Disorders Recessively Inherited Disorders -

-

When the recessive allele (a) codes for a malfunctioning protein or no protein at all In heterozygous (Aa), this is normal because the dominant A will provide sufficient protein - Will however be a carrier for the lethal “a” allele still But in homozygous recessive (aa), this will cause disorder

Cystic Fibrosis -

Normal allele will code for a protein to transport Cl- ions between certain cells and ECF In homozygous recessive “aa”, where “a” is malfunctioning Protein will not function well and therefore cause high concentrations of ClThis causes mucus that coats certain cells to thicken in pancreas, lungs, digestive tracts, and other organs Build up of this causes poor absorption of nutrients, bronchitis and recurrent bacterial infections

Sickle Cell Disease -

Caused by substitution of single amino acid in hemoglobin protein Sickle cells carry less oxygen and are prone to clumping Presence of one sickle cell allele can affect an individual - Incomplete dominant allele, therefore has sickle allele has effect Homozygous recessive individuals have all hemoglobin abnormal - Suffer physical weakness, pain, organ damage, and even paralysis

Dominantly Inherited Disorders -

-

Dominant alleles cause disorder Achondroplasia - Dwarfism, this is caused by rare dominant allele, heterozygous individuals have this - Homozygous recessive individuals account for the majority of this genotype Huntington’s Disease - Degenerative nervous system disease that has no phenotypic effects until an individual is 35-40 - Once disease begins, it is fatal - Note: this is an exception, most dominant alleles that are lethal are usually very rare and die before reproduction and often arise by mutation

Genes and Environment -

-

Some genes are silenced or stamped with an imprint during gamete production - May be result of methylation of DNA Diseases such as diabetes, heart disease, alcoholism, mental illness, and cancer have both genetic and enviromental components Overall phenotype depends on physical appearance, internal anatomy, physiology and behaviour...