Bio 120 Exam 3

haploid cells

one set of chromosomes (23); gametes

diploid cells

2 sets of chromosomes (46); somatic (body) cells

How do chromosomes get replicated

each chromosome creates a duplicate, forming sister chromatids connected together by a centromere

G1 Interphase

The cell doubles organelles and grows

G1 checkpoint

Checks to see if DNA is damaged

Apoptosis

if DNA can’t be repaired by the p53 tumor-suppressor gene and is unfixable; cell death

S phase of interphase

DNA/centrosome replication

G2 interphase

Cell prepares to divide by preparing microtubules and spindles; cytoskeleton dismantles to provide resources for the miotic spindle; nuclear envelope and nucleolus are intact; duplicated DNA as chromatin as well as duplicated centrosomes

G2 checkpoint

Allows to check if DNA is replicated correctly before starting mitosis

Mitotic spindle

Made up of microtubules that can lengthen; organized by a centrosome

Sister chromatids

each contain identical DNA double helix (the DNA that was duplicated); held together by a centromere

centromere

the region of a chromosome to which the microtubules of the spindle attach

Mitosis prophase

Inside the nucleus duplicated chromatin (DNA and proteins) condenses into chromosomes made up of sister chromatids held by a centromere; outside the nucleus centrosomes begin separating and grow microtubules and spindle; the nuclear membrane and nucleolus disintegrate; Golgi and ER fragment and move to the cell periphery; spindle fibres from each centrosome attach to either side of a centromere; centrosomes move to opposite sides of the cell; chromosomes start moving toward the center of the cell

Mitosis metaphase

Chromosomes with spindle fibres attached to centromere line up in the middle equator of the cell in order to later separate the sister chromatids

Mitosis checkpoint

Mitosis stops until chromosomes are properly aligned

Mitosis anaphase

Sister chromatids are drawn apart by shortening (disassembling) spindle fibres, becoming separate daughter chromosomes

Mitosis telophase

Chromosomes reach the poles; spindle disappears and nuclear envelope reforms around daughter chromosomes; Each nucleus now contains the same number and kinds of chromosomes as the original parent cell (two identical daughter cells form one parent cell) and each daughter cell is genetically identical; Cytoplasm begins to divide (cytokinesis)

Cytokinesis (in animal cells)

Cleavage furrow (indentation) forms between two daughter nuclei; A contractile ring made of actin filaments begins to pinch off the two forming daughter cells

Stages of cell cycle

G1 interphase

G1 checkpoint

S phase

G2 interphase

G2 checkpoint

M prophase

M metaphase

M checkpoint

M anaphase

M telophase

Cytokinesis

Mitosis

results in 2 identical diploid cells, involves one round of division; a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus;

Cancer

uncontrolled cell growth caused by mutations in genes that regulate the cell cycle. It gets bad because they blow past the checkpoints so the genes that progress through the cell cycle have mutations. It progresses as cells become increasingly abnormal and lose the ability to respond to normal growth signals

Contact inhibition

process where cells stop growing when they come into contact with other cells. Cancer cells do not exhibit this function and continue to grow uncontrollably

Metastasis

Spread of cancer cells to other parts of the body, which is dangerous because it can lead to the formation of secondary tumors and complicate treatment

Meiosis

results in 4 non-identical haploid cells (gametes), involves two rounds of division

Homologous chromosomes

pairs of chromosomes, one form each parent, that are similar in shape, size, and genetic content. They are crucial in meiosis for ensuring genetic diversity

Purpose of meiosis

To produce haploid gametes for sexual reproduction, ensuring genetic diversity through recombination and independent assortment

Recombination

the process where two DNA molecules exchange genetic material, resulting in new combinations of alleles and increasing genetic diversity

Independent assortment

a genetic principle that states that different genes are inherited independently of one another. This means that the allele a cell receives for one gene is not influenced by the allele it receives for another gene

Oogenesis

production of eggs; Starts with an Oocyte that divides unequally because the biggest one is the only one that is useful and the others (polar bodies) are discarded; results in one functional egg

Spermatogenesis

production of sperm; start with spermatocyte that undergoes meiosis and divides resulting in four functional sperm cells that are equal in size

Why do gametes have to be haploid

to ensure that when fertilization occurs, the resulting zygote will have a diploid set of chromosomes

Steps of meiosis

Prophase 1

Metaphase 1

Anaphase 1

Telophase 1

Interkinesis

Prophase 2

Metaphase 2

Anaphase 2

Telophase 2

Prophase 1

Crossing over between non sister chromatids because they’re touching during synapsis; homologous chromosomes exchange genetic material

Metaphase 1

Homologous chromosome pairs (tetrads) align at the metaphase plate (equator); duplicated homologous next to each other as tetrads (facing opposite poles)

Tetrad

the structure formed by a pair of homologous chromosomes, each consisting of two sister chromatids, during prophase I, allowing for crossing over and genetic recombination

Anaphase 1

Homologous chromosomes of each tetrads separate; dyads (centromeres intact) move to opposite poles; the daughter cells are haploid

Telophase 1

The separated homologous chromosomes (each consisting of two sister chromatids) reach the opposite poles of the cell; Nuclei reappear; the two daughter cells will be haploid because there’s only one set of chromosomes but have two sister chromatids

Interkinesis

Interphase between meiosis 1 and meiosis 2; no DNA replication

Prophase 2

Chromosomes condense again in both daughter cells, and a new spindle forms; no homologous pairing of chromosomes or crossing over

Metaphase 2

Individual chromosomes (sister chromatids) line up at the metaphase plate and spindle fibers attach to the centromeres. This time they’re not touching and are positioned on top of eachother

Anaphase 2

Sister chromatids pull apart and separate to the opposite poles of the cell

Telophase 2

The chromosomes (now single chromatids) reach the poles and the cells divide resulting in 4 haploid daughter cells

Down syndrome

Trisomy 21

Turner syndrome

Monosomy 45 45 45 45 45 45 45 45 45 45 45 45 45 45 45 45 45 45 45 45; it occurs when a female is missing one or part of an X chromosome, which is one of the sex chromosomes

Klinefelter syndrome

EXTRA EXTRA EXTRA EXTRA EXTRA EXTRA EXTRA EXTRA EXTRA a genetic condition that affects males, resulting in an extra X chromosome (47,XXY instead of the typical 46,XY)

Maleness in embryonic development

when the SRY gene on the Y chromosome triggers the formation of testes and the secretion of male hormones (testosterone) starting around week 7 of development.

Gregor Mendel

Scientist who established the basic principles of heredity using pea plants, discovering laws of inheritance

Mendel’s laws

traits are controlled by a single pair of alleles, they are on autosomal chromosomes (not sex chromosomes), Can be tracked through a pedigree

Pedigree

A chart of a family's history with regards to a single genetic trait; Males are squares, females are circles, horizontal lines are union, vertical line leads to offspring, shaded square/circle individuals express trait

Law of dominance

Dominant traits override recessive traits

Law of segregation

During meiosis, the two alleles for each gene separate so that each gamete carries only one allele for each gene; one copy of each gene in each gamete

Law of independent assortment

All possible combinations of factors can occur in the gametes; Different combinations because of how the chromosomes line up during metaphase 1

True breeding

If they self pollinate the babies have the same trait as the parent; Mendel used these plants to ensure purebred traits for his genetic experiments (HOMOZYGOUS SYNONYM)

Mendel’s ratio in monohybrid crosses

(hybrid for one trait) produced a 3:1 ratio of dominant to recessive traits in the F2 generation. (HETEROZYOUS SYNONYM)

Why do traits “disappear”

due to dominant and recessive allele interactions, with the recessive trait not being expressed unless both alleles are recessive. (in f1 generations)

Allele

Variant form of a gene; found at specific loci on chromosomes

Locus

Where genes are located on chromosomes; address; not at the end

Dominant traits

Only one copy of the allele is needed to express the trait

Recessive traits

Two copies of the allele (homozygous) are needed for the trait to be expressed

Homozygous

Both alleles are the same

Heterozygous

two different alleles

Punnett square

a visual tool used in genetics to predict the possible genotypes and phenotypes of offspring from a cross between two parents, by showing all possible combinations of their alleles

Incomplete dominance

BLEND; neither allele for a trait is fully dominant, resulting in a heterozygous phenotype that is a blend or intermediate between the two homozygous phenotypes

Co-dominance

TWO DIFFERENT COLORED EYES; a type of inheritance in which two versions (alleles) of the same gene are expressed separately to yield different traits in an individual

Multifactorial inheritance

a pattern of inheritance where a trait or disease is influenced by multiple factors including genes and environmental factors

Polygenic inheritance

involves multiple genes influencing a single trait (POLY)

Pleiotropy

when one gene affects multiple traits (genetic disorders cause multiple sympotms)

Why are males more affected by x-linked traits

Males are more affected because they have only one X chromosome while females have two

Mutations

Changes in the DNA sequence that can result in altered proteins. They can be caused by environmental factors or errors during replication; changes to the structure or number of chromosomes (deletions, duplications, inversions, translocations)

Under what conditions can traits fail to assort independently

when genes are located close together on the same chromosome which leads to genetic linkage

Silent mutation

A mutation that does not change the protein due to the redundancy of the genetic code

Point mutation

are those mutations that affect a single base pair

Frameshift mutation

Occurs when nucleotides are added or deleted, shifting the reading frame and often resulting in a nonfunctional protein

Why are mutations uncommon

because of DNA repair mechanisms and the proofreading ability of DNA polymerases

Non-disjunction

failure of chromosomes to separate properly

Cri-du-chat syndrome

a deletion of part of chromosome 5 caused by a mutation not an extra chromosome

DNA arrangement

organized into chromosomes in the cells nucleus; in eukaryotes its wrapped around histones to form chromatin

Chargaff’s rules

A-T C-G

Rosalind Franklin

X-ray diffraction images of DNA helped reveal its helical structure, providing key evidence for Watson and Crick’s DNA model

Evidence for DNA structure

Chargaff - Chemical analyses

Franklin - X-ray crystallography

Watson/Crick - Model building

Helicase

R1 Unwinds DNA

Primase

R2 priming; adds primers

DNA polymerase

R3 Elongation adds nucleotides but can also backspace wrong ones and is the first place DNA can get repaired

Sequence of DNA replication

Unwinding of DNA by helicase

Priming by primase

Elongation by DNA polymerase

Joining of fragments by ligase

Viruses

infectious agents composed of genetic material (DNA or RNA) encased in a protein coat. They reproduce by hijacking host cell machinery

Lytic cycle of bacteriophage

Involves the integration of viral DNA into the host genome

Attachment, entry, replication, assembly and lysis; The virus keeps spreading and materializes

Animal virus reproduction

enter the host cell, replicate and assemble new virions, often by budding off the host cell

Virion

The complete, infective form of a virus outside a host cell, with a core of RNA or DNA and a capsid

RNA nitrogenous base

Uracil replaces thymine

Transcription

the synthesis of mRNA from DNA

Translation

synthesis of proteins from mRNA

mRNA (messenger)

carries the genetic code from DNA to the ribosomes, where proteins are synthesized; provides the blueprint for protein synthesis, which each three nucleotide sequence (codon) specifying particular amino acid

rRNA

Acts as a ribozyme (RNA enzyme) that catalyzes the formation of peptide bonds between amino acids

tRNA (transfer RNA)

Recognize mRNA codons and deliver the corresponding amino acids to the ribosome, ensuring the correct sequence of amino aids in the newly synthesized protein; act as adaptors, bringing specific amino acids to the ribosome to be incorporated into the growing polypeptide chain during protein synthesis

Central dogma

DNA to RNA to Protein

Stages of translation

Initiation - The ribosome assembles around the mRNA molecule, specifically at the start codon (AUG), and the first tRNA (carrying methionine) binds to the start codon

Elongation - The ribosome moves along the mRNA, reading each codon and adding the corresponding amino acid to the growing polypeptide chain. tRNAs bring the appropriate amino acids, and peptide bonds form between them

Termination - The ribosome encounters a stop codon (UAA, UAG, or UGA), signaling the end of translation. The polypeptide chain is released, and the ribosome disassembles

Codons

Specify amino acids on mRNA

anticodons

help match the correct tRNA to the mRNA codon

Biotechnology

involves using living organisms or their products for industrial or medical purposes

Gel electrophoresis

separates DNA or proteins by size using an electric field; since nucleic acids are negatively charged at neutral and basic pH in a watery environment, they can be mobilized by an electric field