Biology Unit One Quiz #1 Review

Chromosome

Chromosome

A single piece of coiled DNA containing many genes.

How do Chromosomes Form

A single length of DNA is wrapped many times around histones, and forms nucleosomes. Nucleosomes then coil up tightly to create chromatin loops. Chromatin loops are then wrapped around each other to form a ____________.

Diploid

Having a pair of each type of chromosome. This means that one pair is derived from the ovum and the other from the sperm.

Haploid

Having only one copy of every chromosome. This is where n= 23.

Genes

Basic unit of heredity in a living organism. ______

hold information to build and maintain an organism’s cells and pass traits to offspring.

What is A Gene

A segment of a chromosome that contains the code for a single protein (enzyme). The enzyme then causes a chemical reaction to allow a trait to be shown/expressed.

Allele

Variation of a gene located at a specific location on a chromosome. Each individual organism has two ______ for each trait, which may be homozygous or heterozygous. _______ are alternate forms of a gene.

Homologous Chromosomes

It is chromosomes that are paired. They are alike with regard to size and also position of the centromere. They also have the same genes, but not necessarily the same alleles, at the same locus or location.

Tetrad

Pair of homologous chromosomes. Chromatids of homologous chromosomes are aligned lengthwise, so that genes of one are adjacent to corresponding genes on the other (total of 4 chromatids).

Synapsis

The forming of a tetrad.

Gamete

Specialized sex cells such as an egg or a sperm, which is haploid (n). It only has half the number of chromosomes (23 in humans). A male and female gamete fuse and produce a diploid zygote which develops into a new individual.

Inheritance

Passing on genetic information from parent to offspring.

Sex Chromosomes

It is 1 pair out of 23, where it is called X and Y, determining individual’s sex (Female= XX, Male= XY).

Autosomes/Somatic Chromosomes

It is 22 pairs out of 23, where it is all chromosomes but sex cells, and it is paired based on similar characteristics.

Karyotype

A photograph of a particular set of chromosomes for an individual. In order to prepare a karyotype, you sample a cell in metaphase, have the chromosomes stained, revealing banding patterns, and then sort and pair afterwards.

DNA

Contains instructions for making proteins within the cell.

Double Helix

Basic shape of DNA, a double-stranded molecule made of two very long polymers bonded together.

Polymer

Long molecule made of repeating subunits of monomers (one DNA strand is made of millions of monomers of nucleotides).

Monomer

Atoms bonded together to create a larger molecule, many __________ bond together to create various polymers (nucleotides are _________ of DNA).

Nucleotides

Basic building blocks of DNA & RNA.

Parts of Nucleotides

Deoxyribose pentose sugar, phosphate group & nitrogenous base.

Deoxyribose

Sugar in DNA.

Ribose

Sugar in RNA that has an additional oxygen as a hydroxyl group in #2 carbon.

Phosphate group

Link two sugars together to build polymers.

Phosphodiester Bond

Joins two sugars via phosphate vertically (joins two nucleotides).

Condensation Reaction

Produces H20 when phosphodiester bonds form.

Nitrogenous Bases

Four different nucleotides that make up a DNA polymer.

Purine Deoxyribonucleotides

Guanine & Adenine (have 2 rings).

Pyrimidine Deoxyribonucleotides

Thymine & Cytosine (have 1 ring).

Uracil

Takes the place of thymine in RNA.

The Backbone

One strand of DNA made of repeating monomers covalently bonded together.

Triplet Code

Used to send instructions in the cell:to switch genes on and off to make proteins and enzymes.

Hydrogen Bond

Holds DNA strands together and is weaker than molecular bonds. Millions in a single molecule cause bases to attract each other.

Complementary Base Pairs

Only bond with each other (A&T or U) (C&G).

Antiparallel

one side up and the other down (in DNA the direction of phosphate (5’end) on one stand and the hydroxyl (OH 3’end) on the other)

DNA Relpications

process where an original copy of DNA is unzipped and replicated producing two new identical molecules of DNA.

Why DNA Replicates

as a cell’s chromosomes are copied for cell division, DNA must be copied too, since DNA makes up chromosome. Instructions for making cell parts are encoded in the DNA so each new cell must get a complete set of the DNA molecules.

Unwinding of Double Helix

used in DNA replication, where each strand of DNA becomes a new template for a new strand. Each double stranded DNA contains the original copy and one new strand. Parent DNA molecule and two daughter molecules are identical (same nucleotides in same order) 

Helicase

The enzyme (protein) that breaks the hydrogen bonds between nitrogenous bases to “unzip” or “unwind” the DNA helix. This is the first step in DNA replication.

DNA Polymerase

 An enzyme that moves along the single strands of DNA and helps each free nucleotide bind to a new complementary base to form base pairs. This is the second step to DNA replication and happens as the DNA unzips. 

Semi-conservative Model of Replication

one daughter strand is paired with a parent strand, one old one new is semi-conservative

Why new cells are produced

for growth and to replace damaged or old cells, all cells are derived from pre-existing cells

Prokaryotes

organisms whose cells lack a nucleus and other organelles, for ex. bacteria

Eukaryotes

organisms whose cells contain membrane-bound organelles for ex. Animals 

Eukaryotic Chromosomes

store genetic information, have between 10-50 chromosomes in their body cells, human body cells have 46 chromosomes (23 pairs)

Chromatin

long uncoiled strand of DNA that takes up less space in a cell. They can’t be seen when cells aren’t dividing.

Histones

a protein which DNA is tightly coiled around to form structures call nucleosomes. Makes mixed up DNA strands into sticks/chromatin

Chromatid

Duplicated chromosomes which aren’t held together by the centromere

Centromere

holds sister chromatids together

Asexual Reproduction

a single cell dividing to make 2, identical daughter cells

Sexual Reproduction

involves two cells (egg & sperm) joining to make a new cell (zygote) that is not identical to the original cells

5 Phases of Cell Cycle

Interphase (G1 - primary growth, phase) (S synthesis; DNA replicated) (G2 - secondary growth phase), Mitosis, Cytokinesis

Interphase (G1)

1st growth stage after cell division, Cells mature by making more cytoplasm & organelles, so daughter cells have all organelles, Cell carries on its normal metabolic processes

Interphase (S stage/synthesis)

DNA is copied or replicated

Interphase (G2)

2nd growth stage, occurs after DNA has been copied, all cell structures needed for division are made (ex. Centrioles which move to poles), both organelles & proteins are synthesized

Mitosis/Karyokinesis

Division of the nucleus, only occurs in eukaryotes, has 4 stages, doesn’t occur in some specialized cells such as brain cells

Early Prophase

Chromatin in nucleus condenses to form visible chromosomes (creates absence of space in nucleus), Mitotic spindle forms from fibers in cytoskeleton or centrioles (animal)

Late Prophase

Nuclear membrane & nucleolus are broken down, chromosomes continue condensing & are clearly visible, spindle fibers called kinetochores attach to the centromere of each chromosome (Only called kinetochores only if they grab the centromere of the chromosome called the astor if it doesn't) Spindle finished forming between the poles of the cell 

Metaphase

Chromosomes, attached to the kinetochore fibers, move to the center of the cell, chromosomes are now lined up at the equator (or _________ plate), preparing for the actual division of the chromosomes

Anaphase

Occurs rapidly, high forced, sister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers 

Telophase

Sister chromatids at opposite poles, Spindle disassembles (disappears), Nuclear envelope (nuclear membrane) forms around each set of sister chromatids, Nucleolus reappears, Cytokinesis occurs, Chromosomes reappear as chromatin

Cytokinesis

division of the cytoplasm, Division of the cell into half, in plant cells, cell plate forms at equator to divide cell, In animal cells, cleavage furrow forms to split cell 

Daughter Cells of Mitosis

Have the same number of chromosomes as each other and as the parent cell from which they were formed, Identical to each other, but smaller than parent cell, Must grow in size to become mature cells (G1 of Interphase)

Checkpoints in the Cell Cycle

messages sent to the cells nucleus to “divide, or not to divide” at: G1, S Synthesis phase (DNA Replication): cyclins/cyclin dependent kinase signals the division, G2 gap phase 2- cell size/energy reserves are assessed and if all chromosomes have been replicated correctly, M checkpoint (metaphase): spindle checkpoint, are the sister chromatids attached correctly 

Meiosis

occurs after interphase to form gametes, starts with 46 double-stranded chromosomes which is 23 pairs of homologous chromosomes. Is called a reduction - division. The original cell is diploid (2n) 4 daughter cells are produced that are haploid (1n)

Meiosis I

homologous chromosomes separate, 23 double stranded chromosomes after division

Meiosis 2

sister chromatids separate (end up with 4 haploid cells), 23 single stranded chromosomes after division

Spermatogenesis

the meiosis process which occurs in the testes in males to produce sperm cells 

Oogenesis

the meiosis process which occurs in the ovaries in females to produce egg cells

Zygote

a fertilized egg cell - when two haploid (1n) gametes (sperm and egg cell) fuse to form a diploid (2n) zygote. 23 chromosomes from father, 23 from mother 

Crossing over

homologous chromosomes in a tetrad cross over each other, pieces of chromosomes are exchanged, produces genetic recombination in the offspring which increases genetic diversity 

Law of Independent Assortment

there can be a mix of maternal & paternal chromosomes on either side of the equator in Metaphase I 

Early Prophase I

chromosomes number doubled, forms homolog pairs 

Late Prophase I

the chromosomes condense, crossing over occurs, spindle fibers form, and the nuclear envelope fragments

Metaphase I

homologous pairs of chromosomes align along the equator of the cell, so there are two rows of chromosomes. centromeres are at the opposite sides of the cells, and this is where the mitrotubules attach to the centromere/kinetochore

Anaphase I

homologs separate and move to opposite poles, sister chromatids remain attached at their centromeres. Each copy of chromosomes are on separate sides of the cell. They are not entirely identical, as it’s composed of different characteristics (from paternal or maternal one can have more than the other)

Telophase I

the nuclear envelopes reassemble, spindle disappears, and it now divides the cell into two, as the cells are now haploid

Cytokinesis I/Interkinesis

chromosomes completely uncoil to become chromatin, nuclear membrane completely reforms 

Meiosis II

only one homolog of each of the chromosome is present in the cell, and the sister chromatids carry identical genetic information

Interphase II

the cells prepare for division, chromatin begins to coil/condense into chromosomes, however the DNA is not duplicated so it remains a haploid (n)

Prophase II

the nuclear envelope fragments, chromosomes condense, the spindle forms, however there is no crossing over

Metaphase II

chromosomes line up at the center of the cell (no longer in pairs through), independent assortment occurs again of the sister chromatids, and the microtubules attach to the centromere/kinetochore

Anaphase II

the sister chromatids separate and now move to opposite poles of the cell, and continue to be haploid

Telophase II

the nuclear envelope assembles, chromosomes now uncoil, spindle disappears, and now cytokinesis occurs by dividing the cell into two. There is now 4 haploid daughter cells. 

Cytokinesis II

produces 4 haploid daughter cells

Results of Meiosis

the gametes (egg & sperm) form, as four of the haploid cells contain one copy of each chromosome. there is one allele for each gene, and it contains different combinations of alleles for different genes along the chromosome