Biology Exam 8-12

Asexual Reproduction

creation of genetically identical offspring by a sing parent (no eggs and sperm)

Produce offspring that are genetic copies of the parent and identical to each other (clones)

Sexual Reproduction

reproduction that requires the fusion of gametes (sperm and eggs)

Cell Division

proceeds daughter cells or gametes

cells originate only from preexisting cells

each species carries its own specific genetic information

* Cell division involves the separation of sister chromatids and results in two daughter cells, each containing a complete and identical set of chromosomes.

Binary Fission

prokaryotic cells reproduce asexually, binary fission means dividing in half

Contrast the structure and number of prokaryotic and eukaryotic chromosomes

In Prokaryotes, most genes are carries on one circular DNA molecule, with associated proteins constitutes the organisms SINGLE CHROMOSOME

* as the cell relocated the one chromosome
* the copies move apart
* the plasma membrane pieces inward and more cell wall is made, which divides the parent cell into two daughter cells

In Eukaryotes, there are many more genes than prokaryotic cell, and they are grouped into MULTIPLE CHROMOSOMES in the nucleus

* Each eukaryotic chromosome contains one long D N A molecule.


* Individual chromosomes are visible under a light microscope only when the cell is in the process of dividing; otherwise, chromosomes are thin, loosely packed **chromatin** fibers too small to be seen

Cell Cycle

interphase + mitotic phase (mitosis + cytokinesis)

Mitosis

Division of nucleus into two identical nuclei

Cytokinesis

Division of the cytoplasm immediately after mitosis

Sister Chromatids

Contains identical DNA

* before cells start dividing, the chromosomes duplicate producing sister chromatids
* DNA after it has duplicated and has two identical copies (connected most closely at the centromere) The

Chromosomes

DNA structures that carry a cell’s genetic information and are found in the nucleus of eukaryotic cells

Chromatin

DNA (and its associated proteins) in a diffuse, stretched-out form when a cell is not dividing and cannot be seen in a light microscope 

The Cell Cycle

is an ordered sequence of events that run from the time a cell is first formed from a dividing parent cell until its own division into two cells

Interphase

cell grows, has high metabolic activity, synthesizes organelles, and performs its normal function. __Includes G1 + S + G2 phases__

G1

growth and metabolism (DNA in chromatin form)

Synthesis

duplication/replication of DNA (still in chromatin form)

G2 Phase

preparation for cell division (sister chromatids in chromatin form)

Mitosis

distributes duplicated chromosomes into two daughter nuclei (mitosis = division of __nucleus__)

Mitotic Spindle

made up of microtubules, moves the chromosomes to the middle of the cell

Prophase

chromosomes condense and spindle forms

Double

Pro metaphase

nuclear membranes breaks down and microtubules reach each the chromosomes

* single

Metaphase

spindle complete and chromosome lines up in the middle

* Double

Anaphase

sister chromatids separate and move to opposite poles of the cell

* single

Telophase and Cytokinesis

nuclear envelope forms, chromatin uncoils, cleavage furrow forms

* Double

Contrast cytokinesis in plant and animal cells

In animals

* cytokinesis occurs when a cell constricts, forming a cleavage furrow


* Contracting microfilaments pinch the cell in two like a drawstring 

In plants

* a membranous cell plate forms and then split the cell in two
* vesicles collect in the center and fuse

Growth Factor

a protein that stimulates cells to divide

What is Cancer?

a disease of the cell cycle

* the cells divide excessively to form masses called tumors. They do not need cell cycles

Benign Tumor

the abnormal cells remain at the original site

Malignant Tumor

the abnormal cells spread to nearby tissues and invade other parts of the body. This is **cancer** and the spread of cancer cells beyond the original site is **metastasis**

Moisis

the division of a single diploid nucleus unto four haploid nuclei (gametes)

Homologous Pairs

* The **somatic** (body) **cells** of each species contain a specific number of chromosomes; for example, human cells have 46, consisting of 23 pairs of **homologous chromosomes** - one inherited from your mother, one from your father

Homologous Chromosomes

one inherited from your mother, one from your father

Diploid Cells

Cells with two sets of homologous chromosomes (46 chromosomes in humans (one from each parent)

Gametes

eggs and sperm, are haploid cells with a single set of chromosomes (23 chromosomes)

Meiosis

chromosome duplication, but the cell DIVIDES TWICE to four four daughter cells (gametes)

Crossing Over

homologous chromosomes exchange corresponding segments

In Meiosis I

the haploid cells with duplicated chromosomes

•separates the members of each homologous pair and produces two daughter cells, each with one set of chromosomes.

* starts with the pairing of homologous chromosomes 

Meiosis II

the sister chromatids separate and create four haploid cells

Know the different between Mitosis and Meiosis

–Mitosis produces __two genetically identical__ diploid somatic daughter cells.

–Meiosis produces __four genetically unique__ haploid gametes.

* How are they similar
* Both mitosis and meiosis begin with diploid parent cells that have chromosomes duplicated during the previous interphase.

Crossing Over

an exchange of corresponding segments between nonsister chromatids of homologous chromosomes

What is a Karyotype

it is a Photographic inventory of an individual chromosomes

How do you prepare them?

•white blood cells are isolated, stimulated to grow, arrested at metaphase stained to reveal band patterns, and

photographed under a microscope

The chromosomes are arranged into ordered pairs so that any chromosomal abnormalities can be detected

What is nondisjunction?

•An abnormal chromosome count is the result of **nondisjunction**, which can result when members of a chromosome pair fail to separate during meiosis:

–the failure of a pair of homologous chromosomes to separate during meiosis I or

–the failure of sister chromatids to separate during meiosis I IWhic

Which chromosomal abnormality causes Down Syndrome?

Trisomy 21 results in Down syndrome

The copies fo chromosome 21 fail to separate during meiosis

What are the sex chromosomes of individuals with Turner Syndrome and Klinefelter Syndrome? 

Klinefelter Syndrome (male)- XXY

Turner Syndrome (female)- XO

Describe the 4 types of changes in chromosome structure due to chromosome breakage

Chromosome breakage can lead to rearrangements—**deletions**, **duplications**, **inversions**, and **translocations**—that can produce genetic disorders or, if the changes occur in somatic cells, cancer

Who was Mendel? What organism did Mendel study? 

He was the guy who studied the pea plant

Heredity

•is the transmission of traits from one generation to the next.

–You inherit traits from your parents

Genetics

* **(**the __scientific study of heredity__) began with Gregor Mendel’s experiments.

–A heritable feature that varies among individuals is called a character.

–Mendel crossed pea plants and traced **traits**(variants of a character) from generation to generation.

Distinguish between true-breeding, hybrids, the P generation, F1 generation, and F2 generation

True-Breeding-

Hybrids- offspring of two different varieties

P generation- parent generation

F1 generation-first generation of offspring

F2 generation- offspring of F1 generation

Alleles

alternative versions of gene that account for variations in inherited characters

Homozygous

An organism that has two identical alleles for a gene

Heterozygous

an organism that had two different alleles for a gene

Dominant Allele

if the two alleles of an inherited pair differ (heterozygous) and one determines the organism’s appearance

Recessive Allele

one of the alleles has no noticeable effect on the organism’s appearance

Law of Segregation

A sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes (meiosis).G

Genotype

the different variations in the punnet square

Ex: PP, Pp, Yg

Examples- BB; homozygous dominant

Bb; Heterozygous

bb; homozygous recessive

Phenotype

what it looks like

Ratio example- 3 purple : 1 white

Monohybrid Cross

a cross between two individuals that are heterozygous for one character

Dihybrid Cross

a cross between two organisms that are each heterozygous for two characters being followed

Mendel’s Law of Independent Assortment

the alleles of a pair segregate independently of other allele pairs during gamete formation

What is the purpose of a test cross

it can reveal the unknown genotype, a mating between an individual of unknown genotype and a homozygous recessive individual, 

Pedigrees

a family tree of traits of parents and children across generations

we use this to deduce the genetic information, and can also determine individual genotypes

The ABO Blood Group

this phenotype in humans is controlled by three alleles that produce a total of four phenotypes

Codominant

•Both alleles are expressed in heterozygous individuals *(IAIB)*, who have type A B blood

Pleiotropy

occurs when one gene influences multiple characters

Sickle-cell Disease

*  is a human example of pleiotropy.

–This disease affects the type of hemoglobin produced and the shape of red blood cells, andcauses anemia and organ damage.

–Sickle-cell and nonsickle alleles are codominant.

–Carriers of sickle-cell disease have increased resistance to malaria.

Polygenic Inheritance

which a single phenotypic character results from the additive effects of two or more genes on a single phenotypic character

* ex; human height

Linked Genes

–are located close together on the same chromosome and

–tend to be inherited together.

–These genes __do not follow__ the Law of independent assortment

Crossing Over

homologous chromosomes produces new combinations of alleles in gametes

•Linked genes can be separated by crossing over, forming recombinant gametes.

•The percentage of recombinant offspring among the total is the recombination frequency.

Sex Chromosomes

Males- XY

Female- XX

–The Y chromosome has genes for the development of testes, whereas an absence of the Y allows ovaries to develop.

•In humans, however, if this gene is not turned on, ovaries develop even in an XY embryo

•In humans, sex is determined by the interactions of several proteins produced by different genes, including autosomal (non-sex chromosome) genes.

–Because of this complexity we now know that sex in humans is not a binary state, and has many variations

Sex-linkes gene

a gene located on either sex chromosome

X-linked Gene

control trains unrelated to sex

–Red-green colorblindness

–Hemophilia – lack protein required for blood clotting

Recessive Disorders

Must be homozygous for the allele

Albinism, Cystic Fibrosis, Phenylketonuria (P K U), Sickle-cell disease, Tay-Sachs disease

Dominant Disorders

can be heterozygous because it is dominant

Achondroplasia, Huntington’s disease, Hypercholesterolemia

Experiments leading up to and including the description of DNA with the following scientist(s): Watson and Crick, Rosalind Franklin, Hershey and Chase, Chargaff 

Watson and Crick-were the first to the finish line (their paper showing the model of DNA was published in 1953), their model gave new meaning to the words *genes* and *chromosomes.* The genetic information in a chromosome is encoded in the nucleotide sequence of D N A.

Rosalind Franklin- had taken an x-ray image of DNA and knew that the sugar-phosphate backbone was on the outside and the nitrogenous bases were on the inside

Hershey and Chase- able to show that certain **bacteriophages** (or **phages,** bacterial viruses) reprogram host cells to produce more phages by injecting their DNA

Chargaff-was a biochemist and had discovered that the amount of C in DNA equaled the amount of G 

What is the monomer of nucleic acids DNA and RNA? What are the 3 components of the monomer? What are the nitrogenous bases? 

•D N A and R N A are nucleic acids consisting of long chains (polymers) of chemical units (monomers) called **nucleotides**.

* One of the two strands of D N A is a D N A **polynucleotide**, a nucleotide polymer (chain)

•A nucleotide is composed of a nitrogenous base, five-carbon sugar, and phosphate group.

•Each type of D N A nucleotide has a different nitrogen-containing base: **adenine** (A), **cytosine** (C), **thymine**(T), and **guanine** (G)

The nucleotides are joined to one another by 

a sugar-phosphate backbone

Nitrogenous bases of DNA 

Functional groups determine which two bases can form hydrogen bonds

The full name for **DNA** is **deoxyribonucleic acid**, with *nucleic* referring to what?

DNA’s location in the nuclei of eukaryotic cells

RNA (ribonucleic acid)

–Is single stranded

–uses the sugar ribose (instead of deoxyribose in D N A) and

has a nitrogenous base **uracil** (U) instead of thymine

DNA replication

•starts with the separation of D N A strands.

•Enzymes then use each strand as a template to assemble new nucleotides into a complementary strand.

•requires the coordination of more than a dozen enzymes and other proteins

•DNA is untwisted and the two new strands are made roughly simultaneously

•Human cells have more than 6 billion base pairs but can replicate in a few hours

•Accurate - only about one nucleotide in several billion is mispaired

Semiconservative model

–The two D N A strands separate.

–Each strand then becomes a template for the assembly of a complementary strand from a supply of free nucleotides.

–__Each new D N A helix has one old strand with one new strand (half of the parent molecule is conserved in each ‘daughter’ molecule).__

DNA polymerase

the cell synthesizes one daughter strand as a continuous piece

DNA Ligase

The other strand is synthesized as a series of short pieces, which are then connected by this enzyme 

Transcription

(Nucleus)

•is the synthesis of R N A under the direction of DNA

Translation

(cytoplasm)

is the synthesis of proteins under the direction of RNA

What is a gene?

•is defined as a region of DNA that can be expressed to produce a functional product that is either a polypeptide or an R N A molecule.

–Recall that a polypeptide is a polymer of a protein

Triplet Code

The genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of non overlapping three-base “words” called **codons**.

Be able to translate DNA to RNA

AAACCGGCAAAA

UUUGGCCGUUUU

The genetic code

•is instructions contained in a gene that tell a cell how to make a specific protein

–The amino acid __translation__ of the nucleotide triplets

•Nearly all organisms use an identical genetic code to convert the m R N A codons transcribed from a gene to the amino acid sequence of a polypeptide.

RNA polymerase 

•joins them along one strand of the D N A, following the base-pairing rules.

–A specific nucleotide sequence called a promoter acts as a binding site for R N A polymerase and determines where transcription starts.

In the nucleus, the D N A helix unzips, and R N A nucleotides line up 

Messenger RNA (mRNA)

conveys genetic messages from D N A to the translation machinery of the cell (ribosomes).

Before leaving the nucleus as m R N A, eukaryotic transcripts undergo __two__ modifications:

the product of **transcription**, carries genetic information from DNA to a ribosome

RNA splicing

**introns** (noncoding segments of R N A) are spliced out “intragenic region”,

**exons** (the parts of a gene that are expressed) are spliced together

Multiple polypeptides from a single gene

Cap and Tail

are added to the ends of the m R N A

§Facilitate export out of the nucleus, protect the mRNA from degradation, and help the ribosome bind to the mRNA.

Transfer RNA (tRNA)

A ribosome attaches to the m R N A and translates its message into a specific polypeptide,

tRNAs transfer amino acids from the ‘cytoplasmic pool’ and add them to the growing polypeptide

–Each t R N A is a folded molecule bearing a base triplet called an **anticodon** on one end and a specific amino acid attachment site at the other end.

needed for **translation**. Carries a specific amino acid (coded by mRNA) to the ribosome

Ribosomes

are structures in the cytoplasm that coordinate functioning of m R N A and t R N A and catalyze the synthesis of polypeptides

Ribosomal RNA (rRNA)

Ribosomes are made of rRNA and proteins and have binding sites for tRNA and mRNA

RNA that (combined with proteins) makes up ribosomes, which **translate** mRNA into proteins 

Translation brings together

–mRNA,

–a tRNA bearing the first amino acid, and

–the two subunits of a ribosome.

The flow of genetic information

•DNA transcribed to RNA in the nucleus

•RNA is processed (mRNA) and exits the nucleus (in eukaryotes)

•mRNA and tRNA with a specific amino acid are used by the ribosome to create a polypeptide

•Polypeptide folds into 3-dimensional tertiary structure which determine its function 

Mutations

•are changes in the genetic information of a cell or virus, caused by errors in D N A replication or recombination, or by physical or chemical agents called **mutagens**.

–Examples of mutagens: high energy radiation such as X-rays or UV light, tobacco products, radioactive substances

•Substituting, inserting, or deleting nucleotides alters a gene, with varying effects.

Elongations

Elongation continues until a **stop codon** reaches the ribosome’s A site