Module 2: Continuity and Unity of Life (Biology Keystones)

The Cell Cycle

Sequence of events in the life of a dividing EUKARYOTIC cell. Cells leave Gap 1 when they need to divide for cell repair, growth of the organism, or asexual reproduction.

Binary fission

PROKARYOTIC cell division

____________________________ is the longest phase of the cell cycle - includes G1, S, G2

Interphase

______________________________ is nuclear and cell division - only time you can see chromosomes

Mitotic phase

______________ is uncontrolled cell growth & division - the affected cells do not stop dividing and form tumors; could spread throughout the body = __________________

Caner, metastize

Mitosis

Nuclear division of body cells

Function: Cell growth, replace damaged cells

Reproduction: Asexual reproduction

Cells: Somatic (body) cells

Genetically: Identical

Crossing over: No

Homologous pairs: No

of divisions: 1

of daughter cells: 2 (diploid)

Chromosome #: Same

Meiosis

Reduction division of the nucleus in sex cells

Function: Produce gametes, reduce the chromosome number (halved)

Reproduction: Sexual reproduction

Cells: Sex cells (gametes)

Genetically: Different

Crossing Over: Yes

Homologous pairs: Yes

of divisions: 2

of daughter cells: 4 (haploid)

Chromosome #: Half

Source of Variation during Meiosis

Meiosis provides the opportunity for shuffling of chromosomes and genetic recombination, increasing biodiversity. It's a good thing!

Crossing over

Occurs when two homologous chromosomes overlap and exchange genes

Nondisjunction

"not coming apart" - failure of chromosomes to separate during Anaphase 1 or 2

Deletion

Part of a chromosome or sequence of DNA is missing

Duplication

Two or more copies of a gene or of a segment of a chromosome

Translocation

Transfer of part of a chromosome to another location (non-homologous chromosomes)

Inversion

Reversal of genes on a chromosome

Insertion

Addition of one or more nucleotides into a DNA sequence

Point Mutation (base substitution)

One nucleotide is replaced (substituted) by another

Nonsense mutation

Results in a stop codon being inserted before the end of the gene = shorter protein

Missense mutation

Results in the wrong amino acid

Frameshift mutation

Insertion or deletion that shifts the reading frame

Genetics

Study of heredity - transmission of genetic characteristics from one generation to the next

Allele

B or b (different forms of a gene)

Genotype

Genetic make up or an organism (Bb)

Phenotype

Physical appearance of the organism (brown)

Homozygous dominant

BB

Heterozygous

Bb

Homozygous recessive

bb

Incomplete dominance

Heterozygotes show a blended phenotype

BB = black

BW = gray

WW = white

Codominance

Both alleles are expressed in the heterozygotes

BB or IBIB = black

BW or IBIW = gray

WW or IWIW = white

Sex-linked traits

Genes located on the X-chromosome, more common in males

Polygenic traits

Many genes contribute to an overall phenotype - shows up like a bell curve

Multiple alleles

More than 2 alleles for one trait, like blood type

A = AA, AO or IAIA or IAi

B = BB, BO, or IBIB, or IBi

AB = AB or IAIB

O = OO or ii

Important features of DNA

• Monomer: nucleotides = phosphate + deoxyribose + one of 4 nitrogenous bases (A, T, C, G)

• A pairs with T, C pairs with G

• Double helix shape

• DNA strands or complementary (not identical)

• DNA is antiparallel (opposite orientation -> one strand is 3'-5' the other runs 5'-3')

• Replication is semi-conservative = each DNA molecule has one original and one new strand

• In the form of chromatin during interphase, chromosomes/chromatids during cell division

DNA replication

Only when a cell needs to divide

How does it work??

The double helix unwinds (using helicase) and separates into two template strands. DNA polymerase adds new nucleotides complementary to the template strand.

There are hundreds of replication forks in eukaryotes, only one in prokaryotes (goes in 2 directions)

DNA

• Double stranded

• A, T, C, G

• Sugar = deoxyribose

• Stays in nucleus

RNA

• Single stranded

• A, U, C, G

• Sugar = ribose

• Can leave the nucleus

Protein Synthesis (The central Dogma)

In order for genes to be expressed (have the traits show up), they must be transcribed and translated into proteins.

Transcription (DNA -> RNA)

DNA is transcribed into mRNA (messenger) by RNA polymerase, mRNA carries the genetic info out of the nucleus.

Translation (RNA -> Protein)

Translation occurs in the cytoplasm at the ribosome. It is the process of converting the genetic info carried by mRNA into an amino acid sequence. tRNA transfers amino acids to the ribose that correspond to the mRNA's codons (3 nucleotides in mRNA). The protein is assembled.

Steps of Translation

1. The mRNA is read in triplet code: 3 nucleotides = 1 codon.

2. Each codon codes for a specific amino acid. Use this chart (or the table below) to determine which amino acid is coded for, using the mRNA codons (Big letters inside to make small letters outside).

3. Complementary tRNA carriers the corresponding amino acid to the ribosome. tRNA has 3 anticodons that are complementary to the mRNA.

4. Ribosome bonds amino acids together with a peptide bond. The amino acid sequence becomes the polypeptide (which will fold up to the functioning protein). The sequence ends at a stop codon.

Selective breeding

People choose only organisms with desirable traits to reproduce, making the alleles for these traits more common (also called artificial selection)

Hybrid

Cross between two breeds or two closely related species

Genetic engineering

Involves directly inserting, removing, or altering an organisms DNA

Genetically Modified Organism (GMO)

Contains DNA from other organisms. GMO's are also called transgenic organisms because they contain transcends, or genes from other species.

Gene splicing

DNA is cut apart and recombined in different ways. Recombinant DNA, combined from several sources, is created in this way.

Restriction enzymes

Cut up DNA at specific restriction sites. The sites are the locations where DNA from different organisms can combine.

Enzymes are proteins that catalyze a reaction. Enzymes are used to cut DNA at specific sites and bring pieces of DNA together

Genetic engineering is used to produce proteins like insulin. The gene from human insulin is cut and spliced into a plasmid (small, circular, DNA in bacteria). The bacteria make the hormone using that DNA

Gene Therapy

Changes the DNA of a person with a genetic disease (nonfunctioning gene) by introducing working genes into cell nuclei - disorders caused by a single gene are the best targets for gene therapy.

Forensics: Use of science and technology to investigate and solve crimes

Short Tandem Repeats (STR)

Nongenetic DNA sequences that differ among individuals, making them useful in identification

CODIS

FBI database that stores DNA fingerprints. CODIS stores information on alleles at 13 different STR loci for each person on file

Polymerase Chain Reaction (PCR)

Technique that makes multiple copies of even minuscule amounts of DNA - allows them to be visualized on an agarose gel

Gel electrophoresis

Separates DNA by size (restriction enzymes cut fragments of DNA around their STR's to make different size fragments) - an electric current causes the DNA fragments to move toward the other end, small fragments move faster than large.

Examining STR's at several different loci allows investigators to distinguish DNA from different individuals.