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What is the basic units of life in all living organisms.
Life on earth can be traced back 3.7 billion years to single celled organisms, such as bacteria and blue-green algae.
Eukaryotic cells, cells with a nucleus, appeared 1.2 billion years ago.
A three-dimensional structure composed of carbohydrates, lipids (fats), nucleic acids, and proteins
A discrete unit surrounded by a thin membrane, called the nuclear membrane.
Inside are two kinds of nucleic acids, molecules that contain genetic information that controls the cell’s function.
Structures made up of two or more atoms.
Molecules can combine with other molecules to form more complex structures.
¨DNA (deoxyribonucleic acid)
¨RNA (ribonucleic acid)
- ¨Surrounds he nucleus and contains many other types of organelles involved in various activities, such as breaking down nutrients and converting them to other substances, storing and releasing energy, releasing waste, and
- manufacturing proteins in a process called protein synthesis.
Mitochondria - oval structures enclosed within a folded membrane, containing their own distinct DNA, called mitochondrial DNA (mtDNA)
Ribosomes – roughly symmetrical and partly composed of RNA; essential in protein synthesis
- cellular components of body tissues, such as
- muscle, bone, skin, nerve, heart, and brain
sex cells involved in reproduction and not important as structural components of the body
Egg cells produced in female ovaries
Sperm cells produced in male testes
union of sex cells to form the potential of developing into a new individual; in this way gametes transmit genetic information from parent to offspring.
Cellular function and an organism’sinheritance depends on the
structure and function of DNA
DNA is composed of
two chains of nucleotides, comprising a double strand or double helix.
A nucleotide consists of
a sugar, a phosphate, and one of four nitrogenous bases.
DNA Structure, two chains are held together by
bonds formed on their bases with their complement on the other chain.
- ¤Adenine (A) is the complement
- of Thymine(T)
- ¤Guanine(G) is the complement
- of Cytosine(C)
Cells multiply by dividing, making exact copies of themselves and enabling organisms to grow and injured tissues to heal.
The DNA molecule is able to make copies of itself.
Specialized proteins that initiate and direct chemical reactions in the body.
- Replication begins when enzymes break the bonds between bases throughout the DNA molecule, separating two previously joined strands of nucleotides and leaving their bases
The DNA Replication Process
Enzymes break the bonds between the DNA molecule.
- Two nucleotide chains serve as templates for the formation of a new strand of
Unattached nucleotides pair with the appropriate complementary nucleotide.
Complex, three dimensional molecules that function through their ability to bind to other molecules
The protein hemoglobin, found in red blood cells, is able to bind to oxygen, which carries it throughout the body
Ribosomes help convert the genetic message from the DNA into proteins.
Messenger RNA (mRNA) carries the genetic message from the cell nucleus to the ribosome.
- ¨Transfer RNA (tRNA), found in the cytoplasm, binds to one specific amino
Small molecules that are the components of proteins.
Amino acids are the building blocks of protein.
- Proteins differ according to number of amino acids and the sequence in which they are
Hemoglobin molecules are composed of four chains of amino acids (two “alpha” chains and two “beta” chains).
The red structures are the portions that bind to oxygen
Substances (usually proteins) that are produced by specialized cells and travel to other parts of the body, where they influence chemical reactions and regulate various cellular functions.
RNA and DNA
RNA differs from DNA in three important ways:
1.It’s usually single-stranded. (This is true of the forms we discuss, but it’s not true for all.)
- contains a different type of sugar.
3.It contains the base uracil as a substitute for the DNA base thymine. (Uracil is attracted to adenine, just as thymine is.)
Messenger RNA (mRNA)
A form of RNA that’s assembled on a sequence of DNA bases.
It carries the DNA code to the ribosome during protein synthesis
¨Triplets of messenger RNA bases that code for specific amino acids during protein synthesis.
Transfer RNA (tRNA)
¨The type of RNA that binds to amino acids and transports them to the ribosome during protein synthesis.
Protein Synthesis: Transcription
The process of coding a genetic message for proteins by formation of mRNA.
A portion of the DNA unwinds and serves as a template for the formation of a mRNA strand.
The two DNA strands have partly separated.
Free messenger RNA (mRNA) nucleotides have been drawn to the template strand, and a strand of mRNA is being made.
Note that the mRNA strand will exactly complement the DNA template strand, except that uracil (U) replaces thymine (T).
Protein Synthesis: Translation
The mRNA travels through the nuclear membrane to the ribosome.
tRNAs arrive at the ribosome carrying their specific amino acids.
The base triplets on the tRNA match up with the codons on the mRNA.
As each tRNA line up in the sequence of mRNA codons their amino acids link to form a protein.
What is a Gene?
A gene is the entire sequence of DNA bases responsible for the synthesis of a protein.
A mutation occurs when the sequence of bases in a gene is altered.
- Mutations may interfere with the ability to produce vital protein and may lead to a new
- variety within the species, hence, evolution.
Noncoding sequences are called
introns, and are initially transcribed into mRNA and then clipped out
Recently, geneticists have learned that only some parts of genes are actually transcribed into mRNA (most of the nucleotide sequences in genes are not expressed during protein synthesis).
What is this part called
- Genes that code for the production of proteins that can bind to DNA and modify the
- action of genes.
Many are active only during certain stages of development.
Homeobox Genes (Hox genes)
An evolutionarily ancient family of regulatory genes (highly conserved) that directs the development of the overall body plan and the segmentation of body tissues.
Function of Hox Genes
determine the overall pattern of each type of vertebra and of each individual vertebra
¨Cell division results in production of new cells.
¨During cell division:
¤Cells are involved with normal cellular and metabolic processes.
¤The cell’s DNA becomes tightly coiled.
¤DNA is visible under a microscope as chromosomes.
During normal cell functions, chromosomes exist as
A chromosome is composed of a
DNA molecule and associated proteins.
During cell division, chromosomes consist of
two strands of DNA joined at the centromere.
Humans have how many chromosomes
Chromosome pairs are called
¤They carry genetic information that influences the same traits.
¤They are not genetically identical.
Number of Chromosome in Chipanzee and Gorillas
Types of Chromosomes
Autosomes - govern all physical characteristics except sex determination
¨Sex chromosomes - X and Y chromosome.
¤Mammal females have two X chromosomes.
¤Mammal males have one X and one Y chromosome.
Mitosis is cell division in somatic cells.
- Mitosis occurs during growth and
- repair/replacement of tissues.
The result of mitosis is two identical daughter cells that are genetically identical to the original cell.
Steps in Mitosis
1.The 46 chromosomes line up in the center of the cell.
2.The chromosomes are pulled apart at the centromere.
3.The strands separate and move to opposite ends of the dividing cell.
4.The cell membrane pinches in and two new cells exist.
Cell division in specialized cells in ovaries and testes.
- Meiosis involves two divisions and results in four daughter cells, each containing only
- half the original number of chromosomes.
These cells can develop into gametes.
Sometimes called crossing over; the exchange of genetic material between partner chromosomes during meiosis.
Evolutionary Significance of Meiosis
Meiosis and sexual reproduction are highly important evolutionary innovations.
Meiosis increases genetic variation at a faster rate than mutation.
Offspring in sexually reproducing species represent the combination of genetic information from two parents.
Problems with Meiosis
In order for fetal development to occur normally, the meiotic process needs to be exact
If chromosomes or chromosome strands do not separate during either of the two divisions, serious problems can develop
Failure to separate is called nondisjunction
Polymerase Chain Reaction (PCR)
Allows scientists to make of copies of DNA samples which can then be analyzed.
Scientists use PCR to:
- ¤Examine nucleotide
- sequences in Neandertal fossils and Egyptian mummies
- ¤Identify an
- individual DNA sequences.
¤Identify remains of victims of 911.
¤Exonerate people wrongly convicted of crimes.
Recombinant DNA Technology
- A process in which genes from the cell of one species are transferred to somatic cells or
- gametes of another species.
Production of human gene products such as insulin
Organisms that are genetically identical to another organism.
- The term may also be used in referring to genetically identical DNA segments, molecules,
- and cells.
Human Genome Project
- Effort begun in 1990 to sequence the entire human genome, which consists of some 3
- billion bases comprising approximately 25,000 to 30,000 genes.
The goal was achieved in 2003.
- Scientists are still several years away from identifying the functions of many of the
- proteins produced by these genes.