Copyright © 2013 Pearson Education, Inc. All rights reserved. Chapter 3 Genetics: Cells and Molecules

Copyright © 2013 Pearson Education, Inc. All rights reserved.

Chapter 3Genetics: Cells and Molecules


Genetics

• The Study of Genetics–Cellular and molecular genetics–Classical and Mendelian genetics–Population genetics–Phylogenetics–Behavioral genetics


The Cell

• The basic building block of life

• Single celled organisms

• Multicellular organisms

• Prokaryotes– No compartments for

genetic material

• Eukaryotes– Separated genetic

material


Cell Anatomy (Eukaryotic)

• Nucleus– Deoxyribonucleic Acid (DNA)

• Gametes • Cytoplasm• Cell Membrane• Mitochondria• Ribosomes• Endoplasmic Reticulum


DNA Structure I: The Molecular Level

• DNA Structure I: The Molecular Level– Double Helix– Nucleotide• Sugar• Phosphate• Base

– Purines» Adenine» Guanine

– Pyrimidines» Cytosine» Thymine


DNA Function I: Replication

Separate Strands Enzymes

MutationsProofreading and

Repair

The DNA Molecule

James Watson (left) and Francis Crick in 1953 with their model of the structure of the DNA molecule.

Part of a DNA Molecule

DNA Replication

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 nucleotides.

Unattached nucleotides pair with the appropriate complementary nucleotide.

Protein Synthesis

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 acid.

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.)

2. It 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.

Codons

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.

Transcription

Transcription

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.


DNA Function II: Protein Synthesis

• Proteins– Compose bone and

muscle– Hormones– Enzymes– Cellular function

• Protein Synthesis– Amino acids– Dipeptides– Polypeptide chains


DNA Function II: Protein Synthesis (cont’d)

• Genetic Code– Nucleotides– Codons– Genes

• Redundancy

• Transcription and Translation– mRNA– tRNA– Introns– Exons

Cell Division

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.

Chromosomes

Scanning electron micrograph of human chromosomes during cell division.

Note that these chromosomes are composed of two strands, or two DNA molecules.

Chromosome Structure

A chromosome is composed of a DNA molecule and associated proteins.

During normal cell functions, chromosomes exist as single-stranded structures.

During cell division, chromosomes consist of two strands of DNA joined at the centromere.

Since the DNA molecules have replicated, one strand of a chromosome is an exact copy of the other.

Chromosomes and Genetics

Each species is characterized by a specific number of chromosomes. Humans have 46 chromosomes.

Chromosome pairs are called homologus: They carry genetic information that

influences the same traits. They are not genetically identical.

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

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.

Mitosis

The cell is involved in metabolic activities.

DNA replication occurs, but chromosomes are not visible.

Mitosis

The nuclear membrane disappears, and double-stranded chromosomes are visible.

Mitosis

The chromosomes align themselves at the center of the cell.

Mitosis

The chromosomes split at the centromere, and the strands separate and move to opposite ends of the dividing cell.

Mitosis

The cell membrane pinches in as the cell continues to divide.

The chromosomes begin to uncoil (not shown here).

Mitosis

After mitosis is complete, there are two identical daughter cells.

The nuclear membrane is present, and chromosomes are no longer visible.

Meiosis

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.

Recombination

Sometimes called crossing over; the exchange of genetic material between partner chromosomes during meiosis.

Mitosis

Meiosis

• Similar to the formal already present for the presentation of Mitosis

• Meiosis is ultimately more important to understand, so it is even more deserving of a detailed presentation

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


DNA Structure II: Chromosomes and Cell Division

• Chromatin State• Chromosomes form– Centromere– Diploid somatic cells– Haploid sex cells

• Mitosis– Somatic cell division

• Meiosis– Sex cell division


DNA Structure II: Chromosomes and Cell Division (cont’d)

• Mitosis– Interphase– Prophase– Metaphase– Anaphase– Telophase

• Meiosis– Tetrad formation– Crossing over– Recombination– Reduction division– Second Meiotic Division


Chromosomal Abnormalities

• Nondisjunctive Errors: The failure of homologous chromosomes to separate properly during cell division–Monosomy• Turner Syndrome

– Trisomy• Down’s Syndrome


Molecular Tools for Bioanthropological Research

• Indirect Methods– Immunological Methods– DNA Hybridization

• Direct Methods– DNA Sequencing– Protein Sequencing


Molecular Tools for Bioanthropological Research (cont’d)

• PCR

• Mitochondrial DNA (mtDNA)

• Ancient DNA


Molecular Tools for Bioanthropological Research (cont’d)

• Polymerase Chain Reaction– The polymerase chain reaction (PCR) is a method

for the amplification of minute quantities of DNA– PCR makes possible the recovery of ancient DNA

from bone or fossil material, up to about 100,000 years old, provided that preservation conditions were adequate

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Copyright © 2013 Pearson Education, Inc. All rights reserved. Chapter 3 Genetics: Cells and Molecules