Anthropology Mini Essays

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Lecture 4: Cell Biology and Protein Synthesis

Key Questions

• What are the types of cells that make up human bodies?

• What is the most important function of a gene (of DNA)?

• What are the steps of protein synthesis?

• What are the two types of cell division?

• What is the evolutionary significance of meiosis?

The Cell

Eukaryotic Cells

• Structurally complex cells composed of carbohydrates, lipids (fats), nucleic acids, proteins. – First appeared 1.2 billion years ago

• Somatic cells—cells of the body and body tissues; skeletal cells, muscle cells, neurons, blood cells; all cells in the body are somatic cells except for the gametes

• Gametes—sex cells; sperm are the male sex cell and are produced in the testes; ova are the fema

Chromosomes

https://www.mun.ca/biology/scarr/Karyotype_Denver_system.jpg

Chromosomes • Humans have 46 (23

homologous pairs)

• Diploid chromosomes—the full complement of chromosomes in a somatic cell

• Haploid chromosomes— half the complement of chromosomes, one member of each pairsex cells

Structures composed of a DNA molecule and associated proteins

Chromosomes

• Autosomes— chromosomes that carry the genetic information for all physical characteristics EXCEPT sex (44 of the 46 chromosomes in humans)

Structures composed of a DNA molecule and associated proteins

Chromosomes

• Autosomes— chromosomes that carry the genetic information for all physical characteristics EXCEPT sex (44 of the 46 chromosomes in humans)

• Sex chromosomes

– X and Y

– XX for female

– XY for male

Structures composed of a DNA molecule and associated proteins

DNA and Chromosomes

1 trillion somatic cells

46 chromosomes per cell

100-1000 genes per chromosome

DNA is coiled

around specialized

proteins that give it structure

a specific sequence of nucleotide base pairs make a gene

1 trillion somatic cells

46 chromosomes per cell

100-1000 genes per chromosome

DNA is coiled

around specialized

proteins that give it structure

a specific sequence of nucleotide base pairs make a gene

DNA Structure

Proteins

http://trc.ucdavis.edu/biosci10v/bis10v/week2/2webimages/0143.gif http://www.irondisorders.org/News/SickleCell.jpg

Proteins

• The primary function of DNA is protein synthesis

• Proteins:

– Chains of amino acids

– Built from DNA/genes

– Amino acid order is determined by gene

– Amino acid order is crucial to protein function

http://image.slidesharecdn.com/proteinsandaminoacids-140714080054- phpapp02/95/proteins-and-amino-acids-32-638.jpg?cb=1405326023

Protein Synthesis

http://anthro.palomar.edu/biobasis/bio_5.htm

RiboNucleic Acid

• Similar to DNA structure

• Various types/functions

• Single stranded

• Uracil replaces thymine

• Facilitates protein synthesis

– turns genes into functions

http://tigger.uic.edu/classes/phys/phys461/phys450/ANJUM04/RNA_sstrand.jpg

Transcription

• Messenger RNA (mRNA) • Copies order of bases • Takes code out of nucleus

Translation Transfer RNA (tRNA)

“Reads” mRNA’s message

Strings amino acids together

Constructs proteins

Protein Synthesis

• https://youtu.be/I_c8GlWRQJo

Sickle-Cell Anemia

https://www.fi.edu/sites/default/files/styles/featured_large/public/General_EduRes_Heart_RedBloodCel ls.jpg?itok=mTMuH5xK

Sickle-Cell Anemia

• Disease that affects shape of hemoglobin—molecule that carries oxygen in blood – Abnormal hemoglobin can clog blood vessels—causes

major life-threatening problems

• Hemoglobin is a protein, which is produced by protein synthesis based on the information in a gene – Abnormal cells result from a mutation in the DNA

sequence that codes for hemoglobin—a different allele, or version of the hemoglobin gene

– Mutation—minor alteration in the sequence of bases in a DNA strand

• This tiny alteration makes major changes in the protein that interrupt its normal function and cause disease

Sickle Cell Anemia

From: Campbell NA, Reece JB. 2002. Biology, 6th Ed. San Francisco: Benjamin Cummings. SCA mutant hemoglobin results from change in ONE amino acid (out of 146 in the whole hemoglobin chain)

Sickle-Cell Anemia

• There are 146 amino acids in the chain for hemoglobin.

– Sickling hemoglobin is caused by a change in just one nucleotide base in the gene for hemoglobin, leading to a change in just one amino acid.

Sickle-Cell Anemia

Cell Division

J. BRILL et al., Curr. Biol. 15, 1401–1406 and 1407–1412 (2005)

Cell Division

• Mitosis—cell division in somatic cells; cells make identical copies of themselves

– Start with 1 diploid cell, end with 2 identical diploid cells

• Meiosis—cell division in gametes

– Start with 1 diploid cell, end with 4 distinct haploid cells

DNA Replication

Mitosis

1 2

6 5 4

3

1. DNA replicates (4 copies of each chromosome, 2 pair homologous chromosomes

2. Nuclear membrane disappears

3. Chromosomes align at center of cell

4. Separate into pairs 5. Move to opposite sides of

cell (2 copies of each chromosome to each side)

6. Cell membrane pinches, creates 2 new diploid cells

Meiosis

Essentially the same as mitosis EXCEPT Recombination occurs

Meiosis

Exchange of genetic material between homologous chromosomes. Mixes it up even more than sexual reproduction would alone—some genes from the maternal and paternal chromosomes trade places.

Meiosis

An extra division of chromosome pairs produces FOUR HAPLOID daughter cells

Mitosis vs. Meiosis

Errors in Meiosis

Significance of Meiosis

• For Evolution:

– Increases variation

• Variation is one of the Necessary and Sufficient Conditions for Natural Selection

• Raw material on which selection acts

• Errors:

– Copying errors = wrong proteins produced

– Nondisjuction = trisomy (21, sex chromosomes)

– Sometimes, errors turn out to be beneficial