Chapter 3: Biological basis of life: genetics, cells, DNA

1

Constraints on Darwin's theory of natural selection

Constraint 1: Didn't know there's biological variation in all species.

Constraint 2: Didn't know how traits were inherited.

2

Cells: the basic units of life

3.5 bya (billion years ago) primitive cellular forms emerged-similar to modern day algae

1.7 bya earliest modern, eukaryotic cells emerged

3

Cells: the basic units of life

4

*Somatic cells

*Sex cells

DNA-chains of stacked nucleotides

-nucleotide structure

Sides: a sugar and a phosphate

Rungs: bases pairs

Adenine

Thymine

Guanine

Cytosine

Bases form complementary bonds5

DNA compared to RNA

RNA-single-stranded-Uracil base instead of thymine

6

Proteins-complex molecules able to bind with other molecules-composed of amino acid chains

Amino acids -basic building blocks of proteins-sequence and number determine protein function

Triplets: sequence of 3 DNA bases specifies amino acids

7

8

DNA replication

1. DNA unzips

2. Exposed bases attract

complementary nucleotides

3. Two original strands are

templates for new strands

9

DNA function: protein synthesis

Part 1 (transcription) in the nucleus...-mRNA copies DNA bases three at a time (triplets) into codons

Part 2 (translation) in the cytoplasm with ribosomes...-tRNA binds amino acids with complementary codons

10

Proteins

Structural: form an organism's physical attributes (keratin, collagen)

Functional: regulate chemical activities (enzymes, hormones)

11

Proteins examples

E.g., Hormones -produced by specialized cells -influence chemical reactions -regulates various cell functions

E.g., Hemoglobin is a protein molecule found on red blood cells. Hb binds with oxygen and carries it throughout the body.

12

Humans have 46 Chromosomes-coiled DNA visible during cell replication-each human somatic cell has 46 (23 pairs)

Autosomes -carry genetic information that governs all physical characteristics

Sex chromosomes-determines primary sex

X chromosome = femaleY chromosome = male

13

14

Human Genome Project-complete sequence of DNA bases that specifies the order of amino acids in an entire protein, part of protein, or any functional product

Human Genome-25,000 genes-90,000 proteins

15

Genes

16

Mitosis: somatic cell division

17

-occurs during growth, repair, and replacement of tissues

Result: 2 genetically identical daughter cells-46 chromosomes

Meiosis: sex cell division

18

Two cell divisions 1st division: reduction2d division: similar to mitosis

Result: 4 genetically different daughter cells -23 chromosomes

Recombination

-paired chromosomes exchange genes during meiosis

-new combination of genetic material is inherited

19

Recombination

-exchange of genetic material between paired chromosomes at the beginning of meiosis.

-New combinations of existing genes arise at the beginning of meiosis when homologous pairs of chromosomes from each parent exchange genetic material.

-new combination of genetic material is inherited20