Exam 1 Notes

What are DNA and RNA made of?

A pentose sugar, a phosphate, and a nitrogenous base.

What differentiates DNA and RNA?

Their pentose sugars; RNA has ribose, DNA has deoxyribose.

What is a nucleotide?

Base + deoxyribose + phosphate.

What are the purines?

Adenine and guanine.

What are the pyrimidines?

Cytosine, thymine, and uracil.

What are Chargaff’s rules for base composition?

A to T ratio = 1; G to C ratio = 1; A+G = T+C

The two strands of DNA face in what way towards each other?

Antiparallel; One goes 5’ → 3’, the other 3’ → 5’.

Where are the phosphodiester bonds in DNA?

Between 5’-PO and 3’-OH groups of nucleotides on each strand.

Where are the hydrogen bonds in DNA?

Between complementary bases of opposite strands.

How many H-bonds do A-T base pairs have?

Two

How many H-bonds do G-C base pairs have?

Three

ssDNA

Single-stranded DNA

dsDNA

Double-stranded DNA

bp

Base pair = 1 pair of H-bonded bases in dsDNA

Kb

kilobase pair = 1,000 bases

Mb

Megabase pair = 1,000 Kb

What are the secondary structures of ssDNA and RNA?

Intramolecular H-bonds

What is the structure of the double helix?

Sugar-phosphate backbone; base pairs in the middle

What makes a prokaryote different from a eukaryote?

Prokaryotes are small. They have no membrane-bound nucleus and they have one giant circle of DNA.

What is the tertiary structure of prokaryotic DNA?

Supercoiling: additional winding or twisting of the double-helix DNA.

What do topoisomerases do?

Add or remove rotations in DNA by breaking and rejoining DNA strands.

What is the tertiary structure of eukaryotic DNA?

Linear chromosomes.

What are linear chromosomes organized of?

Chromatin: DNA & proteins

How many genes does each chromosome contain?

100s to 1000s

Each chromosome is approximately…

½ DNA, ½ proteins

About ½ of the proteins in a chromosome are…

Positively-charged histone proteins

Sexual reproduction:

Mixing of genomes via meiosis and fusion of gametes

Most unicellular gametes are…

Equally sized.

Male gametes are…

Small and mobile.

Female gametes are…

Large and stationary.

Dioecious species:

Either male or female reproductive structures are present in each individual.

Monoecious species:

Both male and female reproductive structures are present in each individual.

Sex determination:

Mechanism by which sexual phenotype is established.

Sex chromosome:

Chromosome involved in determining sex.

Autosome:

Chromosome NOT involved with determining sex.

Chromosomal sex:

Presence of chromosomes characteristic of a certain sex, as determined at fertilization.

Phenotypic sex:

Internal and external morphology of each sex, resulting from differences in gene expression.

In the XY system, females are __ and males are __.

XX; XY

In the ZW system, females are __ and males are __.

ZW; ZZ

Which is the homogametic sex in the XY system?

Females; XX

Which is the heterogametic sex in the XY system?

Males; XY

Which is the homogametic sex in the ZW system?

Males; ZZ

Which is the heterogametic sex in the ZW system?

Females; ZW

For X-linked genes, females can be…

Homozygous or heterozygous.

For X-linked genes, males can be…

Only hemizygous.

Which organisms use the ZW system?

Birds, butterflies, some reptiles, and some amphibians.

Eukaryotic chromosomes have…

Telomeres and one centromere.

Telomeres and centromeres are classified as…

Heterochromatin (transcriptionally silenced).

Heterochromatin is made of…

Clusters of satellite DNA: 100,000s to millions of tandem repeats <10 bp length.

t-loop:

End of telomere formed by G-rich 3’ overhang folding over and H-bonding with the complementary strand.

Telomeres consist of…

Tandem repeats of A and T followed by several G’s, with a LOT of repeats per telomere.

Why do telomeres have repeats?

To maintain the integrity of the chromosomal ends and protect them from fusing.

Metacentric:

Centromere is in the exact middle of a chromosome.

Submetacentric:

Centromere is off-center.

Acrocentric:

Centromere is almost to telomere, but small arms still visible.

Telocentric:

Centromere is close enough to telomere that the small arms aren’t visible.

Mitosis:

Portion of eukaryotic life cycle where chromatin condenses into thread-like chromosomes (becoming visible), aligns, and separates into nascent cells.

Interphase:

Portion of eukaryotic life cycle between mitosis…es? Chromatin is diffuse.

What are the phases of mitosis?

Prophase → Prometaphase → Metaphase → Anaphase → Telophase

What are the phases of interphase?

G1 (Growth 1) + S (Synthesis) + G2 (Growth 2)

What is the S phase?

Chromosome duplication — Occurs during interphase

Prophase:

Chromatin condenses into chromosomes; nucleus disappears

Prometaphase:

Nuclear membrane dissolves; spindle appears

Metaphase:

Chromosomes line up along metaphase plate

Anaphase:

Chromosomes break at centromeres; sister chromatids move to opposite ends of cell.

Telophase:

Nuclear membrane reforms; chromosomes unwind; cell begins become daughter cells

Cytokinesis:

Cytoplasm divides; cell wall forms in plant cells

Mitosis is ______ division.

equational

Meiosis is ______ division.

reductional

Meiosis I:

Separation of homologous chromosomes (sister chromatids remain intact); reductional division

Meiosis II:

Separation of sister chromatids; equational division

Crossing-over takes place between ______ chromatids of ______ chromosomes.

non-sister; homologous

Germ cells:

Precursors to gametes; form from specialized diploid cells; located only in gonads.

Somatic cells:

All cells that aren’t germ cells; cannot go through meiosis.

Spermatogenesis:

Process of sperm formation; occurs continuously throughout adult life.

Spermatogonium:

Male germ cell; 2n

Primary spermatocyte:

Spermatogonium that has gone through prophase I; 2n

Secondary spermatocytes:

Two cells produced by a primary spermatocyte completing meiosis I; 1n

Spermatids:

Two cells produced by a secondary spermatocyte undergoing meiosis II; 1n

Sperm:

Mature spermatid

Oogenesis:

Process of egg cell formation; mitosis occurs ONLY during embryonic development; meiosis begins in gestation and arrests in prophase I until menarche

Oogonium:

Female germ cell; 2n

Primary oocyte:

Oogonium that has entered prophase I; 2n

Secondary oocyte:

Produced by primary oocyte completing meiosis I; 1n

Polar body:

Produced by oocytes during each meiosis; disintegrates after formation

Ovum:

Produced by secondary oocyte completing meiosis II following sperm penetration; 1n

Zygote:

Produced by sperm and ovum nuclei fusing at fertilization; 2n

Nondisjunction:

Abnormal chromosome segregation resulting in abnormal chromosome numbers after cell division; can occur in mitosis or either meiosis; can result in inviable cells/gametes/embryos; can result in abnormal chromosome numbers in viable individuals.

Ploidy:

Number of chromosome sets

Haploid (1n):

One set of chromosomes

Diploid (2n):

Two sets of chromosomes

Polyploid (3n, 4n, etc.)

More than two sets of chromosomes.

Euploid:

Individual with “expected“ number of chromosomes (ex. normal diploid = 2n).

Aneuploid:

Differs from expected by one or a few chromosomes.

Nullisomy:

2n - 2

Monosomy:

2n - 1

Trisomy:

2n + 1

Polyploid:

Number of chromosomes different by entire set(s) (ex. triploid (3n), tetraploid (4n), etc.).

What causes aneuploidy?

Nondisjunction

Nondisjunction in mitosis in soma causes…

Mosaic organisms