Mitosis vs meiosis, cellular respiration and genetics study sheet

What every cell has

Plasma membrane

The outer covering that separates the inside of the cell from its surroundings.

Cytoplasm

The jelly-like cytosol that fills the cell, with the other cell parts suspended in it.

DNA

The cell’s genetic material.

Ribosomes

The structures that build proteins.

Prokaryotic vs eukaryotic cells

Animal vs plant cells

For the nucleus, endoplasmic reticulum, Golgi apparatus, ribosomes and the rest, see the organelles table on the cells and tissues study guide.

Cell membrane structure

Phospholipids

The main fabric. Each has a water-loving (hydrophilic) head and two water-hating (hydrophobic) fatty-acid tails. In water they line up tail to tail with the heads facing out, which makes a double layer, the lipid bilayer.

Cholesterol

Another lipid, made of four fused carbon rings, set alongside the phospholipids in the core of the membrane.

Integral proteins

Built right into the membrane; their water-hating regions sit among the phospholipid tails. Some stretch all the way across it.

Peripheral proteins

Attached to the inner or outer surface of the membrane, to integral proteins or to phospholipids.

Carbohydrate chains

Found only on the outside surface, attached to proteins (glycoproteins) or to lipids (glycolipids). Together they form the glycocalyx, which helps cells recognize each other, including “self” versus “non-self”.

The fluid mosaic model describes the membrane as a mosaic of phospholipids, cholesterol, proteins and carbohydrates that gives it a fluid character. A plasma membrane is about 5 to 10 nm thick. In a typical human cell, protein is about 50 percent of the membrane by mass, lipids about 40 percent and carbohydrates about 10 percent, though the mix varies from one membrane to another.

Mitochondria: function and structure

Mitochondria are often called the cell’s powerhouses because they make ATP, the cell’s main short-term energy carrier, by cellular respiration. In mitochondria that process uses oxygen and gives off carbon dioxide. Muscle cells, which need a lot of energy, have a very high concentration of them.

Two membranes

An outer and an inner membrane, each a phospholipid bilayer with proteins in it. The space between them is the intermembrane space.

Cristae

Folds of the inner membrane, which increase its surface area. ATP is made on the inner membrane.

Matrix

The space inside the inner membrane.

Own DNA and ribosomes

Mitochondria carry their own DNA and ribosomes, which is part of the evidence that they began as bacteria living inside larger cells (endosymbiosis).

Vocabulary first

Diploid (2n)

Two matching sets of chromosomes, one from each parent. A human body (somatic) cell is diploid, with 46 chromosomes in 23 homologous pairs.

Haploid (n)

One set of chromosomes. Human gametes, the sperm and the egg, are haploid, with 23 chromosomes each.

Homologous chromosomes

A matched pair, one from each parent, the same length and carrying the same genes in the same places, though not always the same versions of them.

Sister chromatids

The two identical copies of a chromosome made when DNA is replicated, joined at the centromere. Once they separate, each is called a chromosome.

Mitosis vs meiosis: the comparison

The cell cycle phases

1. 1

   G₁ (first gap)

   The cell grows and is very active biochemically, gathering the building blocks for DNA and proteins and enough energy to copy every chromosome.

2. 2

   S (synthesis)

   The DNA is replicated, so each chromosome becomes two sister chromatids joined at the centromere. The centrosome is duplicated too.

3. 3

   G₂ (second gap)

   The cell restocks its energy, makes the proteins needed to move chromosomes and duplicates some organelles.

4. 4

   Mitotic phase

   Mitosis (nuclear division, also called karyokinesis) followed by cytokinesis (division of the cytoplasm). G₁, S and G₂ together are called interphase.

Mitosis, phase by phase

1. 1

   Prophase

   The chromosomes condense and become visible, the nucleolus disappears and the nuclear envelope starts to break down. The centrosomes move toward opposite poles and the spindle begins to form.

2. 2

   Prometaphase

   The nuclear envelope breaks up further. Each sister chromatid develops a kinetochore at its centromere, and spindle microtubules attach to the kinetochores.

3. 3

   Metaphase

   All the chromosomes line up in one plane midway between the poles, the metaphase plate (equatorial plane). They are at their most condensed.

4. 4

   Anaphase

   The cohesin proteins holding the sister chromatids together break down, and the chromatids separate. Each, now a chromosome, is pulled toward its pole.

5. 5

   Telophase

   The chromosomes reach the poles and unwind, the spindle falls apart and a nuclear envelope forms around each set.

6. 6

   Cytokinesis

   The cytoplasm divides, giving two genetically identical daughter cells.

Cytokinesis in animal and plant cells

Meiosis I, phase by phase

Meiosis starts like mitosis, with interphase and one round of DNA replication, then runs two divisions in a row. The phases carry the same names with I or II added.

1. 1

   Prophase I

   Homologous chromosomes pair up along their whole length (synapsis), held together by a protein lattice, the synaptonemal complex. Nonsister chromatids swap segments in crossing over, seen afterward as chiasmata. Each pair, now four chromatids, is a tetrad.

2. 2

   Metaphase I

   The homologous pairs line up at the metaphase plate. Each pair faces the poles in a random direction, independent of the other pairs (independent assortment).

3. 3

   Anaphase I

   The homologous chromosomes are pulled apart toward opposite poles. The sister chromatids stay joined at their centromeres.

4. 4

   Telophase I and cytokinesis

   Two haploid cells result. Each chromosome still has two sister chromatids. There is no new DNA replication before meiosis II.

Meiosis II

1. 1

   Prophase II to metaphase II

   A new spindle forms in each of the two cells and the chromosomes line up at the middle, with one set of chromosomes in each cell.

2. 2

   Anaphase II

   The sister chromatids finally separate and move to opposite poles, much as in mitosis.

3. 3

   Telophase II and cytokinesis

   Nuclear envelopes re-form and the cells divide, leaving four haploid cells that are genetically different from one another.

Meiosis makes genetically different cells in two ways: crossing over in prophase I builds chromosomes with new mixes of maternal and paternal genes, and the random orientation of the pairs in metaphase I shuffles which chromosomes go to which cell. With 23 pairs, the random alignment alone allows over eight million (2²³) different combinations of chromosomes.

The four stages

1. 1 · Glycolysis

   Where

   Cytoplasm

   Goes in

   One glucose (6 carbons)

   Comes out

   Two pyruvate (3 carbons each), a net gain of 2 ATP and 2 NADH

   Uses 2 ATP in the first half and makes 4 in the second, so the net is 2. It does not use oxygen directly, and nearly all living organisms carry it out.

2. 2 · Pyruvate to acetyl CoA

   Where

   Mitochondrial matrix (in eukaryotes)

   Goes in

   Pyruvate

   Comes out

   Acetyl CoA, carbon dioxide and NADH

   Each pyruvate loses one carbon as CO₂, so two of the glucose’s six carbons are gone by the end of this step.

3. 3 · Citric acid cycle (Krebs cycle)

   Where

   Mitochondrial matrix

   Goes in

   Acetyl CoA joins a 4-carbon oxaloacetate to make 6-carbon citrate

   Comes out

   For each acetyl group: 2 CO₂, 3 NADH, 1 FADH₂ and 1 ATP (or GTP)

   A closed loop: the last step rebuilds the molecule the first step used. It makes very little ATP directly and does not use oxygen directly, but it depends on oxygen because the carriers it fills must hand their electrons on.

4. 4 · Electron transport chain and chemiosmosis

   Where

   Inner mitochondrial membrane

   Goes in

   NADH and FADH₂ (their electrons), oxygen

   Comes out

   Water, and most of the ATP

   The only part of glucose breakdown that uses oxygen. Electrons pass along protein complexes to oxygen, which forms water with protons. The energy pumps H⁺ across the membrane, and H⁺ flowing back through ATP synthase powers the making of ATP from ADP.

The citric acid cycle, the TCA cycle and the Krebs cycle are three names for the same pathway. “Citric acid” is its first product (citrate), “TCA” is for tricarboxylic acids such as citrate, and “Krebs” is for Hans Krebs, who worked out its steps in the 1930s.

Energy vocabulary

ATP

Adenosine triphosphate, the “energy currency” of the cell. Breaking off its end phosphate group, leaving ADP, releases energy the cell can use; adding the phosphate back takes energy.

NAD⁺ and NADH

An electron carrier. NAD⁺ is the oxidized form; NADH is the reduced form, after it has accepted two electrons and a proton.

FAD and FADH₂

A second electron carrier. FADH₂ is its reduced form.

Oxidized and reduced

A molecule that loses electrons is oxidized; one that gains electrons is reduced. The two usually happen together.

The number of ATP made per glucose varies, the textbook notes, with the species, with how electrons are shuttled into the mitochondria and with intermediates used for other jobs. Use the number your own course gives. Overall, these pathways capture about 34 percent of the energy in glucose; the rest is released as heat.

Gene

The functional unit of a chromosome: it codes for a protein and so determines a characteristic such as hair color.

Trait

A variation of a characteristic. Hair color is the characteristic; blonde, brown and black are traits.

Locus

The location of a gene on a chromosome. Homologous chromosomes carry genes at the same loci.

Allele

One version of a gene. Alleles of a gene sit at the same place on homologous chromosomes.

Dominant allele

The allele whose trait shows when an organism carries two different alleles.

Recessive allele

The allele whose trait is hidden when a dominant allele is present. It shows only when both alleles are recessive.

Genotype vs phenotype

Homozygous vs heterozygous

In the textbook’s convention a gene is named for its dominant trait, with a capital letter for the dominant allele and a lowercase letter for the recessive one. Violet flower color is dominant in peas, so VV and Vv have violet flowers and vv has white flowers.

A Punnett square

A Punnett square lists one parent’s possible alleles along the top and the other’s down the side; each box is a possible genotype of an offspring. Here is the monohybrid cross from the textbook: two heterozygous yellow-seeded pea plants (Yy × Yy), where yellow (Y) is dominant over green (y).

The four boxes give a genotype ratio of 1 YY : 2 Yy : 1 yy. Because YY and Yy both have yellow seeds, the phenotype ratio is 3 yellow to 1 green. These are expected proportions: each combination is equally likely, so real counts come out close to them with large samples.

The five antibody classes

IgG

About 80 percent of the antibodies in the blood serum.

IgM

About 10 percent of serum antibodies, and usually the first class secreted in a new immune response. Plasma cells assemble IgM into five-unit clusters (pentamers).

IgA

Found in saliva, tears, breast milk and the mucus secretions of the digestive, respiratory and genitourinary tracts.

IgE

Present in the serum in small amounts; best known as a mediator of allergy.

IgD

Present in small amounts; on the surface of naïve B cells it helps with antigen recognition and the maturing of B cells into plasma cells.

Antibodies coat and neutralize pathogens by blocking the sites that let them dock on cells, mark pathogens so that phagocytes such as macrophages and neutrophils engulf them (opsonization), and provide docking sites for complement proteins (complement fixation).

6 · Flashcards

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Cell parts, mitosis and meiosis, cellular respiration, genetics terms and antigens and antibodies. Tap a card (or press Enter) to flip it, use the arrows or the left and right keys to move, and shuffle when the order starts to feel familiar.

7 · Practice questions

20 practice questions

Mitosis and meiosis, cellular respiration, genetics terms, the cell membrane and antigens and antibodies, multiple choice, one at a time. Every answer is explained, and your score is free: no sign-up needed.