Cell Biology

cell

smallest unit that can perform all functions of life (body basically consists of huge collection of specialized cells)

cell theory

1. all living organisms are made of cells

2. the cell is the basic unit of life

3. all cells come from pre-existing cells

Cytoplasm

everything inside the cell except the nucleus (organelles, cytoskeleton, cytosol)

Cytosol

fluid portion inside the cell (mostly water, ions, dissolved molecules)

Cytoskeleton

internal support system of the cell (cell shape, movement, transport inside cell, cell division)

1. Microfilaments

2. Intermediate filaments

3. Microtubules

Microfilaments (actin)

cause movement and muscle concentration

Intermediate filaments

for strength/stability

Microtubules

transport, spindle fibers in mitosis, form cilia/flagella

Cell membrane

separates inside of cell from outside environment, contains phospholipid bilayer, proteins, cholesterol, glycoproteins

selectively permeable

some substances pass easier than others

Passive Membrane Transport

no energy needed, high concentration → low concentration

Diffusion

small molecules move directly through membrane

Osmosis

movement of water through semipermeable membrane, moves toward higher solute concentration

Facilitated Diffusion

uses transport proteins, still no ATP required

Active Transport

requires ATP to move substances against concentration gradient (low→high)

Endocytosis

Cell takes material in

Exocytosis

Cell releases material out

Nucleus

stores DNA

contains: chromosomes, chromatin, nucleolus

Chromatin

DNA + proteins

Nucleolus

produces ribosomes

Mitochondria

“powerhouse of the cell” ATP production, site of cellular respiration

Cristae

folds of inner membrane, increases surface area for ATP production

Ribosomes

for protein synthesis, can be free in cytoplasm or attached to rough ER

Rough ER

contains ribosomes for protein synthesis

Smooth ER

for lipid synthesis, detoxification

Golgi Apparatus

modifies, packages and transports proteins

Lysosomes

contain digestive enzymes → breakdown of waste, recycling

Peroxisomes

contain oxidative enzymes → detoxification, fatty acid breakdown

Cell Cycle

series of stages a cell goes through to grow, copy its DNA and divide into two new cells → tightly controlled by checkpoints and proteins so cells only divide when necessary

Interphase

first three phases together → grows, copies DNA, prepares to divide (G1, S, G2)

G1 Phase

Growth 1 → cell grows larger, produces proteins, duplicates organelles but DNA is not copied yet

S Phase

S=Synthesis → DNA replication

each chromosome becomes two sister chromatids connected at centromere

Sister Chromatids

identical copies of a chromosome

G2 Phase

= Growth 2 → continues growing, prepares for mitosis, checks replicated DNA

M Phase

=Mitosis → nuclear divison

Cytokinesis

after mitosis, splits the whole cell

Result of Cell Cycle

one parent cell → two genetically identical daughter cells

Mitosis

main purpose is to produce identical body cells used for growth, tissue repair

before mitosis DNA exists as chromatin (uncondensed DNA)

during mitosis chromatin condenses into visible chromosomes

Prophase

chromosomes condense, sister chromatids become visible, spindle fibers begin forming, centrosomes move to poles

Mitotic Spindle

made of microtubules, move chromosomes

Prometaphase

nuclear envelope breaks down, spindle fibers attach to kinetochores

Kinetochore

protein structure on centromere, microtubules attach here

Metaphase

Chromosomes align in middle of cell → metaphase plate

Anaphase

sister chromatids separate, cohesion proteins break down, microtubules pull chromatids toward opposite poles

Telophase

chromosomes decondense, nuclear envelopes reform, spindle disappears → two nuclei exist

Cytokinesis

final step, cell divides completely: cytoplasm splits, two daughter cells formed

PMAT

Prophase, Metaphase, Anaphase, Telophase

G0 Phase

resting phase some cells enter after division

Cell Cycle and Cancer

cancer occurs when cell cycle regulation fails → cells divide uncontrollably usually due to mutations in checkpoint genes

Cell Cycle ensures

• DNA is copied correctly

• chromosomes are distributed equally

• new healthy cell are produced

Karyotype

an organized picture of all chromosomes in a cell

humans have 46 chromosomes organized into 23 pairs (22 pairs autosomes, 1 pair sex chromosomes)

Sex Chromosomes

Female: XX

Male: XY

Karyotypes are used to

detect chromosomal abnormalities, extra/missing chromosomes

Mitosis produces

2 identical diploid cells

Meiosis produces

4 genetically different haploid cells

Diploid (2n)

2 chromosome sets

Haploid (n)

1 chromosome set

without meiosis

chromosome number would double every generation

semi-conservative replication of DNA

each new DNA molecule contains one old strand and one new strand

Helicase

unzips DNA (breaks hydrogen bonds)

DNA Polymerase

adds complementary nucleotides (uses base-pairing rules)

Gene Expression

using genetic information to make proteins

Transcription

making RNA from DNA

1. DNA unwinds

2. RNA polymerase builds mRNA

3. complementary pairing occurs (uracil instead of thymine)

Product: mRNA→ carries genetic information to ribosome

Translation

making protein from mRNA

—> ribosome reads codons

Codon

3 RNA bases coding for one amino acid

tRNA

brings amino acids, has anticodon matching mRNA codon → form polypeptide/protein

Gene

DNA segment coding for a protein

Alleles

different versions of a gene

Genotype

genetic makeup

Phenotype

visible trait

Dominant Allele

expressed if present

Recessive Allele

only expressed if two copies exist

Homozygous

two identical alleles

Heterozygous

two different alleles

Mendels Laws

1. Law of Segregation 2. Law of Independent Assortment 3. Punnett Squares

Law of Segregation

each organism has two alleles for each gene, during meiosis alleles separate, gametes receive one allele only

Law of Independent Assortment

different genes assort independently during gamete formation → increases genetic variation

Punnet Squares

used to predict inheritance probabilities

Mutation

change in DNA sequence, can be harmful/neutral/beneficial

Point mutation

single base change

Chromosomal mutation

large chromosome changes

cell cycle cancer

happens when cell cycle loses control → cells divide uncontrollably, ignore checkpoints and continue growing even when they should stop, usually because of mutations in genes that regulate the cell cycle

Proto-oncogenes

stimulate cell division, become oncogenes if mutated → cell division becomes excessive

tumor suppressor genes

stop division/repair DNA → if damaged checkpoints fail and abnormal cells continue dividing

Tumor

mass of rapidly dividing cells

benign tumor

stays localized, less dangerous

malignant tumor

invasive, can spread

metastasis

spread of cancer cells to other parts of the body

cancer

a disease caused by uncontrolled cell division due to mutations affecting cell cycle regulation