4 - Cell Structure and Composition

Vocabulary flashcards covering nucleic acids, DNA/RNA, central dogma, organelles, membranes, cytoskeleton, and related cell biology concepts.

Nucleotides

Building blocks of nucleic acids; each nucleotide has a sugar, a phosphate group, and a nitrogenous base.

Nucleic acids

Polymers of nucleotides; include DNA and RNA.

Nitrogenous base

A base that is part of a nucleotide; examples include A, G, C, T (DNA) and A, G, C, U (RNA).

Adenine (A)

Purine base that pair with thymine in DNA or uracil in RNA.

Guanine (G)

Purine base that pairs with cytosine in both DNA and RNA.

Cytosine (C)

Pyrimidine base that pairs with guanine in DNA and RNA.

Thymine (T)

Pyrimidine base in DNA that pairs with adenine.

Uracil (U)

Pyrimidine base in RNA that pairs with adenine.

Purines

Double-ring bases (A and G) found in both DNA and RNA.

Pyrimidines

Single-ring bases (C and T in DNA; C and U in RNA).

Deoxyribose

Five-carbon sugar in DNA; lacks the 2' hydroxyl group.

Ribose

Five-carbon sugar in RNA; contains a 2' hydroxyl group.

Phosphate group

Phosphate linkage that forms the sugar–phosphate backbone of nucleic acids.

Sugar-phosphate backbone

The chain of sugars and phosphates that forms the repeating backbone of DNA and RNA.

Phosphodiester bond

Covalent bond linking the phosphate of one nucleotide to the sugar of the next.

Polynucleotide

Long chain of nucleotides; a nucleic acid like DNA or RNA.

Monomer

Nucleotide; the building block of nucleic acids.

5' end

End of a polynucleotide bearing a phosphate group.

3' end

End of a polynucleotide bearing a hydroxyl group on the sugar.

Nucleoside

Nitrogenous base attached to a five-carbon sugar; lacks phosphate.

DNA

Deoxyribonucleic acid; sugar is deoxyribose; bases A, G, C, T.

RNA

Ribonucleic acid; sugar is ribose; bases A, G, C, U.

Central Dogma

DNA → RNA → Protein; with some exceptions like reverse transcription.

Transcription

Process of copying DNA into RNA within the nucleus.

Translation

Ribosome-mediated synthesis of protein using mRNA and tRNA.

mRNA

Messenger RNA; carries genetic information from DNA to ribosomes.

tRNA

Transfer RNA; brings specific amino acids to the ribosome during translation.

Ribosome

Ribonucleoprotein complex that builds proteins by translating mRNA.

Nucleus

Organelle that houses DNA; contains nucleolus and chromatin; surrounded by a nuclear envelope with pores.

Nucleolus

Nucleolus: region where ribosomal subunits are assembled and rRNA is synthesized.

Chromatin

DNA wrapped around histone proteins; condenses into chromosomes during cell division.

Histone

Protein around which DNA is wrapped to form nucleosomes.

Nucleosome

DNA wrapped around a histone core; basic unit of chromatin.

Euchromatin

Loosely packed chromatin with active genes.

Heterochromatin

Tightly packed chromatin with relatively inactive genes.

Chromosome

Visible, condensed DNA-protein complex during cell division.

Diploid

Two complete sets of chromosomes (e.g., most somatic human cells).

Haploid

One complete set of chromosomes (e.g., gametes like sperm or eggs).

Endomembrane system

Network of organelles (nuclear envelope, ER, Golgi, lysosomes, vesicles) that produces, modifies, and transports proteins and lipids.

Rough Endoplasmic Reticulum

ER with ribosomes; synthesizes and modifies proteins destined for secretion or membranes.

Smooth Endoplasmic Reticulum

ER without ribosomes; synthesizes lipids, detoxifies compounds, and stores calcium.

Golgi apparatus

Modifies, sorts, and packages proteins and lipids into vesicles for delivery.

Lysosome

Digestive organelle containing hydrolytic enzymes; degrades macromolecules.

Vesicle

Small membrane-bound sac used for transport within the cell.

Endosome

Vesicle involved in sorting internalized material during endocytosis.

Exosome

Vesicle involved in secretion and intercellular communication.

Mitochondrion

Powerhouse of the cell; site of ATP production; contains own DNA and ribosomes; can initiate apoptosis.

Chloroplast

Site of photosynthesis in plants; contains thylakoids, grana, and stroma; has own DNA and ribosomes.

Peroxisome

Organelle involved in detoxification and reactive oxygen species metabolism.

Cytoskeleton

Network of filaments that provides structure, facilitates movement, and organizes organelles.

Microtubules

Hollow tubes of tubulin; maintain cell shape and guide chromosome movement.

Microfilaments

Actin filaments; support cell shape and enable movement.

Intermediate filaments

Rope-like proteins providing mechanical strength and organelle anchoring.

Centrosome (centrioles in animals)

Microtubule-organizing center important for spindle formation during cell division.

Plasma membrane

Phospholipid bilayer with cholesterol and proteins that defines cell boundary and regulates traffic.

Cell wall

Rigid layer outside the plasma membrane in plants (and some fungi/bacteria); mainly cellulose in plants.

Plasmodesmata

Cytoplasmic channels through plant cell walls enabling intercellular communication.

Glycoprotein

Protein with carbohydrate chains; involved in cell recognition and signaling.

Glycolipid

Lipid with carbohydrate chains; important for cell recognition.

Cholesterol (membrane)

Sterol that modulates membrane fluidity and stability.

Integral membrane proteins

Proteins embedded in the hydrophobic core of the membrane; often channels or receptors.

Peripheral membrane proteins

Proteins attached to the membrane surface; support or signaling roles.

Glycosylation

Addition of carbohydrate groups to proteins, occurring mainly in ER and Golgi.

Signal peptide

Short amino acid sequence that targets a protein to the ER.

Signal Recognition Particle (SRP)

Ribonucleoprotein that recognizes the signal peptide and guides ribosomes to the ER.

Endosymbiotic theory

Mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by a host cell.