DNA Transcription and Cell Membrane (Terms)

Genetic information in DNA

A living archive of instructions that cells use to make proteins

proteins

Build cell structures

DNA replication

The process of copying DNA before a cell divides

Accuracy of DNA replication

Important for the health and traits of new cells

Double helix

The twisted ladder shape of DNA

Nucleotide

The building block of DNA (A, T, C, G)

Complementary base pairing

A pairs with T, and C pairs with G

Semi-conservative replication

Each new DNA has one old and one new strand

Gene expression

When a cell activates specific genes depending on its function

Same

— DNA in all cells

Nerve cells

express genes for neurotransmitters

Muscle cells

express genes for protein filaments used in contraction

Transcription

The first step in gene expression where RNA is made from DNA

RNA polymerase

The enzyme that builds RNA during transcription

RNA

single-stranded

RNA sugar

Ribose

DNA sugar

Deoxyribose

Uracil

The base in RNA that replaces thymine

RNA folding

RNA folds into complex shapes using internal base pairing

mRNA

carries the genetic code from DNA to ribosomes

rRNA

forms the core of ribosomes where proteins are made

tRNA

brings amino acids to ribosomes during protein synthesis

Eukaryotic RNA polymerases

Multiple specialized polymerases for each RNA type

Prokaryotic RNA polymerase

Only one polymerase makes all RNA types

Other RNA types

Help regulate gene expression and defend against viruses

mRNA

the most variable RNA class in number and lifespan

Abundant mRNAs

Usually code for structural proteins

Rare mRNAs

Often code for signaling proteins

Structural mRNAs

can last over 10 hours

signaling mRNAs

may last less than 10 minutes

Transcriptome

All the mRNA molecules in a cell at a specific time

Transcriptome

Shows which genes are being expressed

Genome vs transcriptome

Genome is all genes; transcriptome is active genes

Example of transcriptome

Insulin mRNA in pancreas cells but not in bone cells

Ribosome

The cell structure where proteins are made

Ribosome

Made of rRNA and proteins

Polyribosome

A cluster of ribosomes making protein at the same time

Ribosome (eukaryotes)

Free in cytoplasm or attached to membranes

Membrane-bound ribosomes

Make proteins for secretion or membranes

rRNA

About half of the ribosome's mass

Protein mass in ribosome (prokaryotes)

~60 proteins

Protein mass in ribosome (eukaryotes)

Over 80 proteins

Plasma membrane

A flexible, elastic, protective barrier that separates the cell's internal components from the external environment

Subcellular membranes

Internal membranes like ER

Membrane thickness

6–8 nanometers

Fluid mosaic model

The membrane model where proteins float in a phospholipid bilayer

Phospholipid bilayer

The double layer of phospholipids that makes up the membrane

Globular proteins

Proteins that float within the phospholipid bilayer

Carbohydrate side chains

Sugars attached to membrane proteins/lipids for cell interaction

Cholesterol in the membrane

Helps stabilize membrane fluidity

Antigenicity

Membrane proteins help the immune system recognize self vs foreign cells

Selective permeability

The membrane controls what enters and leaves the cell

Passive transport

Movement of substances without energy (from high to low concentration)

Active transport

Movement of substances using energy (from low to high concentration)