Chap 4 PT 5 Flashcards
The nucleus
Largest structure in cell
Cell’s control center
Typically only one per cell
Exceptions
Erythrocytes with no nuclei
Skeletal muscle cells with many nuclei
Nuclear envelope
Double phospholipid membrane enclosing nucleus
Separates cytoplasm from fluid within nucleus, nucleoplasm
continuous with rough ER
Nuclear pores
Open passageways allow passage of large molecules into and out of nucleus (not DNA)
Ions and water soluble molecules pass through
Nucleolus
Dark-staining, spherical body
Not membrane-bound
Composed of protein and RNA
Produces small and large ribosome subunits
Not present in all cells
E.g., more than one in nerve cells due to production of many proteins
E.g., absent in sperm cells because no proteins are produced
histones
Each double helix is wound around
Together form nucleosomes
Chromatin
When not dividing, DNA are in form of finely filamented mass called
Chromosomes
When dividing, DNA chromatin becomes tightly coiled
DNA
master blueprint for all proteins in your cells (or a whole recipe book)
Gene
DNA segment that carries the information for building one protein or polypeptide chain
(a single recipe)
“encoded
the sequence of nitrogenous bases along each side of the ladder-like DNA molecules (how the recipe is written)
Transcription
complementary mRNA is made from a DNA gene
Occurs in Nucleus
Translation
The information carried in mRNA molecules is “decoded” and used to build proteins
Occurs in Cytoplasm
Ribosomes & tRNA are needed
Translation
Code in nucleotide sequence of mRNA translated into the “language” of proteins.
Messenger RNA
From the nucleus attaches to a ribosome (with large and small subunits). Ribosomes are sites of protein synthesis
Transfer RNA
its job is to carry or “transfer” appropriate amino acids to the ribosome
A DNA triplet corresponds to an mRNA codon
Each codon on mRNA is associated with a particular amino acid
