wk1: nucleus

Cellular Organisation: the nucleus

We have ~ 30 trillion cells in the body: ~200 different types of cells

  • white and red blood cells - specialised to protect the body against threats - carry oxygen & carbon dioxide around the bloodstream to all cells and tissue

  • epithelial cells - cells line the surfaces of organs and structures, playing a crucial role in protection, secretion, and absorption.

  • sperm cells - specialised for reproduction - carry genetic material

  • neurons within brain and CNS that communicate/ send messages around the body

  • fat cells - provide energy storage, insulation, and play a role in hormonal regulation

  • bone cells - provide structural support for the body, enable movement, and assist in the production of blood cells.

  • muscle cells - contract to enable movement & maintain posture

  • Each cell type is unique as they require different structural features to perform their specific functions

  • All cells descend from a single cell (fertilised ovum/ zygote)

  • A zygote is very large, totipotent (ability to form any type of cell)

  • Proliferation means cell division

Differentiation means cell maturation/ specialisation

Flow chart of cell proliferation

Nucleus

  • some cells have multiple nuclei - big cells need lots of energy, require more than 1 control centre

  • some cells don’t have a nucleus, such as red blood cells as this makes it easier for them to squeeze through tight capillaries

  • Functions of Nucleus
    1) Houses and protects our DNA
    2) regulates DNA activity (including expression and activation/ suppression
    3) Within the nucleus is a nucleolus (NU CLE OH LUS) that produces ribosomal subunits (building blocks for ribosomes) that are transported into cytoplasm and used to form ribosomes for protein synthesis

Nuclear Envelope & Nuclear Pores

  • The nuclear envelope: double membrane that encloses the nucleus - protective barrier

  • Nuclear pores: passages that allow communication between the nucleus and cytoplasm

Nucleolus

  • Nucleolus: responsible for ribosome synthesis and assembly (ribosomes = protein synthesis)

  • Amembranous (held together by surface tension)

  • Contains DNA, RNA and proteins

  • easier to see in cells that are actively synthesising proteins

DNA

  • DNA contains genetic instructions

  • we have ~2 metres of DNA in each cell

  • DNA wraps itself around proteins (histones) and folds (chromatin), then assembles into 23 pairs of chromosomes in each cell

  • chromosome consists of a long DNA molecule encased in proteins

Chromatin = 30% DNA + 60% histones + 10% RNA

  • Chromatin - exists in two forms
    1) Heterochromatin - inactive cell - highly condensed, intensely stained
    2) Euchromatin - active cell - dispersed, lightly stained

DNA to Protein

  • Messenger RNA (mRNA) single-stranded copy of a gene, containing instructions to make a protein: mRNA is the end product following transcription

  • Transfer RNA (tRNA) interpret the instructions from mRNA > bring in specific amino acid (building block) to make the protein

  • Ribosomal RNA (rRNA) are the structural unit for ribosomes (protein-making factories)

  • Translation takes place in the cytoplasm when the mRNA docks to the ribosome, where the mRNA sequence is read and the specific protein is created

Transcription

  • Transcription is when mRN makes a copy of the DNA instructions for a protein to be created - the mRNA is sent from the nucleus into the cytoplasm to be translated into a protein

  • During the process of transcription the DNA uncoils - gene sequence is exposed > enzymes bind to the exposed DNA and create a copy (single-stranded mRNA)

Translation: sequence of events

  • Initiation: mRNA binds to ribosome > ‘start codon’ is recognised & tRNAs begin delivering specific amino acids

  • a codon is a sequence of three nucleotides on the mRNA that specifies a particular amino acid or serves as a stop signal during protein synthesis.

  • Elongation: amino acids link together to form a polypeptide chain (protein)

  • Termination: when the ‘stop codon’ is reached, the polypeptide chain is released from the ribosome

Redundancy reduces the chance that a DNA mutation will change the amino acid it codes. Multiple different codons (sequences of three nucleotides in mRNA) can encode the same amino acid.