A&P cellular biology (3) Flashcards
Protein synthesis
(creation of proteins)
1. Occurs in cells with nucleus & DNA (no nucleus = no DNA = no protein synthesis) – some cells w/out nucleus have no DNA and thus cannot divide. E.g. red blood cells. They live for approx. 120 days.2. Protein synthesis begins in the nucleus (DNA) & ends in the cytoplasm (RNA)3. The original DNA unravels, and only 1 strand is copied by RNA polymerase each time.
protein synthesis two steps
The making of protein through 2 key steps:
Transcription
Translation
DNA RNA protein
base triplet transcription codon + anti-codon translation amino acids
DNA: Double-stranded, nucleus
RNA: Single-stranded, nucleus and cytoplasm
Protein: Sequence of amino acids determines structure, anywhere in
cell
Transcription
– “reading & copying” the DNA into RNA
occurs in the NUCLEUS (step 1)
“Transcribing” the original information which is the DNA template.
Each three nucleotide bases (BASE TRIPLET) in DNA strand corresponds to one codon (RNA).
step 1
Steps:
A small section of DNA (containing the gene to be transcribed) uncoils within the nucleus (recall, it’s a db-helix). Only 1 strand is transcribed. Once done the DNA recoils back into its characteristic DB-helix.
mRNA
step 2
An enzyme called RNA-polymerase begins TRANSCRIPTION
at the promoter region (start of the gene) by matching the complementary nucleotide bases. For example,…..
(A) (U) – normally, this would be T, but in RNA, T is replaced with U)
(G) (C)
(T) (A)
(C) (G)
(G) (C) … and so forth … .
DNA new RNA
strand strand
Note: If you know what the DNA nucleobases are, you can always determine the complimentary RNA nucleobases.
step 3
- TRANSCRITPTION continues until the RNA
polymerase reaches the terminator region of the
gene, which signals to the enzyme that this is the
end of the DNA strand required for reading
(different proteins will be made from different
strands of DNA at different times depending of the
needs of the cell at any give time).
step 4
- RNA-polymerase detaches at the terminator
region and may go on somewhere else to start
another transcription process (on the same or
different DNA strand), thus leaving behind the pre-
mRNA.
step 5
The new pre mRNA strand must now be edited via snRNP’s (“snurps”) – small nuclear ribonuclear proteins, which remove the introns (useless segment) and merges the exons (useful segments). This is called SPLICING!!!!
In essence, snRNPS is the editor of pre-mRNA before it enters translation.
Alternative splicing – a process by which snRNPS will splice a pre-mRNA strand differently at different times to produce different mRNA strands which are then translated to different proteins (from the same pre-mRNA!)
step 6
- The newly edited RNA strand is now called mRNA (messenger-RNA), and goes onto the ribosomes in the cytoplasm for step #2, TRANSLATION
transcription IN NUCLEUS
Transcription takes place in the NUCLEUS starting with unraveling of DNA.
An enzyme, RNA POLYMERASE reads triplet bases of DNA, copying its compliment and making
pre-mRNA (IMMATURE)
pre-mRNA is edited and then sent out to the ribosomes in ER for translation into proteins.
Translation IN CYTOPLASM
1
– “translating/deciphering the mRNA into amino acid chains (making proteins)
occurs in the CYTOPLASM, on ribosomes.
Steps:
1. The edited mRNA from transcription coming from nucleus attaches to rRNA (ribosomal RNA) in the cytoplasm which has 2 subunits, a larger unit and a smaller subunit
2
- The smaller subunit holds the mRNA in place, while the larger unit has 2 sites, A site P site, for attachment of tRNA (transfer RNA) that carries with it, a specific amino acid (aa).
the section on the mRNA that is read is called the CODON, and this always occurs in triplet of nucleotide bases. Thus, the complimentary triplet segment on the tRNA is called the ANTICODON. Each anticodon on the tRNA encodes for a specific AMINO ACIDS, which is already attached. This is the point in which the mRNA strand is converted to an Amino Acids Chain.
Ex…AUG – the codon (on the mRNA), is matched via its complementary UAC – the anticodon (on tRNA) which produces the *aa: methionine, and is always the start of a new polypeptide chain of amino acid (ALL protein in the body starts with methionine) Thus, AUG is the initiator codon, UAC is the initiator anticodon, and the tRNA that is involved in this is called the
* initiator t-RNA
4
tRNA always binds to site A first, then shifts to site P (with the exception of UAC, which always binds to site P first, b/c it is the initiator tRNA). Then, when the next anticodon comes along with the next set of 3 aa’sthey’ll land onto the A site, then shift to the P site,… etc….
5
- this process continues to build the polypeptide chain*, with peptide bonds holding the new aa’s together, until it reaches a STOP CODON. (this stop codon can be any sequence of nucleotide base pairs. Again, it all depends on what protein the cell is trying to build based on its physiological need)
6
- Sometimes multiple ribosomes will attach to the same mRNA to produce multiple copies of the SAME aa chain. These are called polyribosomes. (this occurs if we need many of the same aa chains to produce many of the same proteins)
7
- Then the newly formed poly-peptide chain of amino acids falls off and is transported to the GB for further processing into functional proteins or modified with sugars & or fats.
TRANSLATION CONDENSED
Translation
mRNA from transcription from the nucleus is “translated” in to amino acids via ribosomes.
*The “small unit” holds the mRNA in place
The “larger unit” is a docking place for tRNA which carries with it a specific amino acid
The amino acids are built in sequential order until the desired amino acids are built.
The polypeptide chain breaks off and goes to the Golgi bodies for more modifications
cell division
definitely need to know cell division slide picture from class slides
duplicated is exactly the same
replicated is mostly the same
This is the process of replication and division of mature cells to form new daughter cells.
There are 2 major types of cell division in the body: MITOSIS & MEIOSIS
Every human cell has 46 chromosomes (except mature sperm and egg)
1 set of chromosomes is designated
“n” – called HAPLOID
2 sets is designated
“2n” – called DIPLOID
The 2 chromosomes that make up each pair of replicated chromosome encode for the SAME trait and look identical thus are called HOMOLOGOUS chromosomes.
1 from mom, 1 from dad. That’s why you might have mom’s eyes, and your sibling has dad’s.
The chromosomes that encode for sex differentiation, i.e. male vs female, are called the sex chromosomes. For males it’s XY and for females, it’s XX (the father carries the Y gene). These will look slightly different.
1-22 CROMOSOMES ARE AUTOSOMES
***Mature muscle cells & (NEURONS) brain/spinal cord nerve cells **CANNOT replicate and undergo cell division (this means that you are born with a set # of progenitor muscle and nerve cells that will mature & develop as you mature into the total # that you were destined to have). However, upon reaching full maturity, once damaged, they will not be replicated or divide).
somatic cells (not a sex cell)
Somatic cells (aka non gonadal, ie. non-sperm, non-egg, Non-reproductive meiosis)
The goal here is to produce 2 cells that are identical, each with the same # of chromosomes as each other as well as to the parent cell, to replace dead or injured cells. This occurs in skin cells, hair cells, most epithelial cells, connective tissue, etc….
2 major phases: Interphase & Mitosis
2 major phases
KNOW THE INTERPHASE/ MITOTIC PHASE DIAGRAM IN
A&P SLIDES
2 major phases:
a. INTERPHASE – includes:
i) new cells enter G1 phase (G-rowth phase 1), which continue to grow, organelles are replicated and cell is highly metabolically active making its own organelles and enzymes. Centrosome creation/replication is initiated here.
ii) DNA replicated in “S” (S-ynthesis) phase [fig 3.31 pg 94] – depiction of DNA replication prior to cell division – DNA is copied here. 46, 23 from mom, 23 from dad, are copied so in essence, we get 92 chromosomes)
iii) G2 phase, (G-rowth 2 phase) – cells coming from DNA synthesis continues to grow, proteins & enzymes are synthesized, centrosomes replication is complete at the end of this stage.
Everything here is in preparation for CELL DIVISION ie MITOSIS.
mitotic phase
acronym-PMAT
b. PROPHASE –
(early) chromatin become dense and form chromosomes. Sister chromatids unite to form characteristic X SHAPE with a central centromere. A kinetochore helps stabilize the chromosome centromere.
(late) nuclear envelope breaks down, centrosomes migrate to the poles & mitotic spindles form from centrioles to the centromere.
METAPHASE – (MIDDLE)
chromosomes (all 46 of them) line up in a single line along the metaphasic plate (aka metaphase plate or equatorial plane) SINGLE LINE
anaphase
ANAPHASE – (a-way)
(early) centromeres split apart* due to shortening of mitotic spindles towards the poles pulling ½ of the chromosome, ie each chromatid with it (the sister chromatids split apart).
separation of organelles is called: cytokinesis – “cell movement”
telophase
TELOPHASE – (t-wo)
(early) cleavage furrow (pinching) grows larger & chromatids are now at the poles
(late) nuclear envelope reforms in each daughter cell, & the plasma membrane is regenerated.
After mitosis, we have 2 new identical daughter cells, each w/ the same amount & type of genetic information as each other and as the original parent cell (that’s why hair, skin, epithelial cells are always look and function the same).
Cells are considered 2n = 46 chromosomes
Reproductive cells
(aka gonadal cells, germ cells, sperm egg) (HAPLOID)
- Mitosis does occur in germ cells to make 2n primary spermatocytes and oocytes.
- It is these primary cells that will enter the MEIOSIS process*
Stem sperm and egg cells (spermatogonia + oogonia) each have 46 (2n) # of chromosomes which are replicated during the “S” phase prior to entering meiosis I.
In boys, @ puberty, with an increase in testosterone, the primary spermatocytes enter meiosis I then meiosis II immediately. This results in the production of mature sperm each with 23 chromosomes.
in females
In females, the oocyte has already begun
meiosis I in fetal development before entering
*suspended development until puberty.
Then, at puberty, estrogen & progesterone kick in to
cause one egg to mature and be released
approx. every 28 days (suspended in
metaphase II), a process called ovulation.
These cells will finish Meiosis II when and
only it is fertilized!!
meiosis
genetic diversity
Meiosis is the process of replication & division of diploid cells (cells with 46 i.e. full complement of chromosomes) that results in halving of the total number of chromosomes to produce 4 haploid gamete cells (23, half # of chromosomes).
This process takes place in the testicles of males &
ovaries of females
The full # of chromosomes is restored at fertilization when/if it occurs.
23 (n) from the mother, 23 (n) from the father
Gamete is a daughter cell with 23 chromosomes.
A ZYGOTE is the union of 2 GAMETES. It is the zygote that develops into a blastocyst which then implants into the uterus!
a gamete is
a daughter cell with 23 chromosomes.
a zygote is
A zygote is the union of 2 gametes.
It is the zygote that develops into a BLASTOCYST which then implants into the uterus!
gamete
zygote
blasocyst
Gamete – mature sperm or egg
Zygote – union of a sperm and egg
Blastocyst – 8-celled zygote that implants into the uterine wall
